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  • Nitrogen fixation  (148)
  • Calcium  (143)
  • Springer  (291)
  • 1980-1984  (214)
  • 1975-1979  (77)
  • 1925-1929
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Planta 150 (1980), S. 299-302 
    ISSN: 1432-2048
    Schlagwort(e): Glyoxylate ; Isonicotinic acid hydracide ; Medicago ; Nitrogen fixation ; Photorespiration ; Rhizobium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nitrogen fixation (measured as acetylene reduction) by whole nodulated alfalfa plants was stimulated when the plants were treated with isonicotinic acid hydracide (INH) and glyoxylate, both inhibitors of the glycolate pathway of carbohydrate metabolism, at concentrations of 300 and 100 mM, respectively. Reducing energetic loses caused by photorespiration results in an increase in the symbiotic nitrogen fixation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Planta 152 (1981), S. 450-456 
    ISSN: 1432-2048
    Schlagwort(e): Calcium ; Cell elongation ; Gibberellin ; Lactuca ; pH and growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The relationship between calcium ions and gibberellic acid (GA3)-induced growth in the excised hypocotyl of lettuce (Lactuca sativa L.) was investigated. The short-term kinetics of growth responses were measured using a linear displacement transducer. Test solutions were added either as drops to the filter paper on which the hypocotyl stood (“non-flow-past”) or by switching solution flowing past the base of hypocotyl (“flow-past”), resulting in differences in growth behavior. Drops of CaCl2 added at a high concentration (10 mM) inhibited growth within a few minutes. This inhibition was reversed by ethylenediaminetetraacetic acid (EDTA). Drops of EDTA or ethyleneglycol-bis(2-aminoethylether)-tetraacetic acid caused a rapid increase in growth rate. Growth induced by EDTA was not further promoted by GA3. A continuous H2O flow resulted in growth rates comparable to those in response to GA3. Addition of CaCl2 to the flow-past medium inhibited growth and this inhibition was reversed by a decrease in CaCl2 concentration. The growth rate was found to be a function of CaCl2 concentration. When a constant CaCl2 concentration was maintained by the flow-past medium, a shift in pH from 5.5 to 4.25 had no obvious effect on hypocotyl elongation. Gibberellic acid was found to reverse the inhibitory effect of CaCl2, causing an increase in growth rate similar to that found previously when GA3 was added to hypocotyls grown in H2O under non-flow-past conditions. We propose that gibberellin controls extension growth in lettuce hypocotyl sections by regulating the uptake of Ca2+ by the hypocotyl cells.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Planta 152 (1981), S. 544-552 
    ISSN: 1432-2048
    Schlagwort(e): Ammonium assimilation ; Lichens ; Nitrogen fixation ; Peltigera
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The Nostoc in the cephalodia of the lichen Peltigera aphthosa Willd. fixed 15N2 and the bulk of the nitrogen fixed was continuously transferred from it to its eukaryotic partners (a fungus and a green alga, Coccomyxa sp.). Kinetic studies carried out over the first 30 min, after exposure of isolated cephalodia to 15N2, showed that highest initial 15N2-labelling was into NH 4 + . After 12 min little further increase in the NH 4 + label occurred while that in the amide group of glutamine and in glutamate continued to increase. The 15N-labelling of the amino group of glutamine and of aspartate increased more slowly, followed by an increase in the labelling of alanine. When total incorporation of 15N-label was calculated, the overall pattern was found to be rather similar except that, throughout the experiment, the total 15N incorporated into glutamate was about six times greater than that into the amide group of glutamine. Pulse chase experiments, in which 14N2 was added to cephalodia previously exposed to 15N2, showed that the NH 4 + pool rapidly became depleted of 15N-label, followed by decreases in the labelling of glutamate, the amide group of glutamine and aspartate. The 15N-labelling of alanine, however, continued to increase for a period. When isolated cephalodia were treated with L-methionine-SR-sulphoximine, an inhibitor of glutamine synthetase (EC 6.3.1.2), and azaserine, an inhibitor of glutamate synthase (EC 2.6.1.53), there was no detectable labelling in glutamine although the 15N-labelling of glutamate increased unimpaired. On treating the cephalodia with amino-oxyacetate, an inhibitor of aminotransferase activity, the alanine pool decreased. Evidence was obtained that glutamine synthetase and glutamate synthase were located in the Nostoc, and that glutamate dehydrogenase (EC 1.4.1.4) and various amino-transferases were located in the cephalodial fungus. Possible implications of these findings are discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 1432-2048
    Schlagwort(e): Ammonia ; Nitrogen fixation ; Nodule ; Senescence (root nodules) ; Ureide ; Vigna
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract During early development (up to 18 d after sowing) of nodules of an “effective” cowpea symbiosis (Vigna unguiculata (L.) Walp cv. Vita 3: Rhizobium strain CB756), rapidly increasing nitrogenase (EC 1.7.99.2) activity and leghaemoglobin content were accompanied by rapid increases in activities of glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), enzymes of denovo purine synthesis (forming inosine monophosphate) xanthine oxidoreductase (EC 1.2.3.2), urate oxidase (EC 1.7.3.3), phosphoenolpyruvate carboxylase (EC 4.1.1.31) and led to increased export of ureides (allantoin and allantoic acid) to the shoot of the host plant in the xylem. Culturing plants with the nodulated root systems maintained in the absence of N2 (in 80 Ar: 20 O2, v/v) had little effect on the rates of induction and increase in nitrogenase activity and leghaemoglobin content but, in the absence of N2 fixation and consequent ammonia production by bacteroids, there was no stimulation of activity of enzymes of ammonia assimilation or of the synthesis of purines or ureides. Addition of NO 3 - (0.1–0.2 mM) relieved host-plant nitrogen deficiency caused by the Ar: O2 treatment but failed to increase levels of enzymes of N metabolism in either the bacteroid or the plant-cell fractions of the nodule. Premature senescence in Ar: O2-grown nodules occurred at 18–20 d after sowing, and resulted in reduced levels of nitrogenase activity and leghaemoglobin but increased the activity of hydroxybutyrate oxidoreductase (EC 1.1.1.30).
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Planta 158 (1983), S. 320-328 
    ISSN: 1432-2048
    Schlagwort(e): Calcium ; Egeria ; Fluorescent probe ; Ions, group II ; Symplast
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The hydrophyllic dyes fluorescein glutamic acid, fluorescein glutamylglutamic acid (F(Glu)2), fluorescein hexaglycine, fluorescein leucyldiglutamyl-leucine and 6-carboxyfluorescein are unable to pass the plasmalemma in leaves of E. densa. However, when injected into single cells the dye conjugates of molecular weight 665 dalton or less move freely from cell-to-cell. This intercellular movement presumably occurs via the plant symplast. Movement of F(Glu)2 from the injected cell occurs with greatly reduced frequency when Ca2+, Mg2+ or Sr2+ are injected into the cell immediately prior to the dye. The fraction of dye injections leading to movement declines with increasing group II ion concentration in the electrode tip, up to 10 mM. Sodium and K ions do not affect dye movement. When dye injection is delayed 30 min after Ca2+ injection, dye movement is no longer inhibited. Thus the cells recover from the Ca2+ injection, indicating that the ion does not cause major cell damage. Recovery from Mg2+ injection is not complete within 60 min. Treatment of leaves with chemicals expected to raise the concentration of free intracellular group II ions, notably the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, the inhibitor of mitochondrial Ca2+ uptake trifluralin, or the ionophore A23187 also inhibits dye movement, while the calmodulin inhibitor trifluoperazine does not. Cytoplasmic streaming is inhibited by Ca2+ or Mg2+ injection and by the metabolic inhibitors. However when streaming is stopped by cytochalasin B, dye movement is not inhibited. Hence steaming is not necessary for dye movement. Thus the cytoplasmic concentration of free group II ions may directly regulate the permeability of the plant symplast.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    ISSN: 1432-2048
    Schlagwort(e): Alnus ; Ammonium ; Carbon translocation ; Endophyte damage ; Nitrogen fixation ; Root nodule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Cloned plants of Alnus incana (L.) Moench were inoculated and grown without combined nitrogen for seven weeks. The effects of ammonium on the function and structure of the root nodules were studied by adding 20 mM NH4Cl (20 mM KCl=control) for four days. Nitrogenase activity decreased to ca. 50% after one day and to less than 10% after two days in ammonium treated plants, but was unaffected in control plants. The results were similar at photon flux densities of 200 and 50 μmol m-2 s-1. At the higher light level the effect was concentration dependent between 2 and 20 mM NH4Cl. The recovery was slow, and more than 11 d were needed for plants treated with 20 mM ammonium to reach initial activity. The distribution of 14C to the root nodules after assimilation of 14CO2 by the plants was not changed by the ammonium treatment. Microscopical studies of root nodules showed high frequencies of endophyte vesicles being visually damaged in nodules from ammonium-treated plants, but not in nodules from control plants. When nitrogenase activity was restored, visually damaged vesicles were again few, whereas young developing vesicles were numerous. The slow recovery, the 14C-translocation pattern, and the structural changes of the endophyte indicate a more complex mechanism of ammonium influence than simply a short-term reduction in supply of carbon compounds to the nodules.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Planta 151 (1981), S. 265-271 
    ISSN: 1432-2048
    Schlagwort(e): Calcium ; Cation exchange ; Lycopersicon esculentum ; Rhythm ; diurnal Transport (calcium) ; Zea mays
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) and maize (Zea mays L. cv. spec.) plants were supplied with 45Ca-labeled nutrient solutions for a period of 8 or 16 h in the dark, in the light, or in a light-dark régime. Plant parts were analyzed for 45Ca content. The partitioning of 45Ca between mature leaves and meristems was shown to be affected by the presence of light. The transport of 45Ca to meristems was higher in a dark period than in a comparable light period. Experiments with excised tomato shoots yielded similar distribution patterns of 45Ca over leaves and meristems, thus excluding root pressure as the main driving force for the enhanced import of 45Ca into the meristems in the dark. Results are discussed in terms of cation-exchange transport and competition between the various calcium sinks.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    ISSN: 1432-2048
    Schlagwort(e): Bryophyta ; Bud formation (moss) ; Calcium ; Chlorotetracycline ; Cytokinin ; Funaria
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We have investigated the changes in membrane-associated calcium that occur during cytokinin induced bud formation in Funaria hygrometrica Hedw. using the fluorescent Ca2+-chelate probe chlorotetracycline (CTC). In the target caulonema cells a localization of CTC fluorescent material becomes evident at the presumptive bud site 12 h after cytokinin treatment. By the time of the initial asymmetric division this region is four times as fluorescent as the entire caulonema cell. Bright CTC fluorescence remains localized in the dividing cells of the bud. To relate the changes in CTC fluorescence to changes in Ca2+ as opposed to membrane-density changes we employed the general membrane marker N-phenyl-1-naphthylamine (NPN). NPN fluorescence increases only 1.5 times in the initial bud cell. We conclude that the relative amount of Ca2+ per quantity of membrane increases in this localized area and is maintained throughout bud formation. We suggest that these increases in membrane-associated Ca2+ indicate a localized rise in intracellular free Ca2+ concentration brought about by cytokinin action.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    ISSN: 1432-2048
    Schlagwort(e): Allantoin ; Amino acids ; Bleeding sap ; Nitrogen fixation ; Phaseolus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Dwarf french beans, Phaseolus vulgaris L., were grown with or without inoculation with rhizobia (strain 3644), and with or without a combined nitrogen source (nitrate or ammonium ions). The distribution of radioactivity into products of dark 14CO2 assimilation was studied in roots or nodules from these plants. A detailed study was also made of the distribution and rates of excretion of nitrogen in xylem bleeding sap in 28 day old plants grown on the various sources of nitrogen. Whereas detached nodules accumulated radioactive glycine, serine and glutamate when incubated with 14CO2, bleeding sap from plants root fed 14CO2 contained low levels of radioactivity in these compounds but higher levels in allantoin. Chemical analysis showed allantoin to be the major compound transported in the xylem of nodulated plants, whether or not they were fed on combined nitrogen. In contrast uninoculated plants accumulated mainly amino acids in the bleeding sap, the amount and chemical composition of which depended on the combined nitrogen source.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Planta 160 (1984), S. 12-20 
    ISSN: 1432-2048
    Schlagwort(e): Calcium ; Calmodulin ; Germination (spore) ; Onoclea ; Phytochrome and Ca2+ ; Pteridophyta
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Phytochrome is confirmed to be the photoreceptor pigment in the germination response of Onoclea sensibilis L. by demonstrating red-far-red (R-FR) photoreversibility. External Ca2+ is required for this response with a threshold at a submicromolar concentration. Ethylene glycol-bis(β-amino-ethyl ether)-N,N,N′,N′-tetraacetic acid, La3+ and Co2+ reversibly inhibit germination. Lanthanum only inhibits germination when applied before or during irradiation, indicating that the external Ca2+ requirement is transient, although in the absence of Ca2+ the R-stimulated system remains maximally poised to accept the ion for over 4 h after irradiation. The ability to respond to Ca2+ 4.1 h after R-irradiation is not reversed by FR-irradiation, indicating that Ca2+ transport has been uncoupled from phytochrome. Barium and Sr2+, but not Mg2+ can substitute for Ca2+. Artificially increasing the concentration of intracellular free Ca2+ with the ionophore A 23187 stimulates germination in the dark. The Ca2+-calmodulin antagonists, trifluoperizine and chlorpromazine, reversibly inhibit germination. Calcium is required in phytochrome-mediated fern spore germination; it may be acting as a second messenger.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Journal of molecular evolution 21 (1984), S. 19-32 
    ISSN: 1432-1432
    Schlagwort(e): Leghemoglobin ; Gene duplication ; Gene linkage ; Concerted evolution ; Nitrogen fixation ; Soybean
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary We have analyzed the sequences of soybean leghemoglobin genes as an initial step toward understanding their mode of evolution. Alignment of the sequences of plant globin genes with those of animals reveals that (i) based on the proportion of nucleotide substitutions that have occurred at the first, second, and third codon positions, the time of divergence of plant and animal globin gene families appears to be extremely remote (between 900 million and 1.4 billion years ago, if one assumes constancy of evolutionary rate in both the plant and animal lineages) and (ii) in addition to the normal regulatory sequences on the 5′ end, an approximately 30-base-pair sequence, specific to globin genes, that surrounds the cap site is conserved between the plant and animal globin genes. Comparison of the leghemoglobin sequences with one another shows that (i) the relative amount of sequence divergence in various coding and noncoding regions is roughly similar to that found for animal globin genes and (ii) as in animal globin genes, the positions of insertions and deletions in the intervening sequences often coincide with the locations of direct repeats. Thus, the mode of evolution of the plant globin genes appears to resemble, in many ways, that of their animal counterparts. We contrast the overall intergenic organization of the plant globin genes with that of animal genes, and discuss the possibility of the concerted evolution of the leghemoglobin genes.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 112 (1981), S. 149-156 
    ISSN: 1434-4475
    Schlagwort(e): Calcium ; Gallium ; Oxygen ; Single Crystal ; X-Ray
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The hitherto unknown compound Ca3Ga4O9 was prepared and investigated by X-ray single crystal methods. Ca3Ga4O9 has orthorhombic symmetry:a=1435.8;b=1682.5;c=532.1 pm; space group C 2v 11 −Cmm2,Z=6. The tetrahedra network (circles of 4 and 5 GaO4-tetrahedra) and the surrounding of Ca2+ are described and discussed with respect to other oxogallates.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 33 (1981), S. 365-368 
    ISSN: 1432-0827
    Schlagwort(e): Absorptiometry ; Osteoporosis ; Spinal bone ; Bone mineral content ; Neutron activation ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Dual-photon absorptiometry using153Gd (44 and 100 keV) was used to measure the bone mineral content (BMC) of the trunk and of the total body (TBBM) in 7 volunteers with no overt bone disease. These values were compared to those obtained with partial-body neutron activation of calcium (trunk Ca). The trunk Ca seemed to represent best a 60 × 30 cm area; the correlation coefficient with the corresponding BMC in that area was 0.97 (SEE ⋍ 7%). Trunk Ca was also highly correlated with TBBM (r=0.96; SEE=8%) and with radius BMC (r=0.92; SEE=11%), but the correlations with the BMC of smaller subareas of the trunk were lower (r⋍0.9; SEE ∼ 12%). The BMC of the lumbar spine was only moderately correlated with trunk Ca, radius BMC and TBBM (r ∼ 0.82; SEE ∼ 18%), and only slightly more associated with trunk BMC (r ∼ 0.88; SEE ∼ 14%). The BMC of the combined lumbar-thoracic spine showed higher correlations with trunk Ca, radius BMC and TBBM (r ∼ 0.87; SEE ∼ 13%), and trunk BMC (r=0.93; SEE ∼ 10%). An accurate and sensitive measure of spinal status requires a direct measurement of that area.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 22 (1977), S. 191-206 
    ISSN: 1432-0827
    Schlagwort(e): Bone ; Calcium ; Strontium ; Apposition ; Tracer analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract 1. Evidence has accumulated that the rate of acceretion (A) of calcium to bone is the sum of two fluxes; apposition involving the laying down of new bone and augmentation which is the result of slow exchange of non-surface bone calcium with plasma calcium pools as the result of solid state diffusion. 2. A method has been devised for separating A into its two components. It requires the use of45Ca or, for clinical studies,85Sr as a calcium tracer. Studies which are initiated with a combined accretion rate-calcium balance study, are concluded with an estimate of the exponent of the power function which has been found to describe the whole body retention of tracer from the second month onward. 3. The impulse response function of the skeleton for the tracer is then calculated, making the assumption that in any uniform volume of bone, osteoclastic resorption is a first order process. Making in addition certain simplifying assumptions, which are shown to have a modest influence on the final results, a mean rate of bone resorption can be calculated using a development of the well known Stewart-Hamilton formula. The apposition rate is calculated as the sum of the resorption rate and the calcium balance. Augmentation and diminution, defined as equal and opposite exchange processes, are given by the difference between A and the apposition rate. 4. The results of our first thirteen studies in normal subjects and patients with metabolic bone disease are presented, together with analyses of some data from the literature. It is concluded that the development of an atraumatic method for measuring rates of bone formation and resorption in the whole body would be an important advance in the study of metabolic bone disease, and this work is presented so that critical comparisons may be initiated between this tracer method and independent histological methods for measuring these parameters.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 26 (1978), S. 199-202 
    ISSN: 1432-0827
    Schlagwort(e): Fluoride ; Calcium ; Phosphate ; Parathyroid hormone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Fluoride 27 mg was given perorally to 14 subjects. It was found that the serum fluoride concentration increased followed by a decrease to normal levels during 24 h. Serum concentrations of calcium and phosphate decreased initially whereas those of serum immunoreactive parathyroid hormone increased. After 24 h the measured quantities were within normal limits. The results are discussed with reference to mineralization of hard tissues and to fluoride treatment of osteoporotic patients.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    ISSN: 1432-0827
    Schlagwort(e): Solanum malacoxylon ; Vitamin D metabolites ; Rickets ; Phosphate ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The effects of a partially purified aqueous extract ofSolanum malacoxylon (SM) leaves and of an SM extract incubated with ruminal fluid (RF) prior to administration on intestinal phosphate and calcium absorption in rachitic rats were compared with 1α, 25-dihydroxy-vitamin D3[1α,25-(OH)2-D3] using a duodenal loop in situ method. The time course responses elicited by both extracts were qualitatively similar to that of 1α, 25-(OH)2-D3. However, a single dose of SMRF was significantly more effective in stimulating32P absorption than an equivalent dose of SM. Part of this difference can be accounted for by incomplete saturation of the phosphate transport system with the level of SM employed. Treatment with rumen potentiated the effects of SM on45Ca absorption to a lesser extent. Extraction of SMRF with nonpolar organic solvents and purification of the lipid extract by chromatography on Silica Gel G thin-layer plates and on Sephadex LH-20 columns yield two fractions which promote intestinal32P absorption. The bioactive fraction eluting first from the Sephadex LH-20 column migrates similarly as 1α,25-(OH)2-D3. The greater effectiveness of SMRF extracts on intestinal phosphate and calcium absorption may be tentatively attributed to the release of 1α,25-(OH)2-D3 from the corresponding glycoside, shown previously to be present in SM, and to steroid modification during incubation with rumen.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 28 (1979), S. 17-22 
    ISSN: 1432-0827
    Schlagwort(e): Anticonvulsant ; Ketogenic diet ; Calcium ; Vitamin D ; Bone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Vitamin D and mineral metabolism status was examined in five children maintained chronically on combined ketogenic diet-anticonvulsant drug therapy (KG), and the results compared to those obtained in 18 patients treated with anticonvulsant drugs alone (AD) and 15 normal controls. KG patients exhibited biochemical findings of vitamin D deficiency osteomalacia: decreased serum 25-hydroxyvitamin D (25OHD) and calcium concentrations, elevated serum alkaline phosphatase and parathyroid hormone concentrations, decreased urinary calcium and increased urinary hydroxyproline excretion, and decreased bone mass. Although the KG and AD groups demonstrated similar reductions in serum 25OHD concentration, the KG patients exhibited a significantly greater reduction in bone mass. In response to vitamin D supplementation (5000 IU/day), mean bone mass in the KG group increased by 8.1±0.9% (P〈0.001) over a 12-month period. These results suggest that ketogenic diet and anticonvulsant drug therapy have additive deleterious effects on bone mass and that these effects are partially reversible by vitamin D treatment.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 28 (1979), S. 131-136 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Phosphate ; Citrate ; Precipitation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The influence of citrate ions on the precipitation of crystalline apatitic precipitates with low Ca/P molar ratios [octacalcium phosphate (OCP) and calcium-deficient apatites (DA) (system A)] and of the intercrystalline mixtures of calcium hydrogen phosphate dihydrate (DCPD) and DA (system B) was investigated. Samples were prepared by direct mixing of calcium chloride solutions (A, 6·10−3 mol dm−3; B, 1·10−1 mol dm−3) and sodium phosphate solutions (A, 6·10−3 mol dm−3; B, 2·10−2 mol dm−3) containing citrate (0–2·10−3 mol dm−3) and preadjusted to pH 7.4. In the presence of citrate ions: (a) crystal growth of OCP and DA was slowed down; (b) habit modification of DCPD crystals occurred; and (c) equilibration in intercrystalline mixtures of DCPD and DA's was slowed down. All phenomena were caused by surface adsorption of negatively charged ions, most probably CaC6H5O7-, which is the prevalent calcium citrate species under the given experimental conditions. Habit modification of DCPD was induced by preferential adsorption at the (001) crystal plane.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 29 (1979), S. 155-161 
    ISSN: 1432-0827
    Schlagwort(e): Periosteal cells ; Calcium ; PTH ; CT ; Metabolic inhibitors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Calcium transport was studied in cells isolated from cultured periostea of 18-day-old chick embryos. Net calcium uptake was stimulated by iodoacetate (IAA) and inhibited by dinitrophenol (DNP). Calcium efflux from the intracellular compartment was inhibited by IAA. Changes in the extra-or intracellular sodium concentration had only minor effects on calcium transport. This indicates that calcium efflux from periosteal cells is probably directly dependent on ATP hydrolysis, whereas calcium-sodium exchange is of less importance. The cation ionophore A23187 stimulated calcium uptake during short incubations but was inhibitory in long incubations. The possible involvement of the mitochondria in this effect is discussed. Parathyroid hormone (PTH) and calcitonin (CT) stimulated the net uptake of calcium in relatively low doses (both 0.01 U/ml or higher). The effects of the hormones on net calcium uptake were not additive. Calcium efflux was not changed in the presence of PTH or CT.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 30 (1980), S. 209-216 
    ISSN: 1432-0827
    Schlagwort(e): Calvarium ; cAMP ; Vitamin D3 metabolites ; Calcium ; Parathyroid hormone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Results from in vitro works suggest that 1,25- and 24,25-dihydroxyvitamin D3 (1,25-(OH)2D3 and 24,25-(OH)2D3) act on bone via different mechanisms. The present investigation was performed to study the effect of these two metabolites and of their precursor 25-hyxdroxyvitamin D3 (25-(OH)D3) on bone cAMP content in vitro. Rats' paired half calvaria were incubated under sterile conditions with one vitamin D3 derivative (10−13 to 10−9 M) or with ethanol (0.005 ml for 15 min to 24 h in 1 ml medium containing 0, 0.2, 1, 2, or 3 mM calcium. In some experiments: (a) cycloheximide (10−5M) was added simultaneously with the vitamin D3 metabolites; (b) 1–84 bPTH (5 × 10−8 M) was added for 5 or 15 min at the end of the 24 h incubation. Calvaria were immersed in 1 ml TCA 5% 4°C and homogenized. The cAMP was extracted with diethylether and measured by a competitive protein binding assay. Results bring further evidence for a particular effect of low doses of 24,25-(OH)2D3 (10−9 to 10−12M) and of 25-(OH)D3 (10−9 to 10−11M) on bone, different from that of 1,25-(OH)2D3: cAMP content was higher in 24,25-(OH)2D3- or 25-(OH)D3-treated and lower in 1,25-(OH)2D3-treated calvaria than in ethanol-treated ones with 1 mM calcium. The 1,25-(OH)2D3 effect persisted in calcium-free medium whereas 25-(OH)D3 and 24,25-(OH)2D3 effects could not be observed with 0 mM nor with 3 mM calcium. The required duration of the preincubation (over 1 h) as well as the inhibitory action of cycloheximide may suggest an involvement of protein synthesis in the vitamin D3 metabolites effects. Neither 1,25-(OH)2D3 nor 24,25-(OH)2D3 affected the PTH-induced increase in bone cAMP content.
    Materialart: Digitale Medien
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  • 21
    ISSN: 1432-0827
    Schlagwort(e): Hydroxyapatite ; Dissolution ; Pyrophosphate, Diphosphonates ; Calcium ; Phosphate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Pyrophosphate and diphosphonate ions have been said to diminish the dissolution of hydroxyapatite crystals, because they lower the equilibrium concentrations of calcium and phosphate ions in the bulk solution around hydroxyapatite crystals in a closed system. However, in a closed system these effects are not necessarily due to an effect on dissolution alone. In this paper we have used a continuous flow system to study the effects of pyrophosphate and two diphosphonates, ethane-1-hydroxy-1,1-diphosphonate and dichloromethane diphosphonate, on the dissolution of hydroxyapatite. All three compounds decreased markedly the rate of dissolution of hydroxyapatite as well as the exchangeable pools of calcium and phosphate ions around the cystals.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 31 (1980), S. 231-238 
    ISSN: 1432-0827
    Schlagwort(e): Magnesium ; Bone ; Calcium ; Parathyroid gland
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Calcium homeostasis and bone pathology were studied in weanling rats fed a low (70 ppm) magnesium diet for 2–21 days. The rats developed significant, progressive hypercalcemia after 6 days on the diet. The increase in blood calcium was accompanied by progressive hypoactivity of the parathyroid gland (PTG), as determined by histologic and morphometric analyses. Thus hyperactivity of the PTG could not have been responsible for the hypercalcemia observed. Histologic examination of femora and humeri from magnesium-deficient rats showed progressive subperiosteal hyperplasia, consisting of undifferentiated osteoprogenitor cells and fibrous tissue, after 7 days of deficiency. The presence of unmineralized osteoid tissue in the metaphyses indicated that mineralization was not proceeding normally. The alterations in differentiation of osteoprogenitor cells, together with the failure of mineralization, resulted in significantly lower rates of bone formation (as measured by fluorochrome labeling) in the magnesium-deficient rats. Basophilic cementing lines and inactive osteocytes in the cortices of bones from magnesium-deficient rats indicated that bone resorption was also severely reduced in magnesium deficiency. We postulate that bone magnesium depletion (66% by day 21) has a direct negative effect on osteoblastic and osteocytic activity, and may explain, in part, the decreased responsiveness of bone to parathyroid hormone (PTH) that has been observed in magnesium-deficient animals.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 32 (1980), S. 45-53 
    ISSN: 1432-0827
    Schlagwort(e): Dentin ; Periodicity ; Allometry ; Calcium ; Sulfur
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary We have described differences in the aspects of biological rhythms for calcium and sulfur deposition on the labial and lingual sides of the growing rabbit incisor, where growth occurs along a spiral axis. The calcium oscillations appear to be smoother on the labial side than on the lingual side. The lingual side is characterized by high-frequency rhythms with high amplitudes which possess the greatest percent of the power (Fourier analysis). These observations also reflect a difference in behavior of the mean Ca concentration across the labial and lingual sides. Sulfur rhythms on the labial side have higher amplitudes than those on the lingual side, but systematic differences in distribution of power between high and low frequencies is not as pronounced as in the case of Ca. The differences in Ca rhythms reflect differences in the growth rates of incisors on either side of the spiral axis. The labial side grows slightly faster than the lingual side, and its odontoblasts secrete Ca along the spiral axis and toward the pulp cavity at the same time. Thus the resultant direction of growth is more nearly opposite the extension of the occlusal end on the labial side, and Ca is consequently deposited over a wider area relative to that on the lingual surfaces. On the lingual side, Ca is deposited within a more limited area, and growth must therefore be continuous at high frequencies. The distribution of Ca on both sides of the tooth reflects these differences in growth rate and periodicity in two ways. First, given a unit area of tooth, the calcium concentration on the labial side is less than that of the lingual side. Second, whereas the calcium concentration on the labial side declines rapidly from the enamel-dentin junction to the pulp cavity, it is uniformly high across the lingual side because its growth is more continuous at high frequencies.
    Materialart: Digitale Medien
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  • 24
    ISSN: 1432-0827
    Schlagwort(e): 1α-Hydroxy vitamin D3 ; 1,25-Dihydroxyvitamin D3 ; Calcium ; Transport ; Intestine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The timed sequence of events following the oral administration of 1α-hydroxy vitamin D3 (1αOHD3) to rachitic chicks was compared to that following a comparable dose of 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). RNA polymerase activity was maximally increased 20% by 1αOHD3 within 1 to 2 h and returned to control values after 8 h. Alkaline phosphatase activity was stimulated by 4 h and was maximal (3- to 5-fold increase) at 24 h. Calcium binding protein (CaBP) was detected initially within epithelial cells at the proximal end of the villus (just above the crypt) 6 to 8 h after 1αOHD3 administration, in epithelial cells lining the proximal half of the villus by 24 h, and in epithelial cells along nearly the entire villus by 48 h. At no time did goblet cells contain CaBP. Serum calcium concentrations were significantly elevated in 2 h and maximal by 12 h (an increase of 3.6 mg/dl). Calcium accumulation by the intestinal mucosa in vitro was increased by 6 to 8 h and maximal (60% increase over controls) at 24 h. Phosphate accumulation by the intestinal mucosa in vitro was increased by 6 h and maximal (105% increase over controls) between 8 and 24 h. 1,25(OH)2D3 increased CaBP and calcium accumulation by 4 h, 2 h sooner than did 1αOHD3. 1,25(OH)2D3 decreased serum calcium levels and increased serum phosphate levels at 2 h unlike 1αOHD3. No difference in the effects of these compounds on alkaline phosphatase activity, RNA polymerase activity, and phosphate accumulation could be demonstrated. These results are consistent with the possibility that 1αOHD3 may not require conversion to 1,25(OH)2D3 for all of its biological effects.
    Materialart: Digitale Medien
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  • 25
    ISSN: 1432-0827
    Schlagwort(e): Perifusion ; Parathyroid hormone ; In vitro ; Calcium ; Beta regulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary An in vitro perifusion system was used to study parathyroid hormone (PTH) secretion in response to calcium (Ca) and beta-adrenergic agents. Perifused parathyroid tissue responded to changes in Ca within the physiologic range during experiments up to 5 h. There was rapid secretory stimulation after exposure to low Ca, with the maximum response being observed at 20 min. Normal bovine glands showed a Ca-independent nonsuppressible component of PTH release at concentrations of Ca above physiologic. 1-isoproterenol produced rapid stimulation of PTH release, the response being blocked by a beta antagonist. The maximum secretory response to either low Ca (0.5 mM) or 1-isoproterenol (10−5 M) was enhanced when the two stimuli were applied simultaneously. The response to isoproterenol was blocked by raising Ca to 2.5 mM. Although d,l-propranolol (10−4 M) caused mild suppression of PTH release at a Ca of 1.25 mM, it did not cause additional suppression at 2.5 mM Ca nor did it decrease the response to 0.5 mM Ca stimulation. The secretory response of the gland to low Ca was sustained at a level more than double the baseline rate. The response to isoproterenol was more transient, with a return to or toward baseline secretion within 60 min. These results suggest that beta agonists and low Ca have separate but related mechanisms for stimulating PTH release and may affect different pools of hormone. The perifusion system described is a relatively simple technique for assessing the kinetics and interactions of various stimulators of PTH secretion.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 32 (1980), S. 29-44 
    ISSN: 1432-0827
    Schlagwort(e): Rabbit ; Dentin ; Calcium ; Sulfur ; Periodicity ; Circadian ; Ultradian
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary We have identified a variety of biological rhythms involved in the apposition and mineralization of dentin in the rabbit incisor. Animals were injected during the day or night with lead acetate at 2-week intervals—to provide biological time markers in forming dentin—and transverse undecalcified sections of the lower incisors were prepared for electron microprobe analysis. The positions of the lead markers were identified, and the continuous distribution of calcium and sulfur was measured at 1 µm intervals between the markers. In thin sections stained with hematoxylin after decalcification, the widths of a series of structural increments (bands) were measured with an ocular micrometer. Fourier analysis of the data revealed spectra of structural and compositional rhythms with a range of periodicities which extended from a matter of hours [ultradian (〈24 h)] to days [infradian (〉24 h) and circadian (approximately 24 h)]. The structural and compositional rhythms appeared to be independent to the extent that they did not necessarily have the same periods, or amplitudes. Nor were there simple phase relationships between all of the rhythms. At some times, Ca and S fluctuations are inversely proportional (180° out of phase), but in other cases they are directly proportional or out of phase by varying degrees other than 180°. The analyses thus suggest that calcium and sulfur deposition (representing mineral and glycosaminoglycan deposition, respectively) are not simply inversely proportional, and that the hematoxylin-stained structural increments did not solely reflect differences in the distribution of the mineral components in dentin.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 34 (1982), S. 253-257 
    ISSN: 1432-0827
    Schlagwort(e): Prednisolone ; Calcium ; Bone ; Corticoid osteopenia ; Vitamin D metabolites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Adult male rats were fed a diet containing 0.15% calcium, 0.3% phosphorus, and either 100, 50, or 20 mg of prednisolone per kg of diet. All these levels of prednisolone led to osteopenia, decreased intestinal absorption of calcium, slightly lower serum calcium and phosphorus, and a decreased level of serum 1,25-dihydroxyvitamin D3. Exogenous parenteral 1,25-dihydroxyvitamin D3 corrected steroid-induced changes in serum calcium and phosphorus, but could not completely correct the low intestinal calcium transport; nor did it prevent the development of osteopenia. The prednisolone-induced osteopenia seems at least in part to be caused by impaired intestinal calcium transport. The impaired calcium transport may be the result of low levels of 1,25-dihydroxyvitamin D3 and a direct effect of presnisolone on the intestine.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 35 (1983), S. 107-110 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Glucocorticoid ; Vitamin D ; Osteoporosis ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Eighty-eight adult male Sprague-Dawley rats were given a diet with either (a) 0.5% Ca and 0.6% P or (b) 0.01% Ca and 0.6% P. Osteopenia was created by adding prednisolone to the diet. The prophylactic effect of oral 1,25(OH)2D3 on the osteopenia was studied. It was found that prednisolone osteopenia in the rat was associated with defective Ca absorption. By giving an oral dose of 1,25(OH)2D3, it was possible to maintain normal Ca absorption during prednisolone treatment and to prevent the bone loss. No significant hypercalcemia or any kidney calcifications were seen. These results are in contrast to earlier findings, in which subcutaneous administration of 1,25(OH)2D3 failed to prevent prednisolone osteopenia because of its tendency to increase bone resorption.
    Materialart: Digitale Medien
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  • 29
    ISSN: 1432-0827
    Schlagwort(e): 31P NMR spectroscopy ; Phosphoprotein ; Dentin ; Calcium ; Inorganic orthophosphate ; Bovine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The single phosphoprotein of fetal calf dentin, having a molecular weight of approximately 94,000 and a phosphorus content of 8% (w/w), was examined by31P NMR spectroscopy. The single resonance at 3.7 ppm at pH 10 and its chemical shift during acid titration established the phosphomonoester nature of the organic phosphorus moiety. During titration of the phosphoprotein with CaCl2 in the presence of inorganic orthophosphate ions, line broadening for the orthophosphate resonance was both phosphoprotein- and calcium-dependent, indicating ternary complex formation. The data indicate that the phosphoprotein of fetal calf dentin binds both calcium and inorganic orthophosphate ions and therefore has the requisite physical chemical properties necessary for it to facilitate the heterogeneous nucleation of a Ca-PO4 solid phase from solution during tissue mineralization.
    Materialart: Digitale Medien
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  • 30
    ISSN: 1432-0827
    Schlagwort(e): Calcitonin ; Parathyroid hormone ; Calcium ; Newborn ; Fracture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Determinations of serum calcium (Ca), phosphorus (P), calcitonin (CT), and parathyroid hormone (PTH) were carried out in 36 full-term newborn infants with fracture of the clavicle (CF) and in 46 normal neonates (N). At the 6th hour of life the CF neonates demonstrated lower serum Ca and higher serum CT in comparison with normal infants. In the hours following, no significant differences between the two groups for the Ca levels were found, whereas serum CT remained significantly higher in the CF newborns at the 24th, 48th, and 72nd hour of life. Significant differences between normal and CF infants in the PTH serum levels were detected only at the 48th hour, when PTH was lower in the CF newborns. The results of this investigation indicate that the fracture of the clavicle is a significant and peculiar factor in stimulating CT secretion. Serum Ca level appeared to be controlled by CT rather than auto-regulating the secretion of the hormone.
    Materialart: Digitale Medien
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 33 (1981), S. 409-416 
    ISSN: 1432-0827
    Schlagwort(e): Bone Cells ; Cyclic AMP ; Calcium ; Parathyroid hormone ; Prostaglandin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary We have examined the influence of extracellular Ca2+ on cyclic AMP metabolism in an osteoblast-enriched population of bone cells isolated from the calvaria of rat fetuses. The cyclic AMP1 response to stimulators of cyclic AMP formation (PTH and PGE2), but not basal cyclic AMP levels, increased progressively as the extracellular Ca2+ concentration was raised from 0.2 to 4.0 mM. The response to changes in extracellular Ca2+ were rapid (within 3.5 min), and the level of responsivity that characterized each Ca2+ concentration persisted for at least 6 h when the Ca2+ concentration was kept constant. The effect of Ca2+ spanned the entire time course of PTH action, was not accompanied by altered excretion of cyclic AMP from the cells, and was evident at low as well as at high hormone concentrations. Ca2+ augmented the action of PTH in the presence as well as in the absence of cyclic AMP phosphodiesterase inhibitors, and failed to decrease cyclic AMP phosphodiesterase activity in the short term. Mn2+ and, to a smaller degree, Ba2+ substituted for Ca2+ in promoting the cyclic AMP response to PTH. Verapamil, an inhibitor of Ca2+ penetration, blunted the Ca2+-mediated increments in the cyclic AMP response, and the divalent cation ionophore A23187 enhanced these increments. These results indicate that Ca2+ and other cations are positive effectors of the stimulated cyclic AMP response in isolated bone cells. Accumulation into an as yet unknown cellular compartment may be required for the cation effect. The data are most consistent with enhancement of adenylate cyclase reactivity as the mode of cation action.
    Materialart: Digitale Medien
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 22 (1977), S. 183-189 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Strontium ; Bone ; Mathematical modelling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract 1. A method has been devised for comparing the impulse response functions of the skeleton for two or more boneseeking tracers, and for estimating the contribution made by measurement errors to the differences between any pair of impulse response functions. 2. Comparisons were made between the calculated impulse response functions for47Ca and85Sr obtained in simultaneous double tracer studies in sixteen subjects. Collectively the differences between the47Ca and85Sr functions could be accounted for entirely by measurement errors. 3. Because the calculation of an impulse response function requires fewera priori assumptions than other forms of mathematical analysis, and automatically corrects for differences induced by recycling of tracer and non-identical rates of excretory plasma clearance of tracer, it is concluded that differences shown in previous in vivo studies between the fluxes of*Ca and*Sr into bone can be fully accounted for by undetermined oversimplifications in the various mathematical models used to analyse the results of those studies.85Sr is therefore an adequate tracer for bone calcium in most in vivo studies.
    Materialart: Digitale Medien
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 24 (1977), S. 275-278 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Thyroid ; Calcium ; Thyroïde
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Beschreibung / Inhaltsverzeichnis: Résumé Les auteurs utilisent une solution de Glyoxal bis 2-hydroxyanil à basse température pour localiser le calcium dans la thyroïde. Grâce à cette technique qui limite les mouvements ioniques, ils observent que le calcium situé principalement dans la colloïde est résorbé en même temps qu'elle lors d'une stimulation par le froid.
    Notizen: Summary With a Glyoxal bis 2-hydroxyanil alcoholic solution at −25°C, the calcium was localized in frozen thyroid slices. The limited ionic movement permits seeing that the calcium situated principally in the colloid is resorbed at the same time by a low temperature stress.
    Materialart: Digitale Medien
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 22 (1977), S. 275-284 
    ISSN: 1432-0827
    Schlagwort(e): Bone ; Calcium ; Collagen ; Dentine ; Phosphoprotein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract Calcium-binding and biochemical studies have been applied to characterize the state of the carboxylate and protein-bound phosphate groups in the EDTA-demineralized matrices of rat bone and dentine. The organic phosphate and carboxylate content of demineralized bone is virtually identical to that of purified steer skin collagen whereas demineralized dentine has a significantly higher phosphate and carboxylate content, presumably due to the presence of an acidic non-collagenous phosphoprotein. Two classes of calcium-binding sites can be detected in demineralized bone, demineralized dentine, and purified, reconstituted collagen. The number of strong calcium-binding sites correlates with the number of protein-bound phosphate groups. Depending on the preparative procedure, seven to nine such sites (per collagen molecule) are present in dentine, and one to two in the purified reconstituted collagen and in bone. The binding constant for the dentinal sites (1.1×104 M−1), however, is 20 times greater than that for bone or reconstituted collagen fibrils from skin. We tentatively conclude that the strong calcium-binding site in bone and reconstituted collagen is of the form protein-PO 4 − Ca++ whereas in dentine it is of the form the weak binding sites in bone and dentine are of the form protein-COO-Ca++; and that approximately 160 of the 217 carboxylate groups of the collagen molecules of dentine or bone are present as electrostatic linkages of the form protein-COO−+H3N-protein.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 23 (1977), S. 87-94 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Osteoporosis ; Lactation ; Chemistry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The calcium homeostatic mechanism was challenged in adult female rats by feeding them a calcium-deficient diet containing oxalate, and by subjecting them to pregnancy and lactation. The regimen caused a substantial weight loss, especially in those animals which reared their young well. Severe hypocalcaemia was observed in the lactating rats. Serum-P was slightly elevated. The content of hydroxyproline in serum was considerably elevated, reflecting the degree of calcium deprivation. Serum proteins were least influenced. The calcium depriving regimen reduced the growth of long bones, but did not stop it. The ash content of the bones was considerably reduced, the degree of reduction depended on the degree of calcium deprivation. Ash as percentage of total bone organ was reduced, but not to the same extent as total ash. Analyses of different parts of femur showed that the proximal and distal parts had lost more bone mineral than the diaphyseal shaft. The ash content of cortical bone tissue from the femur was estimated by a volumetric method. No differences were observed between test groups and controls, indicating that no measurable amounts of bone mineral had been removed from the walls of the vascular canals or by osteocytic osteolysis. Planimetric determinations on cross sections from femora disclosed that a great amount of bone had been removed from the endosteal surface of the diaphysis, while the periosteal surface demonstrated reduced bone apposition.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 26 (1978), S. 39-45 
    ISSN: 1432-0827
    Schlagwort(e): Solanum malacoxylon ; Bone culture ; Resorption ; Calcium ; Osteoclasts
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The water-soluble active principle of the plantSolanum malacoxylon (SM) was partially purified by column chromatography, and its bone-resorbing activity was tested by using an organ culture system of 18-day fetal mouse fibulae prelabeled with45Ca. Three series of experiments were performed. In the first series, the aqueous extract of SM was submitted to Sephadex G-25 chromatography to separate the active substances. From six collected fractions only two exhibited reproducible bone-resorbing activity as indicated by an increased release of45Ca from bone rudiments. In the second series, the active fractions were combined and lyophilized to a powder which was dissolved in the culture media to obtain the concentrations of 5, 25, 50, and 100 μg/ml. The addition of this saltfree material resulted in a dose-related accentuation of45Ca release from fetal mouse bones into the medium. Histologically, the treated fibulae showed greater numbers of osteoclasts than the controls and a disappearance of bone trabeculae. In the third series, the active material was further purified on Sephadex LH-20 column. From four collected fractions, only one showed bone-resorbing activity in vitro. It is concluded that the purified active factor of SM exerts a direct effect on bone. It stimulates the mobilization of bone calcium in vitro by increasing the population of osteoclasts. The nature of the active principle remains unknown.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 26 (1978), S. 71-79 
    ISSN: 1432-0827
    Schlagwort(e): Absorption ; Calcium ; Mitochondria ; Intestinal epithelium ; Potassium-pyroantimonate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Intracellular transport of calcium from the apical to the basal-lateral region of the intestinal epithelial cell was invetigated in duodenum from normal fed, fasted, and calcium-loaded rats. The process was followed with time using electron microscopy with potassium pyroantimonate to precipitate calcium. The observations made were subjected to morphometric analysis. The specificity of the method was demonstrated in the villus cell by resistance to micro-incineration and by absence of deposits following exposure to EGTA. Using this method calcium was seen in cells from calcium-fed rats at the microvillus border, in the Golgi zone, and within the internal compartments of the mitochondria. In cells from fasted rats calcium was not seen. Mitochondria were found largely at the apex of the cell and were free of detectable calcium. By 5 min, in the cells of fasted rats given a calcium load, the calcium had reached the Golgi apparatus and the inner mitochondrial compartment. After 15 min mitochondria were heavily loaded with calcium and had moved to the basal region of the cell. These observations suggest that mitochondria play an important role in absorption of calcium and appear to transport this ion from the apex to the basal region of the cell where entry into the capillaries takes place.
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 27 (1979), S. 171-176 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Phosphate ; Precipitation ; Double diffusion ; Collagen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary One-dimensional double diffusion was applied to determine critical concentrations at which the precipitation of calcium phosphates occurs in reconstituted connective tissue collagen and agar gels at 37°C and in gelatin gels at 25°C. Experiments were performed in the presence of unbuffered 0.15 mol dm−3 NaCl, or 0.15 mol dm−3 NaCl-veronal adjusted to pH 7.4. It was found that critical concentrations of precipitation of both precipitating components, CaCl2 and phosphate buffer (pH 7.4), were equimolar and independent of the ratios of initial concentrations of the components. Critical concentrations of precipitation were not affected by the concentrations and kinds of gels used. The first-formed precipitates showed amorphous structure by X-ray diffraction analyses. Infrared (IR) spectra of the precipitates indicated CaHPO4 · H2O to be their predominant species. The molar Ca/P ratio obtained by chemical analyses was 1.08. This precipitate transformed in time into octacalcium phosphate. In all experiments, two very thin membranes of precipitate were formed in the gel column at the onset of precipitation simultaneously on both sides of the actual disc of precipitate. IR spectra and chemical analyses showed that both membranes were identical to the actual precipitation discs.
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 25 (1978), S. 227-232 
    ISSN: 1432-0827
    Schlagwort(e): Parathyroid hormone ; Bone ; Calcium ; Chick embryo ; Organ culture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The purpose of this study was to measure in an in vitro system the movement of Ca and phosphate (Pi) out of bone when treated with parathyroid hormone (PTH). Tibiae from 13-day chick embryos were incubated for up to 8 h in a defined medium containing 1.8 mM Ca. Medium samples were collected every 2 h and were analyzed for Ca, Pi and lactate. Net effluxes from the bones were calculated. When bones were incubated with PTH in the medium (1 U/ml), net Ca efflux was increased 44, 60 and 100% at 4, 6 and 8 h, respectively. At no time was net Pi efflux affected by the hormone. The well known PTH-stimulated lactate production was not seen until 8 h. Lower doses of PTH (0.1 and 0.3 U/ml) were also effective. Comparing PTH (1 U/ml) responsiveness at higher (2.2 mM) and lower (0.9 mM) medium Ca concentrations, showed that with 2.2 mM Ca no increased Ca efflux was seen, while with 0.9 mM Ca significant elevation in medium Ca occurred 2 h sooner than in the experiments using 1.8 mM Ca. In another experiment, varying the medium Pi level from 1 to 2 mM had no effect on the Ca response to PTH. In neither experiment was Pi release affected by PTH. The results of this study have led to the following conclusions: (1) PTH acts on bone to cause an early dose related increase in net Ca efflux; (2) the effect is specific for Ca, since it is not accompanied by an increased Pi efflux, and may be saturated by raising the medium Ca level; and (3) PTH-stimulated Ca efflux in this system is not correlated with, and is probably not a result of increased lactate production.
    Materialart: Digitale Medien
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  • 40
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; PTH ; 1,25(OH)2D ; Acid ; Bone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary We measured mineral and acid balances, serum iPTH, urinary cAMP/creatinine, and plasma concentrations of 25OHD and 1,25(OH)2D in 7 healthy adults during control conditions and during increased fixed acid production achieved either by the administration of NH4Cl (N=3) or by increased dietary protein intake (N=4). When acid production was increased, the subjects were in positive acid balance and negative Ca balance because of increased urinary Ca excretion. Serum iPTH fell slightly but urinary cAMP and the plasma levels of vitamin D metabolites did not change. We conclude that the accelerated skeletal and urinary losses of Ca that occur when fixed acid production is increased are not contributed to nor compensated for by the parathyroid-vitamin D endocrine systems.
    Materialart: Digitale Medien
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 29 (1979), S. 63-69 
    ISSN: 1432-0827
    Schlagwort(e): Vaterite ; Calcium ; Eggshells ; Cuckoos
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The crystalline spherules occurring in patches on the outer surface of the eggshells ofGuira guira and the bloom on the entire outer surface of those ofCrotophagi ani were shown by X-ray diffraction analysis to be vaterite.
    Materialart: Digitale Medien
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 32 (1980), S. 201-206 
    ISSN: 1432-0827
    Schlagwort(e): Magnesium ; Parathyroid hormone ; Secretion ; In vitro ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary In a well-defined in vitro perifusion system, the effects of extracellular magnesium concentration (Mg) on parathyroid hormone (PTH) secretion by bovine parathyroid tissue were examined. At Mg less than 0.8 mM, the ability of the glands to secrete hormone maximally in response to low calcium (Ca) stimulation was progressively impaired. Low Mg also impaired the ability of isoproterenol, dibutyryl cyclic AMP and theophylline to stimulate hormone release. The defect in hormone release at low Mg observed in vitro was analogous to the well-documented inhibition of secretion observed in vivo. Increases in Mg from 0 to 0.8 mM rapidly repaired the defect in hormone secretion. At Mg above 1.0 mM there was a Ca-like effect on hormone release, with a progressive decrease in secretion at increased Mg. Although its mechanism is not yet clear, the low Mg effect appears to impair principally the process of hormone release rather than its biosynthesis or storage.
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 77-82 
    ISSN: 1432-0827
    Schlagwort(e): Osteogenesis ; Diffusion chambers ; Alkaline phosphatase ; Calcium ; Phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The alkaline phosphatase activity and the calcium and phosphorus content of osteogenic tissue formedin vivo following the implantation of diffusion chambers loaded with rabbit bone marrow cells is reported. (In this study the term osteogenic includes osteoblastic and chondroblastic.) Chambers examined 14–70 days after implantation revealed progressive accumulation of mineral. Alkaline phosphatase activity increased until day 30 and declined thereafter. The osteogenic potential of the marrow cells decreased with increasing weight (age) of the cell donor rabbit when measured either as the percentage of chambers containing osteogenic tissue or as the amount of calcium, phosphorus, or alkaline phosphatase activity within the chambers. The results confirm that measurements of these parameters in tissue formed by cells incubated in diffusion chambersin vivo may be used as a method for assay of osteogenesis.
    Materialart: Digitale Medien
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  • 44
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Vitamin D deficiency ; 1,25(OH)2D3 ; Parathyroidectomy ; Parathyroid hormone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Studies presented here were designed to investigate further the basis for an impaired cAMP response to parathyroid hormone (PTH) in osteoblastlike calvarial bone cells isolated from vitamin D-deficient rat pups. The goal was to perturb Ca, PTH, and vitamin Din vivo in order to see which factors might be responsible for the impairedin vitro bone cell cAMP response. Pups either were parathyroidectomized (PTX) 3–5 days, implanted with osmotic minipumps delivering high doses of PTH, given repeated, high doses of 1,25(OH)2D3, or were D-deficient (-D, i.e., born and suckled by D-deficient mothers). Osteoblastlike bone cells, isolated by sequential enzyme digestion and centrifugation, were exposed to PTH for 5 min in the presence of a phosphodiesterase inhibitor. In bone cells isolated from -D rat pups, both basal and PTH-induced cAMP accumulation were significantly lower than in +D bone cells. Earlier, we had shown that two daily injections of -D pups with 50 ng 1,25(OH)2D3 restores this reduced bone cAMP response of -D pups toward normal. In the present study, neither basal nor PTH-induced bone cell cAMP accumulation was affected by subjecting D-replete pups to PTX, PTH infusion, or repeated high doses of 1,25(OH)2D3 despite the fact that each treatment markedly changed serum Ca or serum immunoreactive PTH. The results indicate that the impaired bone cell cAMP response seen in -D pups is not a direct result of chronic hypocalcemia and that the “heterologous desensitization” seenin vitro with added 1,25(OH)2D3 could not be duplicated byin vivo treatment of +D pups with supraphysiologic doses of 1,25(OH)2D3. Finally the lack of alteration in the bone cell cAMP response to PTHin vitro after chronic PTH infusionin vivo fails to support the notion that the impaired response in -D bone cells can be explained entirely by “homologous desensitization” induced by high circulating levels of PTH in the hypocalcemic, -D rat pup.
    Materialart: Digitale Medien
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 33 (1981), S. 485-488 
    ISSN: 1432-0827
    Schlagwort(e): 1,25-(OH)2-D ; Hypophysectomy ; Calcium ; Phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The mechanism by which dietary phosphate deprivation elevates plasma 1,25-(OH)2-D levels is not known. To evaluate the role of the pituitary in regulating plasma 1,25-(OH)2-D concentrations, the responses of plasma 1,25-(OH)2-D to dietary phosphate deprivation and, separately, to dietary calcium deprivation were evaluated in intact and hypophysectomized male rats. Among intact and hypophysectomized rats eating normal diets, plasma 1,25-(OH)2-D levels averaged 228±76 and 148±62 pmol/1, respectively (P〈0.01). During dietary phosphate deprivation, plasma 1,25-(OH)2-D levels rose to 1160±260 in intact rats and fell to 90±26 pmol/l in hypophysectomized rats (P〈0.001). By contrast, during dietary calcium deprivation, plasma 1,25-(OH)2-D levels rose in both intact and hypophysectomized animals to 856±107 and 742±279 pmol/l, respectively (NS). In response to dietary phosphate deprivation, serum calcium concentrations rose as 1,25-(OH)2-D concentrations rose in intact rats but remained at control levels in hypophysectomized rats. These results support the hypothesis that a pituitary hormone acting either directly or indirectly on the kidney mediates the increase in plasma 1,25-(OH)2-D during dietary phosphate deprivation. The hypercalcemia that occurs in rats during dietary phosphate deprivation appears to depend on the elevation of plasma 1,25-(OH)2-D.
    Materialart: Digitale Medien
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 24 (1977), S. 59-64 
    ISSN: 1432-0827
    Schlagwort(e): Enamel ; Calcium ; Exchange ; Diffusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The penetration of45Ca ions into whole bovine enamel from an aqueous solution was studied as a function of the Ca content in the solution. A sectioning technique was employed to measure the penetration of45Ca into the enamel. Probably only Ca ions occupying surface positions in the hydroxyapatite crystallites participate in the exchange process at the solution-enamel interface. The fraction of Ca ions participating in the exchange was 2% of the total number of Ca ions. Two different diffusion processes occur; firstly, a process governed by a diffusion coefficient, D1 ranging from about 5×10−14 to 2×10−12 cm2/s and strongly dependent on the calcium concentration in the solutions; and secondly a process with a concentration-independent diffusion coefficient, D2, with a value of 2.8×10−12 cm2/s. It is assumed that the 2 diffusion types correspond to intra-and interprismatic transport, respectively. A model based on the pore structure of dental enamel and on surface charges on hydroxyapatite crystallites is discussed.
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  • 47
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 24 (1977), S. 113-117 
    ISSN: 1432-0827
    Schlagwort(e): Bone membrane ; Calcium ; Ion fluxes ; Calvarium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary To facilitate the study of membrane function in the control of the flow of ions into and out of bone, it was desirable to develop a system for the direct quantitation of unidirectional effluxes of calcium and phosphate from bones. Based on a mathematical analysis of the problem, a specially designed Ussing chamber was developed which proved successful. Calvaria from 2-day-old rat pups, 3-day chicks and adult mice were evaluated. Calcium influxes which exceeded the corresponding effluxes were observed in the neonatal calvaria but not with those from adult mice. Also, an asymmetry in efflux was observed in rat calvaria, the inner side of the skull showed a higher efflux than did the external side. no such asymmetry was seen with calvaria from chicks or mice. This new technology should permit a further exploration of the role of the bone membrane in electrolyte homeostasis.
    Materialart: Digitale Medien
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  • 48
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 22 (1977), S. 9-17 
    ISSN: 1432-0827
    Schlagwort(e): Bone ; Fluoride ; Calcium ; Phosphorus ; Mechanical Strength
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract Four groups of weanling rats were fed for 2 weeks on a diet sufficient or insufficient in calcium and/or phosphorus. Each group was divided into four subgroups which were offered distilled water supplemented with 0, 50, 75, or 150 ppm fluoride. High levels of fluoride in drinking water inhibited weight gain. This inhibition was less in rats deficient in phosphorus than when normal-phosphorus diets were offered. At a low level, fluoride was without any effect on bone ash, thickness of femoral cortical bone, and mechanical strength, as measured by maximal load, ultimate stress to breaking, and limit of elasticity. Modulus of elasticity was decreased. At higher levels fluoride tended to decrease most of these parameters, except in rats deprived of both calcium and phosphorus. The effect of fluoride was modified by lack of dietary calcium and/or phosphorus and appeared to be weaker in rats deficient in these nutrients. Lack of dietary calcium and/or phosphorus decreased bone strength more than did fluoride content of water and of bone mineral. Concentration of bone ash and thickness of femoral cortical bone were closely correlated with parameters of mechanical strength.
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 30 (1980), S. 27-34 
    ISSN: 1432-0827
    Schlagwort(e): Ultrastructure ; Calcium ; Cartilage ; Vesicles
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The potassium pyroantimonate technique was utilized for the selective subcellular localization of calcium in the mandibular condylar cartilage of 1-day-old rats. Electron dense calcium pyroantimonate precipitates were localized principally in mitochondria and at the cell membrane of the chondrocytes. In addition, small intracellular vesicles 0.1–0.2µm in diameter were observed in proximity to the cell membrane of chondrocytes of the mid-hypertrophic zone. The results suggest that these vesicles were being extruded from the cell into the extracellular matrix. Energy-dispersive analysis by X-rays confirmed that calcium is the principal cation of the electron-dense precipitates.
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  • 50
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 269-273 
    ISSN: 1432-0827
    Schlagwort(e): Bone loss (osteopenia) ; Calcium ; Corticosteroids (glucocorticosteroids) ; Fluoride ; Vitamin D
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary To evaluate the effect of prednisone and triple treatment (sodium fluoride, calcium, and vitamin D) on trabecular and cortical bone serial bone mineral content (BMC) measurements were made at a metaphyseal (BMCD) and diaphyseal (BMCP) site on the forearm on 31 consecutive and previously bone-healthy patients scheduled for at least 24 weeks high-dose prednisone treatment. The patients were randomized into two further treatment groups: group I (n=16) received prednisone plus triple treatment and group II (n=15) received only prednisone. The two groups were similar with regard to age, sex, prednisone dose, and initial BMC. During 24 weeks treatment, BMCD (partially representing trabecular bone) and BMCP (mainly representing cortical bone) fell significantly and similarly, demonstrating that there is no preventive effect on bone mineral loss on the triple regimen. The BMC fall after 12 weeks was significantly more pronounced for metaphyseal (partially trabecular) than for diaphyseal (cortical) bone, whereas the values did not differ significantly after 24 weeks; this indicates a greater sensitivity to the hormone treatment of trabecular bone. In the entire group, the fall in BMC correlated positively with individual prednisone dose, significant at the diaphyseal site (r=0.39,P〈0.05), but not at the metaphyseal site (r=0.31, P=0.08). It is concluded that corticosteroid-induced osteopenia is a diffuse bone disease which affects trabecular as well as cortical bone, suggesting that BMC measured on the forearm reflects changes in bone mineral at other locations.
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 392-400 
    ISSN: 1432-0827
    Schlagwort(e): Vitamin D ; Chick embryo ; Bone ; Calcium ; Phosphate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Chick embryos were injected in the yolk sac at various ages with various doses of different vitamin D3 metabolites. Serum concentrations of total calcium and inorganic phosphate were determined 24 h after the injection and histological and electron microscopic studies of the tibiae were conducted 3–6 days after. Confirming previous results, the injection of 1,25(OH)2D3 was found to produce significant hypercalcemia and hypophosphatemia. The dose required to produce these effects decreased with age: 100 ng on the 9th day, 50 ng on the 11th, and 10 ng on the 15th. This finding is interpreted as resulting from the fact that the specialized cells in the chorionic epithelium which are considered to be involved in mineral resorption from the shell differentiate between the 11th and 13th days. Although no bone changes were observed in embryos injected before the 11th day, a rim of unmineralized trabeculae (osteoid) was observed at the periphery of the cortex of the tibial diaphysis in the embryos which had been injected after that age. Thus, in embryos injected on the 11th day with 100 ng 1,25(OH)2D3, the trabeculae formed between the 11th and 14th day remained unmineralized until the 15th or 16th day at which time they completed their mineralization. In the embryos injected on the 14th day, the alterations were more severe and could be produced with doses 10 times smaller than those required when the injections were made on the 11th day. At all ages, the doses that produced an osteoid rim also induced hypercalcemia and hypophosphatemia. The electron microscopical study of the osteoid trabeculae showed that osteoblasts and osteocytes had normal cytological characteristics and that the bone matrix did not present changes other than the reduction in mineral deposition. While the above findings do not exclude a direct action of 1,25(OH)2D3 on bone cells as the mechanism of osteoid formation, they do underline the importance of the humoral changes at least as partial determinants of this phenomenon. The activities of various vitamin D metabolites were compared using as parameter the threshold-dose required to produce a rim of unmineralized trabeculae in the tibia of 14–15 days embryos (T-D). The most active metabolite appeared to be 1,25(OH)2D3 (T-D: 10 ng); it was followed by 1,24,25(OH)3D3 (T-D: 100 ng) and 1,25,26(OH)3D3 (T-D: 100 ng). Vitamin D3 itself (T-D: 100 µg), 25(OH)D3 (T-D: 2.5µg) and 24,25(OH)2D3 (T-D: 5 µg) produced similar responses but only when administered in much larger doses.
    Materialart: Digitale Medien
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  • 52
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 596-603 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Ameloblasts ; X-ray microanalysis ; Transport ; Frozen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Energy dispersive X-ray microanalysis was applied to freeze-dried blocks of enamel organ tissue to determine levels of calcium in various celular regions. The tissue blocks were dissected free from adjacent forming enamel following injection of cobalt or fluoride ions, both of which temporarily inhibit enamel mineralization. In all control and experimental specimens there was an increasing gradient of calcium from the stratum intermedium cells to the distal ends of the ameloblasts. Calcium levels were significantly reduced near the distal ends of the ameloblasts following cobalt or fluoride injection as compared with controls. It is suggested that evidence of an intercellular buildup of calcium near the distal ends of the ameloblast supports a controlling function of these cells. The changes in calcium levels are correlated with alterations in mineralization known to occur in the adjacent enamel of the model systems employed.
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  • 53
    ISSN: 1432-0827
    Schlagwort(e): Saliva ; Calcium ; Phosphate ; Ion-binding ; Supersaturation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Previous ultrafiltration studies indicated that up to one-half of the calcium and two-thirds of the phosphate in human salivary secretions may be bound by salivary proteins. Since this binding is an important variable in determining the extent of salivary supersaturation with respect to calcium phosphate salts, and since the amount of binding reported is surprisingly large, calcium and phosphate ion-binding by salivary macromolecules has been reexamined. From experiments using equilibrium dialysis, it was found that (1) the fraction of salivary calcium involved in macromolecular complexes ranges from a few percent for unstimulated secretions, to no more than about 10% for stimulated glandular salivas, and (2) salivary proteins do not bind phosphate ions to any significant extent. These findings, and experiments using an improved ultrafiltration membrane, indicate that the earlier results were artifacts of the ultrafiltration technique. Fractionation of salivary proteins, followed by equilibrium dialysis measurements, showed that the anionic proline-rich proteins and a basic proline-rich glycoprotein are responsible for most of the calcium binding now observed. The finding that macromolecular complexes of salivary calcium and phosphate have been overestimated in the past, leads to the conclusion that salivary calcium and phosphate ion activities in stimulated salivary secretions may be up to 50 to 100% higher than previously thought. Revised values were therefore used to recalculate the degree of salivary supersaturation with respect to calcium phosphate salts. The results indicate that stimulated salivary secretions are supersaturated with respect to dicalcium phosphate dihydrate; this is a substantially greater degree of supersaturation than previously reported.
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 33 (1981), S. 477-484 
    ISSN: 1432-0827
    Schlagwort(e): 1,25-(OH)2-D ; Calcium ; Phosphorus ; Sex ; Age
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Dietary phosphate deprivation in women, but not men, is accompanied by a fall in plasma PO4 and a rise in plasma 1,25-(OH)2-vitamin D concentrations. In contrast, young male rats exhibit a fall in plasma PO4 and a rise in plasma 1,25-(OH)2-D concentrations in response to PO4 deprivation. To evaluate whether age and sex influence basal plasma 1,25-(OH)2-D levels and their regulation by PO4 deprivation, plasma 1,25-(OH)2-D, PO4, and Ca levels were measured in male and female rats ranging in age from 6 weeks to 6 months while they were eating normal or low PO4 diets for 1 to 16 days. Similar observations were also made in 6-week-old castrated male and female rats, males replaced with testosterone, and females replaced with estradiol. Basal plasma 1,25-(OH)2-D levels were higher in 6-week-old males (228±76 pmol/l) than in 6-week-old females (148±62 pmol/l;P〈0.01) and declined by age 11 weeks to stable levels averaging about 100 pmol/l without sex difference. Dietary PO4 deprivation resulted in a three-to fourfold increase in plasma 1,25-(OH)2-D concentrations regardless of age and sex, accompanied by a correlated rise in serum Ca concentrations. Castration of 6-week-old males and females eliminated the sex difference in basal plasma 1,25-(OH)2-D levels and appeared to enhance the elevation of plasma 1,25-(OH)2-D concentrations in response to PO4 deprivation in females. Although gonadal hormones may modify basal plasma 1,25-(OH)2-D levels, they are not required for the augmentation of plasma 1,25-(OH)2-D levels in response to PO4 deprivation.
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  • 55
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 33 (1981), S. 575-581 
    ISSN: 1432-0827
    Schlagwort(e): Osteoporosis ; Vitamin D ; Bone mineral ; Estrogen ; Aging ; Thiazide ; Fluoride ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Bone mineral content (BMC) was measured by125I photon absorptiometry every 3 months in 264 normal females (45–54 years) over a 2-year period together with serum samples for calcium, phosphate, magnesium, creatinine, alkaline phosphatases, potassium, and protein. A 48-h urinary calcium and creatinine measurement was obtained. The subjects were divided into 7 treatment groups and 3 placebo groups. Five of the treatments (thiazide, vitamin D3, fluoride + vitamin D3, fluoride, and 1αD3) were ineffective at the doses used; the annual loss of compact bone was 1.5–2.2% (-X=1.8%), similar to the loss seen with placebos. Estrogen and estrogen + thiazide, in contrast, produced a 1.34% annual increase of BMC. The subjects were divided into groups with low, medium, and high initial BMC. Also, individual regressions for bone change were calculated and the subjects were divided into groups of responders, maintainers, and losers (annual change of 〉0%, 0 to −1%, and 〉−1%, respectively). The initial BMC status did not consistently affect bone or biochemical responses to the therapeutic agents. Estrogen was effective even in subjects with high BMC, whereas the other agents did not inhibit bone loss even in subjects with low initial BMC. Virtually all subjects responded to estrogen positively; in contrast we could not identify a subset of “responders” with any of the other treatments. Time since menopause appeared to influence the bone changes, although it was not a significant effect given the sample size. Bone loss in groups not treated with estrogens was 2%/year at 20 months after menopause with a decline to 1.3%/year at 45 months post-menopause. There was no apparent decline in the bone response to estrogen during the first 4 years after menopause, and in fact bone response tended to increase with time.
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  • 56
    ISSN: 1432-0827
    Schlagwort(e): Bone cells ; Cyclic AMP ; Calcium ; Ascites fluid resorptive protein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The effects of a bone resorptive protein isolated from human cancer ascites fluid on bone cell calcium and cyclic AMP were studied with fetal rat cells. The osteoclast-activating factor increased bone cell calcium uptake at 37°C and 4°C with no direct effects on calcium efflux. Concentrations of the resorptive factor that increased in vitro bone resorption and cell calcium uptake had no effect on cyclic AMP. The effects of the protein on calcium uptake were not specific for bone cells, and large increases were also observed in isolated fetal rat skin cells. These studies suggest that increases in the permeability of the cell membrane to calcium are involved in the mechanism of action of the ascites fluid resorptive protein.
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  • 57
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Intestine ; Growth ; Cortisol ; Hydroxyproline ; Parathyroid hormone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary This paper reports the effects of cortisol on intestinal management of calcium and on related changes on bone metabolism. Five groups of 12 rats each fed a standard diet (0.8% Ca) received 2, 6, 16, 32, and 128 mg/kg/day of cortisol hemisuccinate, subcutaneously. After 16 days, intestinal absorption and excretion of Ca were measured with the aid of45Ca. True Ca absorption increased as a function of dose up to 16 mg/kg/day and remained high with the larger doses. Endogenous fecal Ca excretion increased exponentially as a function of the dose from 16 mg/kg/day onwards. Therefore, a dual effect was observed: (a) an increase in true Ca absorption at low cortisol doses (which increased net Ca absorption); and (b) an increase in endogenous fecal Ca excretion at high doses (which reduced net Ca absorption). In no case was a depression of true Ca absorption observed. Growth rate and food conversion efficiency were depressed only with a cortisol dose of 128 mg/kg/day. The urinary excretion of hydroxyproline, pyrophosphate, and aminopolysaccharides decreased with low doses and increased above normal levels with the highest dose. When animals treated with 128 mg/kg/day of cortisol were fed Ca-enriched diets, net Ca absorption improved. Simultaneously, growth rate and food conversion efficiency approached normal values. In these experiments, net absorption of Ca was found to be inversely related to urinary excretion of hydroxyproline. The urinary rate of excretion of hydroxyproline is suggested as an indicator of the effect of a Ca supplement on cortisol affected connective tissue turnover.
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  • 58
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 24 (1977), S. 173-177 
    ISSN: 1432-0827
    Schlagwort(e): Enamel ; Calcium ; Diffusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The diffusion of45Ca ions in sound bovine enamel at pH 7.0 was studied as a function of temperature in the range 20°–40°C. The experimental data show that the diffusion is governed by two processes with activation energies of about 0.7 and 1.3 eV respectively. These values are considerably larger than the activation energy of calcium ion diffusion in water (0.2 eV). The diffusion process with the activation energy of 1.3 eV is dependent upon the calcium concentration in solution. A model based on the complex pore structure of enamel and on interactions of diffusing ions with the enamel constituents is discussed.
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  • 59
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 27 (1979), S. 205-210 
    ISSN: 1432-0827
    Schlagwort(e): Intestine ; Calcium ; Binding ; Protein ; Uremia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary In order to assess the usefulness of intestinal biopsies as indicators of end-organ responsiveness to vitamin D in uremic patients, calcium binding activity and calcium binding protein (CaBP) content were measured in intestinal biopsies from 12 uremic patients (glomerular filtration rate〈5.0 ml/min) and 12 adult controls. Values for both were found to vary with the site of biopsy, highest values being obtained in the duodenal bulb, with lower values distally. Values for activity correlated with values for CaBP content in both normals and uremics and no difference was observed between groups. Levels of calcium binding activity and content of CaBP did not correlate with serum immunoreactive parathormone levels, but were directly related to circulating 25-hydroxycholecalciferol (25-OHD) levels. The data show that intestinal CaBP is normal in activity, quantity, and affinity for calcium in malabsorbing uremic patients, and are consistent with the hypothesis that calcium malabsorption in uremia is unrelated to deficiency of intestinal calcium binding protein.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 27 (1979), S. 239-246 
    ISSN: 1432-0827
    Schlagwort(e): Parathyroid hormone ; Calcium ; Plasma phosphate ; Bone phosphate ; Plasma32P ; Specific activity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Plasma changes in calcium, phosphate, and their radionuclides were studied in thyroparathyroidectomized (TPTX) rats treated with parathyroid hormone (PTH) for 8 h, this treatment starting 10 h after injection of45Ca and32P. Prior to intravenous infusion or hourly injections of PTH (10 mU/g/h), rats were maintained in one of three ways: on an extended fast (24 h); on a partial fast (10 h); or provided with 10% glucose and 1% calcium lactate overnight as a substitution for solid food. The pattern of change for plasma calcium,45Ca, and45Ca specific activity (S.A.) produced by PTH was not affected by these dietary conditions. The changes in phosphate were as follows: During the experimental (8 h) period, the rate of loss of32P from plasma in control rats was proportional to the length of the fast. This suggests that32P was released into plasma during the experimental period proportional to the ready availability of soft tissue glucose. In rats on an extended fast, PTH was phosphaturic, hypophosphatemic, and increased the rate of loss of32P from plasma without affecting32P S.A. values. In rats fasted for only 10 h, PTH produced similar effects on plasma phosphate and plasma32P values, but also caused a significant fall in plasma32P S.A. After glucose and calcium lactate treatment, PTH-induced phosphaturia was temporarily lost and the marked hypophosphatemia was replaced with a slight hyperphosphatemia. Plasma32P values also rose slightly; therefore, no effect on32P S.A. was produced. It is concluded from these studies that as the result of the phosphaturia caused by PTH, the hypophosphatemia which is produced automatically changes the phosphate gradient between various body compartments, causing phosphate entry into plasma. The authors postulate that this phosphate entering plasma is withdrawn primarily from bone fluid and bone.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 61
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 24 (1977), S. 271-274 
    ISSN: 1432-0827
    Schlagwort(e): Enamel ; Mineralization ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The potassium pyroantimonate technique was used to study the cellular distribution of calcium during the early mineralization of enamel in rat molar tooth germs at the electron microscope level. Differing patterns of calcium distribution were observed in the ameloblast seemingly associated with the appearance of Tomes' process. In the early secretory ameloblast calcium pyroantimonate deposits were observed within the Golgi apparatus, within coated vesicles, within mitochondria and associated with the inner aspect of the cell membrane. However, with the development of Tomes' process the ameloblasts no longer demonstrated these discrete deposits of calcium pyroantimonate. Instead they showed a diffuse cytoplasmic staining pattern with no preference for any particular organelle.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 62
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 27 (1979), S. 13-18 
    ISSN: 1432-0827
    Schlagwort(e): Anticonvulsants ; Calcium ; Vitamin D ; Parathyroid hormone ; Bone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Parameters of mineral metabolism were examined in 6 patients with moderately severe anticonvulsant drug-induced osteomalacia. Compared to 15 matched controls, the patients exhibited significantly reduced serum calcium, inorganic phosphate, and 25-hydroxyvitamin D concentration, elevated serum alkaline phosphatase and immunoreactive parathyroid hormone (iPTH) concentration, reduced intestinal47Ca absorption, reduced urinary calcium and increased urinary hydroxyproline excretion, and reduced forearm bone mass. Intestinal absorption of vitamin D3 was normal. Following 4 months of treatment with vitamin D3 (4000 units/day), serum 25-OHD concentration was increased to 3 times mean normal values and all parameters except serum iPTH, urinary calcium excretion, and forearm bone mass were returned to levels not significantly different from normal. Serum iPTH concentration was reduced by 39% (P〈0.05); 24-h urinary calcium excretion rose by 98% (P〈0.001), and forearm bone mass increased by 5.6% (P〈0.05). It is concluded that moderate-dose vitamin D3 supplementation is effective in normalizing parameters of mineral metabolism in this disorder, despite evidence of resistance to the biologic effects of vitamin D.
    Materialart: Digitale Medien
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  • 63
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 32 (1980), S. 229-236 
    ISSN: 1432-0827
    Schlagwort(e): Bone ; Ion influxes ; Calcium ; Phosphate ; Exchange
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Quantitative measurements were made of the ion fluxes of calcium and phosphate into and from calvaria (mouse or rat) when clamped in specially designed micro-Ussing chambers. The effects of varying concentrations of calcium were examined on the influx and efflux of calcium and of its counterion, phosphate. A comparable series of experiments was performed with varying phosphate concentrations. Both ions, as their concentrations increased, depressed their own influx, increased their own efflux, and significantly increased the equilibrium concentration, E/K, supported by the calvaria. Similarly, both ions, as their concentrations increased, affected the influx or efflux of their counterion only slightly but did depress the counterion's equilibrium level, E/K, significantly. In spite of these changes it was shown that calvaria effectively buffered the medium at physiological concentrations of calcium and phosphate. The buffering capacity, however, was small, and the balance, E/K, was modified by small uptake or loss of either ion. The small size of the interacting mineral pool was confirmed by direct measurement of the rapidly exchanging fractions of both calcium or phosphate. They were only ∼1% of the total ions present. The significance of these findings is discussed.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 34 (1982), S. 43-48 
    ISSN: 1432-0827
    Schlagwort(e): Calcium ; Phosphate ; Phosphatidylserine ; Transport ; Mineralization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Experiments were performed to study the effect of inorganic phosphate (Pi) on phosphatidylserine-mediated Ca2+ transport utilizing two- and three-compartment lipid-aqueous phase model systems. When the three-compartment model was used, the rate of Ca2+ transport from an aqueous donor compartment to an aqueous receiver compartment, separated by a nonaqueous phospholipid phase, was determined. This experiment showed that the rate of Ca2+ transport was proportional to the phosphatidylserine concentration and the pH. Pi modulated the rate of Ca2+ transport; even when the Pi concentration of the donor aqueous phase was low, there was a marked enhancement of transport. To determine whether the Pi-mediated rise in the Ca2+ transport rate was due to an increase in the uptake of Ca2+ into the lipid phase, or to an increase in the ability of the lipid phase to release Ca2+, a two-compartment model was used. It was found that the ability of the phosphatidylserine phase to take up Ca2+ increased as the Pi concentration of the aqueous donor phase was raised. With the increase in Ca2+ uptake there was a concomitant elevation in the rate of Ca2+ transport into an aqueous receiver phase. However, Pi did not stimulate Ca2+ release from the phosphatide. Thus it was concluded that Pi enhanced the interaction between Ca2+ and phosphatidylserine, possibly by forming a Ca-phospholipid-Pi complex. Once this interaction had taken place, Ca2+ release into the aqueous receiver compartment was independent of the Pi concentration.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 139-144 
    ISSN: 1432-0827
    Schlagwort(e): 1,25(OH)2-vitamin D ; Weight loss ; Phosphate ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary During a review of 42 metabolic studies in healthy women and men we observed that serum 1,25-(OH)2-D concentrations were directly correlated to the observed daily changes in body weight (r=0.68;P〈0.001) and to caloric intake/kg/day (r=0.39;P=0.01). These relationships could not be accounted for by related and physiologically expected changes in serum Ca or iPTH concentrations. However, serum 1,25-(OH)2-D concentrations were observed to be inversely correlated to serum PO4 levels (r=−0.44;P=0.004). In addition, serum PO4 levels were inversely correlated to the daily changes in body weight (r=−0.40;P=0.009). Since dietary sodium intake averaged 142 mmol/day, it is unlikely that the observed changes in weight were the result of changes in salt and water balance. Thus it seems reasonable to speculate that serum 1,25-(OH)2-D concentrations may vary directly with energy balance, as reflected by changes in body weight. This effect may be mediated by alterations in PO4 metabolism. The accurate assessment of serum 1,25-(OH)2-D levels thus appears to require several measurements over time periods during which body weight is stable.
    Materialart: Digitale Medien
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  • 66
    ISSN: 1432-0827
    Schlagwort(e): Electromagnetic field ; Bicarbonate ; Phosphate ; Calcium ; Fluoride ; Osteogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The present studies are aimed at establishing molecular correlations in the interaction of very low frequency electromagnetic fields with biological systems. Ca-uptake by chick embryo tibia rudiment in short-term culture was a useful model. Tibiae of 8- to 10-day-old chick embryos were incubated 60 min in simplified culture media in the presence of45Ca at 37.5±0.5°C either inside or outside pulsating electromagnetic fields. Radioactivity count in the medium was the most accurate method for determining Ca-uptake by the rudiment. The effect of the fields on the Ca-uptake depended markedly on the chemical composition of the culture medium: bicarbonate was indispensable; glucose or sucrose was important; phosphate was potentiating; ethanol, Mg2+, and NaF were stimulating. The field had no effect in (a) blank medium without tibia, (b) tibiae that had been altered by fixation with aqueous glutaraldehyde, (c) nonliving artificial systems endowed with great or small ion sorption capacity. The unique bicarbonate effect with living systems and the passive behavior of nonliving ion sorbing systems prompt the suggestion that the electromagnetic field probably couples with specific processes, such as a bicarbonate-dependent Ca2+ ATPase and the active ion transport, at the cell membrane level. The molecular mechanisms remain to be established.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 194-199 
    ISSN: 1432-0827
    Schlagwort(e): Benzo(B)Thiophene-2-Carboxylic Acid ; Bone cells ; Calcium ; Cyclic AMP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The purpose of the present study was to investigate the mechanism of action on bone of Benzo(B)Thiophene-2-Carboxylic Acid (BL-5583). BL-5583, at a dose range of 0.01–100 µg/ml, inhibited spontaneous as well as A23187 and PTH-induced bone resorption in tissue culture. This compound also decreased calcium uptake in both osteoclastic and osteoblastic enriched bone cell populations obtained by sequential collagenase digestion of 1–2 day newborn rat calvariae. The decrease occurred after a 5 min. incubation with45Ca and BL-5583. The effective dose range was 0.01–100 µg/ml. No effect on leucine incorporation or lactic acid production by bone cells was observed. BL-5583 also induced a transient decrease in calcium uptake in skin cells isolated from fetal rats by collagenase digestion, suggesting a lack of tissue specificity for this compound. No effect on cyclic AMP in isolated bone cells was observed with the same dose range that produced a calcium effect.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 36 (1984), S. 702-710 
    ISSN: 1432-0827
    Schlagwort(e): Corticosteroids ; Cartilage ; Organ culture ; Calcium ; Matrix vesicles
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary The present study examined the effects of various corticosteroid and noncorticosteroid hormones upon the ultrastructure of chondroprogenitor cells and chondroblasts in an organ-culture system of late fetal condylar cartilage. Corticosteroids, (triamcinolone acetonide, dexamethasone, corticosterone) at concentrations of 10−6–10−8M stimulated markedly a precocious formation of matrix vesicles by chondroblasts. This stimulation was accompanied by a significant accretion of calcium complexes intra- and extracellularly in both the chondroprogenitor cell population and chondroblastsin vitro, as well as in the newly induced matrix vesicles. Nonglucocorticoid steroids (progesterone, estradiol, testosterone, cortexolone) did not evoke similar effects. Progesterone and testosterone, however, seemed to adversely affect the ultrastructure of the cartilage cells, whereas estradiol appeared to have a favorable effect on the morphology of cultured condylar cartilage.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 34 (1982), S. 121-124 
    ISSN: 1432-0827
    Schlagwort(e): Bone ; Calcium ; Metabolism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Summary Bone Gla protein (BGP) was measured in the plasma by radioimmunoassay (RIA) during treatment of 59 patients with bone diseases including Paget's disease (N=9), primary hyperparathyroidism (N=25), chronic renal failure (N=20), and cancer involving bone (N=5). Plasma BGP was increased above normal in all patients. BGP decreased in the patients with Paget's disease following the acute and chronic administration of salmon calcitonin. Plasma BGP was higher in women then in men with primary hyperparathyroidism. Following parathyroidectomy, BGP decreased in both sexes but the decrease was significant in women only. Plasma BGP was increased in patients with renal osteodystrophy and did not change after hemodialysis. In the patients with bone cancer, plasma BGP decreased during treatment of the attendant hypercalcemia with salmon calcitonin. Although plasma BGP and serum alkaline phosphatase (AP) levels were generally correlated in these studies, there were examples of dissociation between the two. The measurement of plasma BGP appears to provide a specific index of bone metabolism that may in some circumstances be more sensitive than serum alkaline phosphatase measurement. However, further studies are necessary to establish the clinical value of plasma BGP measurement by RIA in the management of patients with bone diseases.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 70
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 114 (1977), S. 43-49 
    ISSN: 1432-072X
    Schlagwort(e): Cyanobacteria ; Anabaena ; Hydrogenase ; Hydrogen-uptake ; Nitrogenase ; Nitrogen fixation ; Protection mechanism ; Inhibitors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The blue-green alga Anabaena cylindrica is found to consume molecular hydrogen in a hydrogenase dependent reaction. This hydrogen uptake proceeds in the dark and is strictly dependent on oxygen, thus representing a Knallgas reactions. Its rate is almost as high as that of the endogenous respiration in Anabaena. Studies with inhibitors reveal that hydrogen is utilized via the complete respiratory chain providing additional energy for the alga. CO plus C2H2 completely block the Knallgas reaction which explains the previously reported considerable increase in the total H2 formation representing the difference between the nitrogenase-dependent H2-evolution and the reutilization of the gas catalysed by the hydrogenase in intact Anabaena. H2 is able to support the C2H2-reduction in the dark in a reaction again strictly dependent on oxygen. Moreover, H2 is also consumed in experiments carried out under far red light and in the presence of dichlorophenyl-dimenthyl-urea (DCMU) where the energy for nitrogen fixation is no longer provided by respiration but by cyclic photophosphorylation. Under these conditions, H2 is found to supply electrons for the formation of C2H4 from C2H2 in a reaction no longer dependent on the presence of oxygen. Moreover, in these experiments, the presence of H2 stabilizes the C2H2-reduction activity against the deleterious effect of oxygen. Thus, this communication provides evidence for a triplicate function of the H2-uptake catalysed by hydrogenase in intact Anabaena which is (a) to provide energy by the Knallgas reaction, (b) to supply reducing equivalents for nitrogenase, (c) to protect nitrogenase from damage by oxygen.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 111 (1976), S. 195-196 
    ISSN: 1432-072X
    Schlagwort(e): Mutation ; Blue-green alga ; Anabaenopsis raciborskii ; Gas vacuole ; Nitrogen fixation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract From a bloom forming blue-green alga, Anabaenopsis raciborskii, spontaneous mutants, which had lost the ability to form gas vacuoles have been isolated; the mutant frequency was 4.8×10-3. The filaments of gas vacuole-less mutants settled at the bottom of flasks in liquid culture media unlike the parent alga. The growth and nitrogen fixation were comparatively poor in the mutants.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 118 (1978), S. 177-184 
    ISSN: 1432-072X
    Schlagwort(e): Cyanobacteria ; Knallgas reaction ; Hydrogenase ; Hydrogen utilization ; Nitrogenase ; Nitrogen fixation ; Isolated heterocysts ; Anabaena cylindrica ; Nostoc muscorum ; Anabaena variabilis ; Anacystis nidulans ; Cyanophora paradoxa
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Several blue-green algae were surveyed for the occurrence of the hydrogenase which was assayed by the oxyhydrogen or Knallgas reaction in the intact organisms. In aerobically grown cultures, the reaction was detectable in Anabaena cylindrica, Nostoc muscorum and in two Anabaena variabilis species, whereas virtually no activity was observed in Anacystis nidulans and Cyanophora paradoxa. In these latter two algae, the reaction was, however, found after growth under molecular hydrogen for several days, which drastically increased the activity levels with all the algae tested. In the nitrogen fixing species, the activity of the Knallgas reaction was enhanced when all combined nitrogen was omitted from the media. H2 and hydrogenase could not significantly support the CO2-fixation in photoreduction experiments with all blue-green algae investigated here. Hydrogenase was assayed by the dithionite and methyl viologen dependent evolution of hydrogen and was found to be present with essentially the same specific activity levels in preparations of both heterocysts and vegetative cells from Anabaena cylindrica. Na2S2O4 as well as H2 supported the C2H2-reduction of the isolated heterocysts. The H2-dependent C2H2-reduction did not require the presence of oxygen but was strictly light-dependent where H2 served as an electron donor to photosystem I of these cells. It is concluded that hydrogen can be utilized by two different pathways in blue-green algae.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 121 (1979), S. 141-145 
    ISSN: 1432-072X
    Schlagwort(e): Azospirillum ; Denitrification ; Nitrogen fixation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The interaction between nitrate respiration and nitrogen fixation inAzospirillum lipoferum andA. brasilense was studied. All strains examined were capable of nitrogen fixation (acetylene reduction) under conditions of severe oxygen limitation in the presence of nitrate. A lag phase of about 1 h was observed for both nitrate reduction and nitrogenase activity corresponding to the period of induction of the dissimilatory nitrate reductase. Nitrogenase activity ceased when nitrate was exhausted suggesting that the reduction of nitrate to nitrite, rather than denitrification (the further reduction of nitrite to gas) is coupled to nitrogen fixation. The addition of nitrate to nitrate reductase negative mutants (nr-) ofAzospirillum did not stimulate nitrogenase activity. Under oxygen-limited conditionsA. brasilense andA. lipoferum were also shown to reduce nitrate to ammonia, which accumulated in the medium. Both species, including strains ofA. brasilense which do not possess a dissimilatory nitrite reductase (nir-) were also capable of reducing nitrous oxide to N2.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 123 (1979), S. 37-45 
    ISSN: 1432-072X
    Schlagwort(e): Cyanobacteria ; Blue-green algae ; Hydrogen metabolism ; Nitrogen fixation ; Isolated heterocysts ; Inhibitors ; Plastoquinone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Several natural and artificial electron donors were assayed in the C2H2-reduction of heterocysts isolated from the cyanobacterium Anabaena cylindrica. Among these, molecular hydrogen was the most effective one when the assays were performed in the light. The C2H2-reduction and the Knallgas reaction of intact Anabaena filaments as well as the H2-supported C2H2-reduction of isolated heterocysts were compared for their sensitivity towards several inhibitors known to affect the photosynthetic or respiratory electron flow. Among these, dibromothymoquinone (DBMIB) affected all three reactions equally indicating that plastoquinone is a common intermediate of the H2-consumptions by either the respiratory or the photosynthetic electron transport. Metronidazole inhibited the H2-utilization via photosynthesis but did not affect the consumption of this gas by respiration and therefore allows to differentiate between the two pathways of hydrogen utilization. The studies with the inhibitors are suggestive for a segment of electron carriers on the membranes common to both photosynthesis and respiration in heterocysts of Anabaena.
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 123 (1979), S. 93-99 
    ISSN: 1432-072X
    Schlagwort(e): Movement ; Phototaxis ; Cations ; Chlamydomonas ; Calcium ; Lanthanum ; Circadian rhythms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effects of several cations on phototaxis of Chlamydomonas reinhardtii have been studied with the aid of an automated phototaxis monitoring device, coupled with a continuous culture. Sodium, potassium and magnesium ions, if added to the complete nutrient medium, have only slight effects on phototaxis at lower concentrations (10-3 mol), but inhibit at higher concentrations (10-2 mol). This inhibitory effect is not specific because motility is also impaired. Addition of 10-3 mol calcium enhances the phototactic reaction for some hours, but then the stimulation decreases gradually. Addition of 10-2 mol calcium causes strong inhibition. However, the reactivity recovers gradually during the following hours. If 10-3 mol potassium which does not influence phototaxis if added alone is applied simultaneously with calcium, the stimulation by calcium is enhanced. By the addition of 5·10-4—2·10-3 mol Ca2+ or Ca2++K+ cicadian rhythms with an average period length of 24 h are initiated which damp out after 1–2 weeks. If the cells are grown in a calcium deficient medium or if calcium is removed, phototactic activity decreases to very low reaction values or to zero, but is drastically increased immediately after the addition of calcium. The stimulatory effect of Ca2+ ions is specific. Ca2+ cannot be fully substituted by Ba2+ or Sr2+, and phototaxis is reversibly inhibited by lanthanum which is known to inhibit the calcium pump.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 123 (1979), S. 259-265 
    ISSN: 1432-072X
    Schlagwort(e): Nitrogen fixation ; Nitrogenase ; Gene expression ; Protein synthesis ; Regulation ; Klebsiella pneumoniae ; Microbial ecology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract At growth temperatures above 37°C, Klebsiella pneumoniae does not grow in a medium containing N2 or NO 3 - as nitrogen sources. However, both the growth in the presence of other nitrogen sources as well as the in vitro nitrogenase activity are not affected at this temperature. The inability to fix N2 at high temperature is due to the failure of the cells to synthesize nitrogenase and other nitrogen fixation (nif) gene encoded proteins. When cells grown under nitrogen fixing conditions at 30°C were shifted to 39°C, there was a rapid decrease of the rate of de novo biosynthesis of nitrogenase (component 1), nitrogenase reductase (component 2), and the nifJ gene product. There was no degradation of nitrogenase at the elevated temperature since preformed enzyme remained stable over a period of at least 3 h at 39°C. Thus, temperature seems to represent a third control system, besides NH 4 + and O2, governing the expression of nif genes of K. pneumoniae.
    Materialart: Digitale Medien
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  • 77
    ISSN: 1432-072X
    Schlagwort(e): Fluorescent antibody staining ; Nitrogen fixation ; Symbiosis ; Anabaena azollae ; Azolla caroliniana
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Fluorescent antibody staining indicated differences in surface antigenicity in Anabaena azollae cells fresh from the leaf cavities of the fern, Azolla caroliniana, and algae which were isolated and subcultured from this fern. Such results suggest that either changes in antigenicity occur in this phycobiont during culturing or that isolation selects for an antigenically different mutant strain capable of in vitro growth.
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  • 78
    ISSN: 1432-072X
    Schlagwort(e): Nitrogen fixation ; Regulation ; Guanosine 5′-diphosphate 3′-diphosphate (ppGpp)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Addition of ammonium to N2 fixing cultures of Azotobacter vinelandii, Klebsiella pneumoniae and Clostridium pasteurianum rapidly reduced the intracellular levels of guanosine 5′-diphosphate 3′-diphosphate (ppGpp) by 70–90%. This change might reflect a regulatory role of ppGpp in nitrogen metabolism.
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  • 79
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 132 (1982), S. 219-224 
    ISSN: 1432-072X
    Schlagwort(e): Rhizobium ; Nitrogen fixation ; Nodules ; Soybean
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Several mutants defective in nodulation were isolated from Rhizobium japonicum strains 3I1b110 and 61A 76. Mutants of class I do not form nodules after incubation with soybean [Glycine max (L.) Merrill] for 17 days, but will do so by 28 days. When host plants other than G. max are infected with several of these strains, there is no detectable difference in the time of nodulation or size of nodules as compared to the wild type. Two mutants of class I (i. e., SM1 and SM2) have been shown previously to be altered in the lipopolysaccharide portion of their cell wall. Mutants of class II are not slow to nodulate but form fewer nodules than the wild type on all the host plants tested. Mutants of class III are unable to form nodules. Some bacteriophage-resistant mutants, altered in cell surface structure, fall into this class. Two mutants of class III do not bind to soybean roots.
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  • 80
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 132 (1982), S. 333-337 
    ISSN: 1432-072X
    Schlagwort(e): Anabaena variabilis Kütz ; 14C-prelabeled blue-green algae ; Interaction respiration/photosynthesis ; CO2 exchange ; Nitrogen fixation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Prelabeled Anabaena variabilis Kütz. evolves 14CO2 in the light with KCN and DCMU (2,4-dichlorophenyl-1,1-dimethylurea) present, comparable to the dark control without inhibitors added. Double-reciprocal plots of CO2 release vs. light intensity with either KCN or KCN+DCMU present result in two straight lines intersecting at the ordinate. Apparently, reducing equivalents originating from carbohydrate catabolism are channeled into the photosynthetic electron-transport chain, competing for electrons from photosystem II. Under these conditions, the CO2 release is accompanied by a light-dependent oxygen uptake, presumably due to oxygen-reducing photosystem-I activity while ribulose-bisphosphate carboxylase is inhibited by KCN. Comparing nine blue-green algae it was shown that only nitrogen-fixing species release substantial amounts of CO2 in the light with KCN or KCN+DCMU present. This release is particularly obvious with Anabaena variabilis Kütz. under nitrogen-fixing conditions, but small when the alga is grown with combined nitrogen. We conclude that nitrogen-fixing species share a common link between respiratory and photosynthetic electron transport. The physiological role may be electron supply of nitrogenase by photosystem I.
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  • 81
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 130 (1981), S. 38-43 
    ISSN: 1432-072X
    Schlagwort(e): Nitrogen fixation ; Gene expression ; Regulation ; Messenger RNA ; Transcription ; Klebsiella pneumoniae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nitrogenase messenger RNA synthesis in Klebsiella pneumoniae was determined by labelling cells with (3H)uracil and isolating total RnA, which was then hybridized to filterbound recombinant plasmid pSA30 DNA carrying the nitrogenase structural genes nifH, D, and K. Derepression of nitrogenase mRNA starts 1.5 h before the onset of nitrogenase activity (as measured by acetylene reduction). Exposure of nif-derepressed cultures to either NH 4 + , air, or high temperatures (39° C) results in a rapid decrease of the synthesis rates both of nitrogenase mRNA and nitrogenase polypeptides. Nitrogenase mRNA is remarkably stable. After blocking transcription with rifampicin, hybridizable and actively translatable nitrogenase mRNA survives with an average half-life of 18 min. Half-lives are considerably shorter when rifampicin-inhibited cultures are simultaneously shifted to conditions which are non-permissive for nitrogenase synthesis, pointing to some posttranscriptional influence on nitrogenase mRNA stability. In all experiments performed there was no evidence for uncoupling of nitrogenase mRNA synthesis from nitrogenase mRNA translation, indicating that nitrogenase synthesis is regulated solely by transcriptional control.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    Springer
    Environmental management 7 (1983), S. 177-187 
    ISSN: 1432-1009
    Schlagwort(e): Nitrogen ; Model ; Agriculture ; Mass balance ; Ground-water ; Denitrification ; Immobilization ; Dry deposition ; Nitrogen fixation ; Nitrate ; Florida
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract A detailed nitrogen budget was devised for agricultural activities in the Florida peninsula, based on routine data published by state agricultural agencies. The model demonstrates that important unmonitored fluxes of nitrogen can often be calculated by mass balance on individual model compartments, and that the reasonability of poorly quantified fluxes can be assessed. The results of such models can be very useful in designing and assessing the results of field experiments and in prioritizing environmental monitoring programs.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 3 (1977), S. 55-58 
    ISSN: 1432-1017
    Schlagwort(e): Rhodopsin ; Rods ; Phototransduction ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract Difficulties in testing the possible role of calcium as a Transmitter in the R.O.S. are discussed. A comparison is made with the Sarcoplasmic Reticulum system where calcium flux are easily measured. The latest results reviewed on intact cellular structures are highly indicative but not yet conclusive.
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 3 (1977), S. 141-143 
    ISSN: 1432-1017
    Schlagwort(e): Calcium ; Limulus ; Photoreceptors ; Adaptation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract Calcium ion fulfills several criteria for identifying an intracellular messenger for light-adaptation in Limulus photoreceptors. Direct injection of Ca++ mimicks two aspects of light-adaptation; sequestration of intracellular calcium tends to prevent light-adaptation; and light induces an increase in intracellular Ca++ as demonstrated by two independent techniques.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 85
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 3 (1977), S. 145-151 
    ISSN: 1432-1017
    Schlagwort(e): Visual cell membranes ; Invertebrates ; Ion channels ; Activation of light channels ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract It is assumed that “dark channels” determine a permanent dark conductance of the arthropod visual cell membrane. The light stimulus causes a transient opening of “light channels”. The ion selectivity of dark channels and light channels is roughly described. Factors influencing the activation of light channels, as membrane energy metabolism, membrane potential and adjusted calcium ion concentration are specified. The mechanism of the action of calcium ions on the conductance of the visual cell membrane is discussed.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 5 (1979), S. 33-41 
    ISSN: 1432-1017
    Schlagwort(e): Rhodopsin ; Calcium ; Reaction kinetics ; Regeneration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract The formation of metarhodopsin II in various bovine rhodopsin preparations (rod outer segment (ROS) suspensions and rhodopsin-detergent solutions) was measured by means of flash spectrophotometry. The half-lifetime and formation of metarhodopsin II in ROS did not depend on the calcium concentration in the range of less than 10−9 M (using EGTA or EDTA) to 15×10−3 M calcium at pH values of 5.0, 7.1, and 9.0 (Table 1). The regeneration of rhodopsin from opsin by adding 11-cis retinal to ROS-suspensions and rhodopsin digitonin solutions was measured spectrophotometrically. It was not substantially different in either saline, one containing less than 10−7 M calcium (by adding EGTA), the other containing 10−3 M calcium (Table 2).
    Materialart: Digitale Medien
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  • 87
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 5 (1979), S. 223-230 
    ISSN: 1432-1017
    Schlagwort(e): Prolonged depolarising after-potential (PDA) ; Visual pigment ; Invertebrate photoreceptor ; Manganese ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract We have studied the effects on the PDA of modifying intracellular and extracellular concentrations of Ca2+ and Mn2+. The effect of decreased Ca2+ concentration or addition of EGTA is mainly an increase in the PDA amplitude and length. Raising Ca2+ concentration using ruthenium red or high external Ca2+ has the opposite effect. The effect of Mn2+ is much more striking: In the presence of 50–100 mM Mn2+ the PDA is initially greatly depressed but can rise slowly for up to 20 or 30 s (in the dark) until it approaches its original amplitude and time course. Bridge measurements showed that the depression of the PDA corresponds to a depressed conductance and so is not due to an increase in K+ conductance. The Mn2+ effect is potentiated by decreased Ca2+. Appropriate stimulation suppresses the rising PDA as promptly as it does a normal PDA, suggesting that if lateral diffusion is the source of the slow rise, the PDA and PDA-depressing processes must be spatially linked. The action of the anti-PDA is apparently prolonged by both Ca2+ and Mn2+.
    Materialart: Digitale Medien
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  • 88
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 9 (1982), S. 131-136 
    ISSN: 1432-1017
    Schlagwort(e): Chemotaxis ; Calcium ; Oscillation ; Dictyostelium ; Ionophore
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract Migration of differentiated cells to a capillary containing cyclic AMP was enhanced in the presence of 1 mM CaCl2 and was virtually absent in the presence of 1 mM EGTA. Furthermore, the cells contracted and extended pseudopods to a capillary filled with the calcium ionophore A 23187. At short distances, migration to the tip of the capillary was observed. The ionophore also induced transient decreases of the optical density of suspended cells indicating changes of cell shape. These findings support the hypothesis that cyclic AMP-binding to cell surface receptors causes a local influx of calcium ions. These in turn lead to an increase of the cytosolic calcium concentration and subsequently to an activation of cell migration. Perturbing pulses of the ionophore induced permanent phase shifts of free-running light scattering oscillations. This result indicates that cytosolic calcium is an intrinsic component of the oscillatory system.
    Materialart: Digitale Medien
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  • 89
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 107 (1976), S. 25-31 
    ISSN: 1432-072X
    Schlagwort(e): Ferredoxin ; Iron-sulfur proteins ; Nitrogen fixation ; Electron transport to nitrogenase ; Flavodoxin ; Mycobacterium flavum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract 1. Two ferredoxin-type iron-sulfur proteins have been isolated from Mycobacterium flavum 301 grown under nitrogen-fixing, iron-sufficient conditions. No flavodoxin was observed. 2. These ferredoxins are apparently soluble: they were present in the supernatant fraction after disrupting by decompression. Only small amounts were present in particulate fractions. 3. The two ferredoxins were separated by chromatography on DEAE-cellulose, Sephadex or electrophoresis. 4. Both ferredoxins mediated the transfer of electrons from illuminated spinach chloroplasts to a nitrogenase preparation to reduce acetylene. Ferredoxin II was specifically about five times more active than ferredoxin I. Ferredoxin II was also active in the photosynthetic NADP+-reduction whereas ferredoxin I was not. 5. Both ferredoxins were reversibly reduced by either sodium dithionite, illuminated spinach chloroplasts or hydrogen plus hydrogenase from Clostridium pasteurianum. 6. Attempts to determine the primary electron donor for nitrogen fixation in Mycobacterium flavum were unsuccessful. Acetylene reduction in Mycobacterium extracts was obtained only with sodium dithionite or illuminated spinach chloroplasts as electron donors. The reduction of the electron carrier (e. g. ferredoxin) rather than the transfer of electrons from the reduced carrier to nitrogenase was rate-limiting.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 90
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 107 (1976), S. 235-240 
    ISSN: 1432-072X
    Schlagwort(e): Hydrogen bacteria ; Nitrogen fixation ; Acetylene reduction ; Mycobacterium flavum 301 ; Corynebacterium autotrophicum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Seventeen strains of nitrogen-fixing bacteria, isolated from different habitats on hydrogen and carbon dioxide as well as on other substrates, morphologically resembled each other. All strains, including Mycobacterium flavum 301, grew autotrophically with hydrogen. The isolate strain 6 was sensitive to oxygen when dependent on N2 as nitrogen source, a consequence of the sensitivity of its nitrogenase towards oxygen. At the same time, strain 6 was sensitive to hydrogen when growing autotrophically on N2 as nitrogen source, but hydrogen did not affect acetylene reduction by these cells.
    Materialart: Digitale Medien
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  • 91
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 107 (1976), S. 263-267 
    ISSN: 1432-072X
    Schlagwort(e): Nitrogen fixation ; Root nodule ; Endophyte vesicle ; Alder ; Alnus ; Freeze-etching
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nitrogen-fixing root nodules of Alnus crispa var. mollis Fern. were studied by transmission electron microscopy and by freeze-etching technique. Ultrathin sectioning of septate vesicles of the actinomycetal endophyte showed an electron transparent zone, the so-called “void area”, between the vesicle cell wall and its encapsulation material. This void area was not observed in the freeze-etching replicas of cryoprotected nodular tissue. It is suggested that the void area is the result of the coming-off of the vesicle cell wall from the capsule and that its formation reflects difficulty in fixing the voluminous mature vesicle of the root nodule endophyte.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 114 (1977), S. 197-201 
    ISSN: 1432-072X
    Schlagwort(e): Anabaena sp. ; Nitrogen fixation ; Heterocysts ; Cyanobacteria ; Marine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A marine filamentous cyanobacterium capable of rapid growth under N2-fixing conditions has been isolated from the Texas Gulf Coast. This organism appears to be an Anabaena sp. and has been given the strain designation CA. Cultures grown on mineral salts medium bubbled with 1% CO2-enriched air at 42°C show a growth rate of 5.6±0.1 generations per day with molecular nitrogen as the sole nitrogen source. This growth rate is higher than any other reported in the literature to date for heterocystous cyanobacteria growing on N2. Under similar growth conditions, 7.5 mM NH4Cl yields a growth rate of 6.6±0.1 generations per day while 7.5 mM KNO3 allows for a growth rate of 5.8±0.4 generations-day. Nitrogen-fixation rates, as measured by acetylene reduction, show maximum activity values in the range of 50–100 nmoles ethylene produced/minxmg protein. These values compare favorably with those obtained from heterotrophic bacteria and are much higher than values reported for other cyanobacteria. Growth experiments indicate that the organism requires relatively high levels of sodium and grows maximally at 42°C. Because of its high growth rate on N2, this newly isolated organism appears ideal for studying nitrogen metabolism and heterocyst development among the cyanobacteria.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 120 (1979), S. 161-165 
    ISSN: 1432-072X
    Schlagwort(e): Azolla ; Cyanobacteria ; Blue-green algae ; Nitrogen fixation ; Symbiont ; Photoheterotroph ; Algal isolation ; Photosynthesis ; Plant metabolism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A procedure has been developed to isolate cyanobacteria from the aquatic fern Azolla. The method is based upon recovery of cyanobacterial “bundles” from digests of plants and use of this material as a massive inoculum for nitrogen-free media, followed by prolonged incubation in light. The procedure appears to select for those cells capable of growth in vitro. Isolated cyanobacteria were found to resemble Anabaena sp. morphologically but were capable of heterotrophic growth and had high nitrogenase activity when grown on fructose in the dark.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 122 (1979), S. 153-159 
    ISSN: 1432-072X
    Schlagwort(e): Rhizobium japonicum ; Nitrogenase activity ; Nitrogen fixation ; Organic acids ; Cell-morphology ; Bacteroids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Rhizobium japonicum 61-A-101 grew and fixed nitrogen more effectively on media containing an organic acid and a pentose sugar than on media containing only one of these carbon sources. Peak specific activities in the range 10–15 nmol C2H4 · h-1 · mg protein-1 were found for these organisms in a spot of growth about 1 cm diameter on agar surfaces exposed to air. Increasing concentrations of the organic acids (succinate or malonate) in a medium containing arabinose resulted in longer lasting activity. The inclusion of a third carbon source, glycerol, gave activity which remained at the maximum from about the 8 to the 18 day after inoculation although no growth of the bacteria occurs during the last 8 or 10 days. At low concentration of organic acid l-arabinose was a much better carbon source for supporting nitrogenase activity of these organisms that the d-form. Both organic acids affected the morphology of the bacteria. Higher concentrations, especially of malonate, gave swollen and distorted cells. When bacteria growing on organic acid-containing agar plates were suspended and plated after appropriate dilution on yeast extract — mannitolglycerol agar there was heterogeneity of colony form, with up to 90% microcolonies after growth on high malonate concentrations. The effects of malonate may be correlated with characteristics of the bacteroid form inside the nodule which contains relatively high concentrations of organic acids, especially malonate.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 116 (1978), S. 113-118 
    ISSN: 1432-072X
    Schlagwort(e): Hydrogen evolution ; Hydrogenase ; Nodules ; Bacteroids ; Nitrogenase ; Rhizobium leguminosarum ; Acetylene reduction ; Nitrogen fixation ; Pisum sativum ; Legumes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Hydrogen evolution from root nodules has been reported to make N2 fixation by some legume-Rhizobium symbiotic systems inefficient. We have surveyed the extent of H2 evolution and estimated relative efficiencies of nodules of Austrian winter peas formed by 15 strains of R. leguminosarum. Their rates of H2 evolution in air were about 30% of the rates of H2 evolution under an atmosphere in which N2 was replaced by Ar. Relative efficiency values based on C2H2 reduction rates ranged from 0.55 to 0.80. With some of the strains, hydrogenase activities were demonstrated in intact nodules and in bacteroids, but the levels of activity were insufficient to recycle all the H2 evolved by the nitrogenase system. In both intact nodules and bacteroids the hydrogenase is less sensitive to O2 damage than the nitrogenase system, so H2 uptake capacity was observed in intact nodules by suppressing the nitrogenase-dependent H2 evolution with an atmosphere containing a high O2 concentration, and in bacteroids by using aerobically prepared bacteroid suspensions. The hydrogenase activity of both was dependent on O2 consumption. A K mfor H2 of near 4 μM was determined in suspension of bacteroids from nodules formed by strains 128C53 and 128C56.
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 123 (1979), S. 227-232 
    ISSN: 1432-072X
    Schlagwort(e): Hydrogen production ; Nitrogen fixation ; Photosynthesis ; Cyanobacteria ; Enrichment cultures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Seventy-one cyanobacteria containing cultures were enriched from various soil and water locations either under aerobic and/or anaerobic conditions on agar medium selective for nitrogen fixation. Kept under argon containing 1% CO2 for 24 and 48 h most of these cultures evolved hydrogen at very variable rates up to 116 μl per mg chlorophyll and hour as a mean value over a time period of 24h. Several samples evolved hydrogen more efficiently compared with known hydrogen producing pure strains from culture collections. Thirty-one of the investigated cultures showed a hydrogen formation higher than 10 μl per mg chlorophyll and hour measured over 24 or 48 h. Among these all the morphological forms of cyanobacteria i.e. unicellular and filamentous with or without heterocysts are found. Hence, selecting for nitrogen fixing cyanobacteria seems to be a practical method to find efficient hydrogen producers.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 127 (1980), S. 163-165 
    ISSN: 1432-072X
    Schlagwort(e): Nitrogen fixation ; Arthrobacter ; Corynebacterium ; Anabaena azollae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Coryneform bacteria were found associated with the nitrogen fixing blue-green alga, Anabaena azollae in the leaf cavity of Azolla caroliniana. Plate counts indicated ca. 7,400±1,900 bacterial cells per mature leaf cavity or approximately 1 bacterial cell for every algal cell. No other type of bacterium was found in these cavities.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 127 (1980), S. 115-118 
    ISSN: 1432-072X
    Schlagwort(e): Proteus mirabilis ; Serratia marcescens ; Erwinia herbicola ; Nitrogen fixation ; nif genes ; his genes ; Plasmids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Plasmid pRD1, an R plasmid of the P incompatibility group which carries his and nif genes from Klebsiella pneumoniae in addition to drug resistance markers derived from RP4, was transferred to His- mutants of Serratia marcescens, Erwinia herbicola and Proteus mirabilis. His+ transconjugants were obtained at low but different frequencies according to recipient genus. Transconjugants all acquired the drug resistance, and were Nif+ in S. marcescens and E. herbicola, having acetylene-reducing activities of the same order of magnitude as the parent K. pneumoniae and fixing 15N2. No evidence for nif expression in P. mirabilis transconjugants was obtained though the nif genes were present.
    Materialart: Digitale Medien
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 133 (1982), S. 6-10 
    ISSN: 1432-072X
    Schlagwort(e): Rhodospirillaceae ; Rhodopseudomonas globiformis ; Nitrogen metabolism ; Nitrogen fixation ; Glutamine synthetase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Rhodopseudomonas globiformis strain 7950 grew with a variety of amino acids, urea, or N2 as sole nitrogen sources. Cultures grown on N2 reduced acetylene to ethylene; this activity was absent from cells grown on nonlimiting NH 4 + . Glutamate dehydrogenase could not be detected in extracts of cells of strain 7950, although low levels of an alanine dehydrogenase were present. Growth ofR. globiformis on NH 4 + was severely inhibited by the glutamate analogue and glutamine synthetase inhibitor, methionine sulfoximine. High levels of glutamine synthetase (as measured in the γ-glutamyl transferase assay) were observed in cell extracts of strain 7950 regardless of the nitrogen source, although N2 and amino acid grown cells contained somewhat higher glutamine synthetase contents than cells grown on excess NH 4 + . Levels of glutamate synthase inR. globiformis were consistent with that reported from other phototrophic bacteria. Both glutamate synthase and alanine dehydrogenase were linked to NADH as coenzyme. We conclude thatR. globiformis is capable of fixing N2, and assimilates NH 4 + primarily via the glutamine synthetase/glutamate synthase pathway.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 133 (1982), S. 312-317 
    ISSN: 1432-072X
    Schlagwort(e): Rhizobium japonicum ; Rhizobium leguminosarum ; Formate metabolism ; Formate dehydrogenase ; Nitrogen fixation ; Nitrogenase ; Bacteroids ; Symbiosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Formate metabolism supported nitrogen-fixation activity in free-living cultures of Rhizobium japonicum. However, formate0dependent nitrogense activity was observed only in the presence of carbon sources such as glutamate, ribose or aspartate which by themselves were unable to support nitrogenase activity. Formate-dependent nitrogenase activity was not detected in the presence of carbon sources such as malate, gluconate or glycerol which by themselves supported nitrogenase activity. A mutant strain of R. japonicum was isolated that was unable to utilise formate and was shown to lack formate dehydrogenase activity. This mutant strain exhibited no formate-dependent nitrogenase activity. Both the wild-type and mutant strains nodulated soybean plants effectively and there were no significant differences in the plant dry weight or total nitrogen content of the respective plants. Furthermore pea bacteroids lacked formate dehydrogenase activity and exogenously added formate had no stimulatory effect on the endogenous oxygen uptake rate. The role of formate metabolism in symbiotic nitrogen fixation is discussed.
    Materialart: Digitale Medien
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