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  • Hydroxyapatite  (5)
  • Fire intensity  (3)
  • Induction  (3)
  • Springer  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of hydroxyapatite dissolution in acetic, lactic, and phosphoric acid solutions (1992)
    Springer
    Calcified tissue international 50 (1992), S. 137-143 
    Details
    ISSN: 1432-0827
    Keywords: Hydroxyapatite ; Enamel ; Dissolution ; Kinetics ; Caries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The present study was undertaken in an attempt to relate the kinetics of hydroxyapatite dissolution to solution parameters, under experimental conditions relevant to the dental caries process. Thus, the dissolution of hydroxyapatite was studied in acetic, lactic, and dilute phosphoric acid solutions having initial pH values from 4 to 6. Rates of dissolution and the corresponding degree of saturation with respect to hydroxyapatite were determined at various times throughout the dissolution process. Rates of dissolution of all solutions were found to decrease with increasing degree of solution saturation and were greater in solutions with lower initial values of pH. However, rates of dissolution in partially saturated phosphoric acid solutions (without added organic acid) were at least one order of magnitude lower than those observed in the organic acid buffers with the same initial pH, over the same range of saturation values. The data obtained are consistent with a surface-controlled dissolution model in which the rate of dissolution is dependent upon the degree of saturation and the sum of the activities of the acidic species in solution, i.e., phosphoric and organic acids. These results suggest that in order to assess the cariogenic potential of a given medium (e.g., plaque fluid), one must determine both the degree of saturation with respect to the dissolving mineral and the activities of acidic species in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298791
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  • 2
    Electronic Resource
    Electronic Resource
    Precipitation of hydroxyapatite from dilute solutions upon seeding (1977)
    Springer
    Calcified tissue international 24 (1977), S. 47-57 
    Details
    ISSN: 1432-0827
    Keywords: Calcification ; Crystal growth ; Hydroxyapatite ; Kinetics ; Precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The kinetics of precipitation of hydroxyapatite, HA, was studied by seeding dilute supersaturated solutions with well characterized HA crystals. In solutions having initial degrees of supersaturation comparable to those present in human serum, the precipitation rates were related to the thermodynamic driving force (degree of supersaturation with respect to HA) and not to the solution composition. The following relationshipR 0=KA(DS) n , whereR 0=initial precipitation rate, A=amount of seeds, DS=degree of supersaturation, and K andn are parameters obtained from the experimental data, was found to apply over a DS range of 6.6×1010 to 3.3×106. These observations are consistent with the occurrence of a simple growth process on the HA seeds. No evidence for the formation of discrete calcium phosphates other than HA was detected. The Ca/P molar ratio of the precipitating phase, calculated from solution compositions, was invariably higher than that expected for HA; this result is shown to be consistent with an initial adsorption phenomenon. Anomalous kinetic behavior was observed at low seeding levels and may relate to the surface phenomenon described. It is concluded that, most probably, under physiological conditions, formation and remineralization of hard tissues occur through the reported crystal growth process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02223296
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of human salivary proteins on the precipitation kinetics of calcium phosphate (1979)
    Springer
    Calcified tissue international 28 (1979), S. 7-16 
    Details
    ISSN: 1432-0827
    Keywords: Salivary proteins ; Adsorption ; Hydroxyapatite ; Precipitation inhibitors ; Crystal growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Inhibition of calcium phosphate precipitation in saliva, and prevention of the formation of mineral accretions on tooth surfaces, has been ascribed to the existence of inhibiting salivary macromolecules. Marked reductions in the crystal growth rate of hydroxyapatite (HA) seeds were measured in supersaturated solutions containing either of two proline-rich proteins, PRP1 or PRP3, or statherin; the three macromolecules were isolated from human parotid saliva. The reductions were also observed when the HA seeds were pretreated with solutions of the macromolecules before adding them to the supersaturated calcium phosphate solution. This effect was very similar in the case of the two PRPs and it was directly related to the extent of adsorption site coverage of these proteins on the HA seeds. The effect of statherin was larger than anticipated from its adsorption behavior. However, comparison on the basis of number of moles adsorbed per unit area of HA shows that the PRP are more effective inhibitors than statherin. The macromolecule concentrations used were considerably lower than those in the salivery secretions, therefore these macromolecules could readily prevent mineral accretion on tooth surfaces through their adsorption onto the enamel surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441212
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  • 4
    Electronic Resource
    Electronic Resource
    Inhibition of apatite crystal growth by the amino-terminal segment of human salivary acidic proline-rich proteins (1984)
    Springer
    Calcified tissue international 36 (1984), S. 651-658 
    Details
    ISSN: 1432-0827
    Keywords: Salivary proteins ; Hydroxyapatite ; Adsorption ; Precipitation-inhibitor ; Phosphoserine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Inhibition of seeded apatitic crystal growth by human salivary acidic proline-rich phosphoproteins (PRP) has been related to their adsorption onto the apatite seeds. The amino-terminal 30-residue segment of the PRP makes an important contribution to this adsorption. This peptide (PRP1(T1)) and its dephosphorylated analogue from PRP3 (PRP3(T1)DP) were prepared. They have identical sequences, except the phosphates at residues 8 and 22 in PRP1(T1) are absent from PRP3(T1)DP. Adsorption of these peptides onto hydroxyapatite and their effect on crystal growth from a defined supersaturated solution was studied. Adsorption behavior was adequately described by the Langmuir adsorption isotherm. The adsorption affinity constant of PRP1(T1) (K=20,200 ml/µmol) was more than 10 times the corresponding value for PRP3(T1)DP (1,800 ml/µmol), and similar to that of the parent protein, PRP1 (26,200 ml/µmol). Inhibition of crystal growth by the peptides was interpreted in terms of the fractional coverage of the maximum number of adsorption sites (as derived from the adsorption isotherms), suggesting that the molecules block, by adsorption, specific growth sites on these surfaces. Comparison of precipitation kinetics showed that PRP1(T1) is a more effective inhibitor than PRP3(T1)DP at the same initial concentration (10−6−10−7 M). However, on the basis of per mol adsorbed, PRP3(T1)DP displays a greater inhibitory activity; such a behavior is consistent with a more open molecular structure which blocks more growth sites per mol adsorbed than PRP1(T1). Because of its high affinity constant, preadsorbed PRP1(T1) remains in the condensed state in the supersaturated solution used, whereas the preadsorbed PRP3(T1)DP molecules desorb to some extent, resulting in a decrease in inhibitory activity. The results show that the amino-terminal segment of the PRP and the two phosphoserine residues present in this segment are particularly important in the function proposed for these proteins in the oral environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405385
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  • 5
    Electronic Resource
    Electronic Resource
    Adsorption of molecules of biological interest onto hydroxyapatite (1984)
    Springer
    Calcified tissue international 36 (1984), S. 48-59 
    Details
    ISSN: 1432-0827
    Keywords: Salivary proteins ; Adsorption ; Thermodynamics ; Kinetics ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Equilibrium and kinetic experiments were conducted to investigate the factors determining the adsorption of salivary macromolecules onto hydroxyapatite. Using amino acids and other small adsorbates, it was determined that the carboxyl attached to the α carbon does not appear to adsorb onto HA and the affinities of side-chain carboxyls are much smaller than that of the phosphate group (phosphoserine). Hydroxyl (serine) displays an extremely high affinity, but its adsorption site on HA is different and the number of such sites is much smaller than found for the rest of the functional groups investigated. It is shown that the information obtained from small molecules cannot be readily applied to prediction of the adsorption behavior of salivary macromolecules and polypeptides. The kinetics of adsorption of the salivary phosphopeptide statherin, a polyaspartate, and the salivary prolinerich phosphoprotein PRP3 are consistent with the reversibility of the adsorption process; no conclusion was possible in the case of the protein PRP1. Apparent irreversibility cannot be explained on the basis of multipoint binding or the properties of the carboxyl versus phosphate group; it appears that secondary structure determines to a significant extent the adsorption properties of the macromolecules. Calculation of the thermodynamic molar quantities of adsorption of PRP1, PRP3, andl-ASP onto HA showed that the process is entropically driven. The functional relationship between partial molar entropy and adsorption coverage is similar for the two proteins, but quite different from that for aspartate. Explanations for these results are advanced on the bases of changes in structure configurations and displacement of water from the adsorbate and the adsorbent surface, the second factor being the dominant one in the adsorption of a small molecule such asl-ASP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405293
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  • 6
    Electronic Resource
    Electronic Resource
    Demography of Adenostoma fasciculatum after fires of different intensities in southern California chaparral (1993)
    Springer
    Oecologia 96 (1993), S. 95-101 
    Details
    ISSN: 1432-1939
    Keywords: Fire intensity ; Adenostoma fasciculatum ; Lignotuber ; Resprouting ; Herbivory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Changes in the population structure of the lignotuberous resprouter Adenostoma fasciculatum were investigated by experimentally burning at various intensities an old stand in southern California chaparral. Survival after fire, time of resprouting, herbivory, and survival after resprouting were monitored for more than 1 year after the fire. Greater fire intensity increased plant mortality and the size of plants that died as a consequence of the fire. Time from the fire until resprouting increased with increasing fire intensity and was related to plant size: the larger the plants the earlier they resprouted. Post-resprouting mortality also increased with fire intensity and was related to time of resprouting. Herbivory increased with fire intensity and the size of plants affected by it changed with the intensity of the fire. Fire intensity had profound direct and indirect effects on the population structure of Adenostoma fasciculatum. Plant size strongly determined the direct and indirect lethal effects of fire.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318035
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  • 7
    Electronic Resource
    Electronic Resource
    Fire intensity and herbivory effects on postfire resprouting of Adenostoma fasciculatum in southern California chaparral (1991)
    Springer
    Oecologia 85 (1991), S. 429-433 
    Details
    ISSN: 1432-1939
    Keywords: Adenostoma fasciculatum ; California chaparral ; Fire intensity ; Herbivory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Resprouting is the main regeneration mechanism after fire in Mediterranean-type ecosystems. Herbivores play an important role in controlling postfire seedling establishment, but their influence on regeneration by resprouting is less well known. To study the effects of fire intensity on resprouting of Adenostoma fasciculatum in southern California chaparral, and its interaction with herbivory, we conducted an experimental burn at three levels of fire intensity. We found that increasing fire intensity increased plant mortality, reduced the number of resprouts per plant, and delayed the time of resprouting. Herbivory increased with fire intensity, and was related to the time of resprouting. Plants resprouting later in the season and out of synchrony with the main flush were attacked more readily by herbivores. Post-resprouting mortality also increased with fire intensity and was significantly associated with herbivory in the higher fire intensity plots. Fire intensity effects on chaparral regeneration by resprouting may be farreaching through effects on the population structure, resprout production, and growth of Adenostoma fasciculatum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320621
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  • 8
    Electronic Resource
    Electronic Resource
    Differential sensitivities to glucose and galactose repression of gluconeogenic and respiratory enzymes from Saccharomyces cerevisiae (1985)
    Springer
    Archives of microbiology 143 (1985), S. 216-219 
    Details
    ISSN: 1432-072X
    Keywords: Isocitrate lyase ; Induction ; Catabolite repression ; Catabolite inactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The synthesis of isocitrate lyase was induced by the presence of ethanol in the chemostat reaching a specific activity of 200 mU·mg-1 at this induced state. In glucoselimited, derepressed cells, 20 mU·mg-1 were detected and under repressed conditions isocitrate lyase activity was not detected. The sensitivity of gluconeogenic enzymes: cytoplasmic malate dehydrogenase; fructose 1,6-bisphosphatase and isocitrate lyase as well as the mitochondrial enzymes NADH dehydrogenase and succinate cytochrome c oxidase to glucose and galactose repression were studied in chemostat cultures. Our results show that galactose was less effective as a repressor than glucose. Malate dehydrogenase was completely inactivated by glucose, whereas galactose only produced a 78% decrease of specific activity. Fructose 1,6-bisphosphatase and isocitrate lyase were completely inactivated by both sugars but at different rate. Glucose produced an 85% decrease of specific activity of the mitochondrial enzymes whereas galactose only decrease an 67%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00411238
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  • 9
    Electronic Resource
    Electronic Resource
    Transient responses of yeast continuous cultures to qualitative changes in the nutrient supply. Induction and repression of the galactose pathway enzymes (1983)
    Springer
    Archives of microbiology 135 (1983), S. 115-119 
    Details
    ISSN: 1432-072X
    Keywords: Induction ; Catabolic repression ; galactose metabolism ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Induction and repression kinetics of alphagalactosidase, galactose uptake system and Leloir pathway enzymes were studied in chemostat cultures by changing the medium feed from glucose (11 mM) to glucose and galactose (11 mM; 17 mM respectively) in the induction experiments; and from galactose (11 mM) or (111 mM) to galactose plus glucose (83 mM) in the repression experiments. Basal levels of alpha-galactosidase and glucose uptake could be estimated in glucose-limited yeast cells, but it was not possible to detect any glactose pathway enzyme activity. In the repression experiments under galactose-limited or galactose-sufficient yeast cells, alpha-galactosidase and galactokinase decayed with K d=-0.21h-1=-D; that is, synthesis of these enzymes ceased (catabolite repression). In contrast transferase and epimerase activities and galactose uptake, decreased with K d values of-0.33 and-0.54h-1, showing that these activities were also subject to catabolite inactivation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408019
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  • 10
    Electronic Resource
    Electronic Resource
    Recording mitotic chromosome cycle induction in living plant cells (1981)
    Springer
    Protoplasma 107 (1981), S. 189-194 
    Details
    ISSN: 1615-6102
    Keywords: Haemanthus katberinae Bak ; Induction ; Chromosome condensation ; Mitosis ; Time-lapse cinematography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The presence of a prophase nucleus inHaemanthus endosperm happens to trigger the break down of the nuclear envelope in any interphase nucleus, located in its close proximity. Besides, chromosomes in the interphase nucleus start condensing gradually for the initial breaking point which is the nearest point to the prophase. The observation suggest the diffusion of an inducer, whose progression has been recorded to occur at a rate of 1.1 μm/min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01275617
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