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  • Articles  (95)
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  • 2020-2024  (21)
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  • 1995-1999  (77)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2818-2828 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper presents an approach based on the saddle-point approximation to study the equilibrium interactions between small molecules and macromolecules with a large number of sites. For this case, the application of the Darwin–Fowler method results in very simple expressions for the stoichiometric equilibrium constants and their corresponding free energies in terms of integrals of the binding curve plus a correction term which depends on the first derivatives of the binding curve in the points corresponding to an integer value of the mean occupation number. These expressions are simplified when the number of sites tends to infinity, providing an interpretation of the binding curve in terms of the stoichiometric stability constants. The formalism presented is applied to some simple complexation models, obtaining good values for the free energies involved. When heterogeneous complexation is assumed, simple expressions are obtained to relate the macroscopic description of the binding, given by the stoichiomeric constants, with the microscopic description in terms of the intrinsic stability constants or the affinity spectrum. © 1999 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1503-1505 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intrinsic "self-trapped" hole center in KD2PO4 crystals has been identified using electron paramagnetic resonance and electron-nuclear double resonance. These defects, labeled [D2PO4]o centers, can be formed at 77 K by irradiating with either 60 kV x rays or the fourth harmonic (266 nm) of a pulsed Nd:YAG laser. The hole is equally shared by two adjacent oxygen ions, and hyperfine interactions with one phosphorus and two equivalent deuterons are observed. The sample used in this investigation was approximately 80% deuterated, thus both [D2PO4]o and [HDPO4]o centers were detected, with the former being dominant. These intrinsic self-trapped hole centers are of interest because of their potential role in the transient optical absorption produced in KD2PO4 crystals at room temperature by intense 266 nm laser pulses. © 1999 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 45 (1998), S. 0 
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Degenerate primers for two regions of sequence homology in the myosin head domain were used in a polymerase chain reaction screen of Tetrahymena thermophila genomic DNA to amplify a 765 bp fragment that was cloned and sequenced. Based on the presence of conserved, myosin-specific sequences, the 765 bp PCR product was identified as a fragment of a myosin gene, the first to be discovered in ciliated protozoa and herein referred to as MYO1. An inverse polymerase chain reaction strategy was used to obtain additional sequence data that included the entire head domain of MYO1. Alignment of the predicted amino acid sequence of the MYO1 head domain with known myosin sequences identified the ATP-binding site, a phosphorylation site, and other myosin-specific consensus regions. In a northern blot analysis, a 765 bp MYO1-specific probe detected a 6.6 kb transcript under highly stringent hybridization conditions. Phylogenetic analysis revealed that the predicted protein encoded by MYO1 is not a member of any of the previously defined myosin classes and therefore represents a presumptive new myosin class.
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  • 4
    ISSN: 1432-2048
    Keywords: Key words: Acyl-acyl carrier protein thioesterase ; Fatty acid synthetase II ; Helianthus (seed) ; β-keto-acyl-acyl carrier protein synthetase II ; Mutant fatty acid ; Palmitic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Two high-palmitic acid sunflower (Helianthus annuus L.) mutants, CAS-5 and CAS-12, have been biochemically characterised. The enzymatic activities found to be responsible for the mutant characteristics are β-keto-acyl-acyl carrier protein synthetase II (KASII; EC 2.3.1.41) and acyl-acyl carrier protein thioesterase (EC 3.1.2.14). Our data suggest that the high-palmitic acid phenotype observed in both mutant lines is due to the combined effect of a lower KASII activity and a higher thioesterase activity with respect to palmitoyl-acyl carrier protein (16:0-ACP). The level of the latter enzyme appeared to be insufficient to hydrolyse the produced 16:0-ACP completely. As a consequence of this, three new fatty acids appear: palmitoleic acid (16:1 Δ9), asclepic acid (18:1 Δ11), and palmitolinoleic acid (16:2 Δ9 Δ12). These fatty acids should be synthesised from palmitoyl-ACP or a derivative by the action of the stearoyl-ACP desaturase, fatty acid synthetase II and oleoyl-phosphatidylcholine desaturase, respectively.
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  • 5
    ISSN: 1432-2048
    Keywords: Key words:Helianthus (seed) ; Microsome ; Oil body ; Oleate desaturase ; Temperature adaptation ; Triacylglycerol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In-vivo experiments with developing sunflower (Helianthus annuus L.) seeds demonstrated that oleate desaturase activity was stimulated by low temperature (10 °C), repressed by high temperature (30 °C) and rapidly restored by returning the seeds to low temperature. Within time periods of 2–4 h, in which the de-novo fatty acid synthesis was negligible, the percentages of oleate (18:1) and linoleate (18:2) were modified in the seed lipids as a consequence of temperature adaptation. When the seeds were transferred to low temperature, the 18:2 content increased in all lipids from both microsomal membranes and oil bodies. After shifting to high temperature, the overall 18:2 content remained constant, but the 18:2 content decreased in diacylglycerols, phosphatidylcholine (PC) and other polar lipids of the two fractions and also in triacylglycerols (TAGs) of the microsomes but increased in TAGs of the oil bodies. The results indicate that the mechanism for the rapid adaptation of sunflower seeds to temperature changes involves (i) the synthesis or activation of oleate desaturase at low temperature and the reversible inhibition of this enzyme at high temperature and (ii) the exchange of 18:1 and 18:2 between TAGs and PC. Under both low and high temperature, 18:1 is transferred from reserve TAGs to PC and 18:2 is transferred from PC to reserve TAGs. At low temperature, 18:1 is desaturated to 18:2 thus allowing the enrichment of membrane lipids with 18:2, the excess being stored in reserve TAGs. At high temperature, however, and provided that oleate desaturase is repressed, the membrane lipids become enriched in 18:1 and the oil-body TAGs become enriched in 18:2.
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 192-194 (Aug. 1995), p. 907-0 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
    ISSN: 1432-0827
    Keywords: Key words: Human osteoblastic cells — Skeletal site — Aging.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Bone loss with aging may be due, at least in part, to inadequate bone formation. Moreover, the process of bone aging is known to follow a different pattern throughout the skeleton. In this study, we examined the cell proliferation rate (area under the cell growth curve, AUC) and the secretion of C-terminal type I procollagen (PICP), alkaline phosphatase (ALP), and osteocalcin (OC) in primary cultures of osteoblastic cells from human trabecular bone. Osteoblastic cells were obtained for 168 donors (100 women and 68 men). Ninety-eight bone samples were obtained from subjects undergoing knee arthroplastia, 52 aged 50–70 years (64 ± 5) and 46 over age 70 (73 ± 2). Another 70 bone samples were obtained from subjects undergoing hip arthroplastia; 51 were 50–70 years old (64 ± 4) and 19 were over 70 (75 ± 5). Osteoblastic cells from the older donors had a lower proliferation rate and OC secretion than those from younger subjects. However, ALP secretion was higher in the former subjects, whereas PICP secretion was unchanged. Osteoblastic cells from hip had a lower proliferation rate than those from knee. PICP secretion was also lower and ALP secretion was higher in the former cells. In age-matched cell cultures, osteoblastic cells from the knee had higher proliferation rate and PICP secretion than osteoblastic cells from the hip. However, ALP secretion was lower in knee osteoblastic cells than those from hip only in the younger group. With aging, ALP secretion was found to increase in knee osteoblactic cells, whereas OC secretion decreased in osteoblastic cell cultures from the hip. Our findings suggest that bone loss with aging may be accounted for, at least in part, by a decreased osteoblastic cell proliferation and an increased osteoblastic maturation. In addition, our data indicate that these changes with aging do not occur similarly at different skeletal sites.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 60 (1997), S. 391 -393 
    ISSN: 1432-0827
    Keywords: Key words: Bone growth — Fractures — Osteotomy.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. One hundred and five 5-week-old male rats were used to study the influence of the stability of an osteotomy on longitudinal overgrowth of the bone. In 45 rats (Group 1) a transverse diaphyseal osteotomy of the right tibia was made; the left tibia was left untreated. In the second 45 rats (Group 2) the right tibia was osteotomized after applying an external fixator; the left tibia underwent a sham operation without osteotomy. Fifteen further rats (Group 3) were used as a nonoperated control group. After being measured at different periods up to 20 weeks, the osteotomized tibiae of the Group 1 (unstable) were 16–25% longer than those of their nontreated limbs (P 〈 0.001). The osteotomized tibiae of the Group 2 (stable) were 6–11% longer than those of the sham-operated opposite limbs (P 〈 0.001). The osteotomized and unstable tibiae were 9–17% longer than the osteotomized and stable tibiae (P 〈 0.001) throughout the whole study. Although several factors have been considered to be responsible for longitudinal bone overgrowth after fracture in young animals, this work suggests that bone's stability plays a decisive role in the final outcome.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 98 (1999), S. 496-501 
    ISSN: 1432-2242
    Keywords: Key words Helianthus annuus ; Sunflower mutant ; Palmitic acid ; Inheritance ; Fatty acid composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Sunflower genotypes with increased levels of palmitic acid (C16 : 0) in the seed oil could be useful for food and industrial applications. The objective of the present study was to determine the inheritance of the high C16 : 0 content in the sunflower mutant line CAS-5 (〉25% of the total oil fatty acids). This mutant was reciprocally crossed with the lines HA-89 (5.7% C16 : 0) and BSD-2-691 (5.4% C16 : 0), the latter being the parental line from which CAS-5 was isolated. No maternal effect for the C16 : 0 content was observed from the analysis of F1 seeds in any of the crosses. The inheritance study of the C16 : 0 content in F1, F2 and BC1F1 seeds from the crosses of CAS-5 with its parental line BSD-2-691 indicated that the segregation fitted a model of two alleles at one locus with partial dominance for the low content. The analysis of the fatty acid composition in the F2 populations from the crosses with HA-89 revealed a segregation fitting a ratio 19 : 38 : 7 for low (〈7.5%), middle (7.5–15%), and high (〉25%) C16 : 0 content, respectively. This segregation was explained on the basis of three loci (P1, P2, P3) each having two alleles showing partial dominance for low content. The genotypes with a high C16 : 0 content were homozygous for the recessive allele p1 and for at least one of the other two recessive alleles, p2 or p3. This model was further confirmed with the analysis of the F3 and the BC1F1 generations. It was concluded that both the recessive alleles p2 and p3 were already present in the BSD-2-691 line, the allele p1 being the result of a mutation from P1. This genetic study will facilitate breeding strategies associated with the incorporation of the high C16 : 0 trait into agronomically acceptable sunflower hybrids.
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  • 10
    ISSN: 1573-0417
    Keywords: sedimentology ; saline lake ; meromixis ; Northern Great Plains ; Holocene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Medicine lake is a small (about 1 km2), shallow (up to 10 m deep), saline (50–170 g l−1) and meromictic lake formed after the retreat of the Wisconsin ice in the north American Great Plains. Based on a detailed sedimentological analysis of cores, we describe and interpret 13 sedimentary subfacies grouped in 9 associations which characterize the following lacustrine subenvironments: clastic littoral (freshwater and saline), springs, microbial mats, bench slope, and pelagial (oxic, alternating oxic-anoxic, anoxic and hypersaline, and organic-dominated). Lateral distribution and vertical evolution of subfacies in our model are controlled by climate fluctuations, climate-related limnological parameters (lake level, TDS and brine composition, and redox conditions), and autocyclic processes (progressive infilling of the basin and higher sedimentation rate in the pclagial realm). Microbial and chemical processes govern deposition in this system, and meromixis plays a decisive role in lake dynamics. Phototropic bacterial plate communites at the chemocline dominated as pelagial organic producers during stable meromictic periods, whereas benthic microbial communities developed during mixed water periods. Water stratification during the Holocene was mainly controlled by three parameters: 1) basin morphometry, 2) lake level, and 3) differences in TDS values between mixolimnion and monimolimnion waters. Sedimentary facies analyses is a powerful descriptive and interpretative tool that greatly contributes to deciphering the high resolution paleoenvironmental information archived in lake sequences. Depositional and paleoenvironmental models provide a dynamic framework for integrating paleolimnological data and other proxy paleorecords. Medicine lake serves as a facies model for shallow, perennial hypersaline, meromictic lakes in modern and ancient lacustrine basins. The sediment sequence from Medicine lake cores is consistent with the general paleoclimatic evolution of the northern Great Plains since the retreat of ice sheets. Our study reveals a plethora of rapid fluctuations in the water cycle both during the middle and the late Holocene. These augment prior paleoclimate reconstructions based on diatom studies of the lower Holocene freshwater to saline transition and on pollen profiles which show little variability during the subsequent long prairie grass episode.
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