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  • 1
    Electronic Resource
    Electronic Resource
    Molecular mechanics calculations of the noncovalent interaction of aflatoxin B1 and its ultimate carcinogen with various dna sequences (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 133-143 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular mechanics calculations have been used to study the external noncovalent complexes formed between DNA and the strong carcinogen, aflatoxin B1. Three different sequences of hexameric duplexes were used for the DNA. Both the aflatoxin B1 parent molecule and its ultimate carcinogenic form, a carbocation, were modeled. The results are compared with recent experimental data on sequence specificity of the covalent attachment of aflatoxin to sites on the nucleotide bases. The comparison is discussed in light of a recently proposed hypothesis suggesting that the locus of carbocation formation is in acidic domains near the surface of the macroion and this determines the site of covalent adduct formation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560381715
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular orbital studies of the hydrolysis reactions of benzo[a]pyrene diol epoxides (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 1-14 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic studies of the hydrolysis of benzo[a]pyrene diol epoxides have shown that hydrolysis proceeds through an acid-catalyzed SN1 mechanism and that the rate-determining step is the formation of a benzylic carbocation. The formation of this carbocation indicates that the diol epoxide can react with nucleophilic sites on DNA as an alkylating agent. Previous work has indicated that the kinetic data could be accurately fit to kobsd = kH [H+] + k0, in which kH [H+] is the pseudo first-order rate constant for acid-catalyzed hydrolysis and k0 is the rate constant for spontaneous hydrolysis. The observation made in several laboratories, that DNA catalyzes the hydrolysis of carcinogenic diol epoxides, is of direct interest in light of our recent calculation indicating that the local environment of DNA has a high concentration of hydrogen ions. The significance of acidic domains around nucleic acids is primarily in the ability of the protons to catalyze reactions. We have hypothesized that the high concentration of hydrogen ions at the DNA surface is responsible for the catalysis and that the generation of benzylic carbocations at the DNA surface can result in either nontoxic tetraols or in mutagenic nucleotide adducts, depending on the nucleophile with which the carbocation reacts. The calculations presented here are concerned with qualitatively understanding the rate constants in terms of the mechanisms of the acid-catalyzed and the spontaneous (H2O-catalyzed) hydrolyses. © 1992 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560440705
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  • 3
    Electronic Resource
    Electronic Resource
    Counterion condensation theory revisited: Limits on its applicability (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 213-230 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metropolis Monte Carlo and Poisson-Boltzmann calculations were done to quantitatively assess the conditions under which counterion condensation (CC) theory could be considered valid. The fundamental prediction of condensation theory, that the number of counterions bound to a polyelectrolyte molecule can be predicted by a single parameter describing the linear charge density of the charged system, was shown to be quantitatively correct for a range of conditions. To define the number of counterions bound, it was necessary to use an energy-based criterion by which ions that interact with the polyion with an energy less than -kT were considered bound. Using this criterion, Monte Carlo calculations on systems consisting of charged cylinders and a neutralizing number of counterions in a dielectric continuum showed that the number of bound counterions was quantitatively predictable by the CC relation (1-1/ξ) for systems with a linear charge density and dimensions approaching those of duplex or triplex DNA. Poisson-Boltzmann (PB) calculations on cylinders with different linear charge densities and radii have been done to assess the limits of the CC prediction that the number of counterions bound is a constant even as the bulk concentration of electrolyte in the surrounding is increased. As in the case of the MC calculations, the validity of the CC prediction is seen to increase with increasing linear charge density of the charged cylinder. The agreement between PB and CC is seen to be very good for highly charged cylinders. The results described here provide justification for the use of CC theory for interpreting experimental data on polyelectrolytes of the approximate dimensions and linear charge density of duplex or triplex DNA. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480722
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical predictions of the functional interactions of DNA and mutagenic aziridines (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 29-37 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aziridine analogues of the epoxide metabolites of carcinogenic polycyclic aromatic hydrocarbons have greater mutagenic potency than the epoxides. Like their well-studied analogues, the aziridines undergo a pH-dependent decomposition that leads to a reactive carbocation intermediate. In aqueous solution the nucleophile with which the carbocation generally reacts is water. The kinetics of this pH-dependent reaction have been experimentally characterized by others. Although the effect of DNA on this reaction has not been studied, we hypothesize that, like their epoxide analogues, the aziridine derivatives of polycyclic aromatic hydrocarbons undergo a DNA-catalyzed reaction leading through a carbocation to either a DNA-adduct or a hydrolysis product. Using Poisson-Boltzmann calculations in conjunction with Metropolis Monte Carlo simulations and energy-minimized conformations, we predict the DNA-dependence of the acidcatalyzed decomposition of the K-region aziridine, phenanthrene[9,10]imine. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560704
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  • 5
    Electronic Resource
    Electronic Resource
    New developments in computational polyelectrolyte theory (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 287-299 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A computational methodology for calculating the spatial distribution of average electrolyte ion density in the presence of a polyelectrolyte macroion is presented. The method makes use of an iterative solution technique previously applied to solve the three-dimensional Poisson-Boltzmann equation. Criteria are developed for determining the regions in space at which the Poisson-Boltzmann approximation fails. In these regions the formal series of sums of products describing the local probability densities is constructed. Accurate approximations to the series are developed. The result is a computationally feasible method that avoids the inaccuracies of Poisson-Boltzmann theory.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260730
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  • 6
    Electronic Resource
    Electronic Resource
    Porcine oocyte zona pellucida Mr 55,000 glycoproteins: Identification of O-glycosylated domains (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 33 (1992), S. 182-188 
    Details
    ISSN: 1040-452X
    Keywords: Glycopeptides ; O-linked oligosaccharides ; Jacalin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The distribution of O-linked oligosaccharides on the Mr 55,000 glycoproteins, ZP3α and ZP3, of the porcine oocyte zona pellucida was examined. Purified preparations of endo-β-galactosidase digested ZP3α and ZP3β were reduced and carboxamidomethylated and digested with trypsin. When the trypsin digests were mapped by HPLC, each glycoprotein yielded only one N-acetylgalactosamine containing glycopeptide. Purification of the O-glycopeptides was achieved by a two-step protocol. Tryptic digests were applied to jacalin-agarose and specifically-bound O-glycopeptides (αOGP and βOGP) were eluted with buffer containing 50 mM α-methylgalactoside as the haptenic sugar. Further purification of each O-glycopeptide was accomplished by reverse phase HPLC. Purified O-glycopeptides were characterized with respect to amino acid and carbohydrate compositions and sequenced by automated Edman degradation; αOGP was a 41-residue glycopeptide with three O-linked sugar chains. Sequence comparisons revealed a 75% identity between αOGP and a corresponding segment of rabbit rec55 zona protein; OGP was a 25-residue glycopeptide characterized by the presence of one N-linked and five O-linked sugar chains and a trypsin-resistant internal arginine residue. Sequence alignments revealed an 80% or greater identity between βOGP and internal peptides of mouse, hamster and human ZP3 zona proteins. These studies demonstrate that in the case of ZP3α and ZP3β, the pig homologues of rabbit rec55 and mouse ZP3, respectively, O-linked oligosaccharides are confined within delimited domains rather than widely dispersed on the polypeptide backbone. Such clustering of O-linked oligosaccharides may represent an essential determinant of the structure and biological activity of zona proteins. © 1992 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080330210
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  • 7
    Electronic Resource
    Electronic Resource
    Isolation and cultivation of blastocyst-derived stem cell lines from american mink (Mustela vison) (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 33 (1992), S. 418-431 
    Details
    ISSN: 1040-452X
    Keywords: Embryonic stem cells ; Cell differentiation ; Pluripotency ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Ten embryonic stem (ES) cell lines from mink blastocysts were isolated and characterized. All the lines had a normal diploid karyotype; of the ten lines studied, five had the XX and five had the XY constitution. Testing of the pluripotency of the ES-like cells demonstrated that (1) among four lines of genotype XX, an X was late-replicating in three; both Xs were active in about one-third of cells of line MES8, and analysis of glucose-6-phosphate dehydrogenase revealed no dosage compensation for the X-linked gene; (2) when cultured in suspension, the majority of lines were capable of forming “simple” embryoid bodies (EB), and two only showed the capacity for forming “cystic” multilayer EBs. However, formation of ectoderm or foci of yolk sac hematopoiesis, a feature of mouse ES ceils, was not observed in the “cystic” EB; (3) when cultured as a monolayer without feeder, the ES cells differentiated into either vimentin-positive fibroblast-like cells or cytokeratin-positive epithelial-like cells (less frequently); neural cells appeared in two lines; (4) when injected into athymic mice, only one of the four tested lines gave rise to tumors. These were fibrosarcomas composed of fibrobalst-like cells, with an admixture of smooth muscular elements and stray islets of epithelial tissue; (5) when the ES cells of line MES1 were injected into 102 blastocyst cavities and subsequently transplanted into foster mathers, we obtained 30 offspring. Analysis of the biochemical markers and coat color did not demonstrate the presence of chimaeras among offspring. Thus the cell lines derived from mink blastocysts are true ES cells. However, their pluripotential capacities are restricted. © 1992 Wiley-Liss, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080330408
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  • 8
    Electronic Resource
    Electronic Resource
    Porcine zona pellucida ZP3α glycoprotein mediates binding of the biotin-labeled Mr 55,000 family (ZP3) to boar sperm membrane vesicles (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 36 (1993), S. 382-389 
    Details
    ISSN: 1040-452X
    Keywords: Pig spermatozoa ; Sperm adhesive protein ; Competitive ligand binding assay ; Polylactosamines ; Fucoidin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The two Mr 55,000 glycoproteins, ZP3α and ZP3b̃, of porcine zona pellucida copurify as a preparation designated ZP3. Gamete binding assays have implicated ZP3α, but not ZP3b̃, as participating in sperm-zona recognition events. We now report that boar sperm contain membrane-associated binding sites with specificity for ZP3α. Biotin-labeled (b-) preparations of ZP3 bind to intact boar sperm in a saturable manner, with localization on the anterior head region. Membrane vesicles obtained from capacitated sperm by nitrogen cavitation retain b-ZP3 binding sites as determined by an enzyme-linked method employing alkaline phosphatase-conjugated strepavidin. In competitive binding assays using b-ZP3 (0.1μg/ml) as probe, heat-solubilized zonae and ZP3 were effective competitors, whereas the nonzona molecules fetuin and fucoidin were not. Digestion of ZP3 with endo-b̃-galactosidase, an enzyme that trims polylactosamines, enhanced its affinity for membrane receptors. In contrast treatments such as chemical deglycosylation, pronase digestion, or disruption of disulfide bonds abolished the ligand activity of ZP3. Finally, purified ZP3α was an at least 100-fold better antagonist than purified ZP3b̃. The results demonstrate that binding of b-ZP3 to isolated boar sperm membranes is mediated by sperm receptors with specificity for the ZP3α macromolecular component and reveal a complex contribution of both carbohydrate and protein moieties toward the ligand activity of this sperm adhesive zona molecule. © 1993 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080360315
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  • 9
    Electronic Resource
    Electronic Resource
    Isolation, composition, and biological activity of sugar chains of porcine oocyte zona pellucida 55K glycoproteins (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 30 (1991), S. 126-134 
    Details
    ISSN: 1040-452X
    Keywords: Egg envelope ; Peptide N-glycosidase F digestion ; Oligosaccharides ; Sulfated polylactosamines ; Sperm-zona binding ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: ZP3, a preparation of the 55K families of porcine oocyte zona pellucida, possesses carbohydrate-dependent ligand activity for boar sperm. The aim of the present study was to analyze ZP3 N- and O-linked oligosaccharides with respect to size distribution, composition, and role in sperm-zona recognition events. Digestion of denatured ZP3 with peptide N-glycosidase F (PNGaseF) released the majority of N-glycans which fractionated on Sephadex G-75 resin as a polydisperse population with apparent molecular masses ranging from 1,900-8,200 Da. The higher molecular weight N-glycans were characterized by the presence of strongly anionic sulfated/sialylated polylactosamine structures. Alkaline-borohydride treatment of the PNGaseF-digested core proteins liberated O-glycans as a heterogeneous population of oligosaccharide alcohols, which were fractionated on a Sephadex G-50 column. Compositional analyses indicated sulfated polylactosamine units associated with the higher molecular weight O-glycans. Preincubation of boar sperm with ZP3 or purified O-glycans, but not N-glycans, inhibited subsequent attachment to zona-encased oocytes. Purified O-glycans were, however, 2 to 3 orders of magnitude less effective than ZP3 as competitive ligands. The results document the extreme heterogeneity of the ZP3 carbohydrate moiety, in large part attributable to a board spectrum of variably sized N- and O-linked sulfated polylactosamines. Ligand competition bioassays suggest that O-glycans mediate, at least in part, the sperm adhesive properties of ZP3 and strongly imply that high-affinity interaction of ZP3 sugar chains with complementary sperm receptors is dependent upon their covalent association with core proteins.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080300209
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  • 10
    Electronic Resource
    Electronic Resource
    Estivation in Protopterus (1986)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 190 (1986), S. 237-248 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Estivation in Protopterus is an episodic event characterized by elaboration of a cocoon as ambient water is withdrawn, a state of torpor, and distinctive cardiorespiratory and metabolic changes. Among the more striking of these features is a decrease in oxygen consumption, a complete reliance on air breathing to satisfy metabolic need, a slowing of the heart rate, and a drop in blood pressure. The initiating mechanism for these dramatic changes is not known. As yet, specific “estivating factors” have not been identified. However, the pattern of decrease in oxygen uptake during estivation and starvation are quite similar, suggesting that a common factor may be involved in both. Attempts to implicate suppression of thyroid function in the onset of estivation have been unconvincing. Although initiating mechanisms for estivation in Protopterus remain uncertain, once estivation sets in a variety of adaptive changes occur that enable the estivating lungfish to survive for months to years without ingesting food or water. Among these are oliguria and a shift in metabolic pathways. Although estivation in Protopterus has been characterized with respect to cardiorespiratory and metabolic parameters, no attempt is made to extrapolate from the biologic processes in Protopterus to other lepidosirenid lungfish or to other genera.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1051900416
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