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  • Articles  (9)
  • kinetics
  • Springer  (9)
  • American Meteorological Society
  • 1995-1999  (5)
  • 1985-1989  (4)
  • 1965-1969
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  • 1996  (5)
  • 1987  (4)
  • Medicine  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nutrition 26 (1987), S. 125-137 
    ISSN: 1436-6215
    Keywords: vitamin C ; functions ; kinetics ; pool ; saturation ; requirements ; RDA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Zusammenfassung Die Bedeutung von Vitamin C für den menschlichen Organismus wird aus den wichtigen Funktionen ersichtlich, an denen das Vitamin beteiligt ist, wie zum Beispiel Kollagen- und Karnitinsynthesen. In neuerer Zeit entdeckt wurde seine Rolle bei der Noradrenalinsynthese, der Inaktivierung von freien Radikalen sowie der Verhinderung der Nitrosaminbildung. Die Vielfalt dieser Vitamin-C-abhängigen Funktionen läßt erkennen, daß die Bedarfsfestsetzung für Vitamin C nicht nur die Verhütung der Mangelkrankheit Skorbut anvisieren, sondern auch berücksichtigen sollte, daß alle diese Funktionen jederzeit genügend Vitamin C zur Verfügung haben müßten, um optimal reagieren zu können. Das Konzept der Gewebesättigung kommt diesem Ziel am nächsten. Studien mit einem kinetischen Modell haben ergeben, daß eine Sättigung mit täglicher Einnahme von 100 mg Vitamin C bei Nichtrauchern und von 140 mg bei Rauchern eintritt, Mengen, die als optimale Werte gelten können. Bei verschiedenen Krankheiten dürfte der Bedarf höher sein; die genauen Mengen müssen jedoch erst noch ermittelt werden.
    Notes: Summary The importance of vitamin C is reflected in its multifunctional roles which include participation in collagen and carnitine syntheses, promotion of iron absorption and the more recently discovered participation in noradrenaline synthesis, inactivation of free radical chain reactions, prevention of N-nitroso compound formation and more. Given the many extra-antiscorbutic functions of the vitamin, the Recommended Dietary Allowances (RDA) should not just prevent deficiency disease but should aim at providing sufficient amounts for all vitamin C-dependent functions to operate at full capacity. The concept of vitamin C tissue saturation is best able to meet this demand. The use of kinetic models has shown that the body pool is saturated with a daily intake of 100 mg vitamin C in non-smokers and 140 mg in smokers, amounts that may be regarded as optimal RDA values. Certain disease states may be accompanied by still higher vitamin C requirements but the exact amounts are not yet known.
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  • 2
    ISSN: 1432-1041
    Keywords: Key words Diphemanil methylsulphate ; Neonate; antimuscarinic agent ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 156 (1996), S. 93-100 
    ISSN: 1573-4919
    Keywords: rat liver nucleus ; oxalate binding protein ; histone III ; purification ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The rat liver nuclear oxalate binding protein was isolated, purified by anion and cation exchange column chromatography using Diethyl Amino Ethyl Sephadex, Carboxy Methyl Cellulose and Carboxy Methyl Sephadex C-50 ion exchangers. The purified oxalate binding protein was found to be H1B of H1 fraction of histories. Kinetic analysis of oxalate binding showed the presence of two affinity sites, one with Kd of 133.5 nM and Bmax of 40 pmoles and another with Kd of 262.5 nM and Bmax of 210 pmoles. The optimal oxalate binding was at pH 4.2 and at 28°C. The oxalate binding was specific and reversible and not due to ionic charge interaction. The IC50 of other dicarboxylates was higher than that of oxalate. EGTA had no effect on oxalate binding but di- and tri-carboxylate carrier inhibitors and thiol modifying agents significantly lowered the binding activity. Oxalate binding to histones was significantly reduced in the presence of DNA or nucleotides, but RNA had no effect. ATP completely inhibited the oxalate binding activity at 1 mM concentration. Different tissues exhibited oxalate binding showing ubiquitous nature. Calf thymus H1 showed maximal binding similar to liver histones.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 76 (1987), S. 45-54 
    ISSN: 1573-4919
    Keywords: DNA methyltransferase ; hemimethylated DNA ; kinetics ; affinity chromatography ; (rat liver)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract DNA substrate analogs were constructed from poly(dC-dG), M13, and XP12 DNA which do not contain a mixture of types of methylation sites. These were used to distinguish different kinetic mechanisms for maintenance and de novo methylation using a highly purified rat liver DNA (cytosine-5)-methyltransferase (DMase−) preparation. De novo methylation on single (ss) and double-stranded (ds) DNA was found to obey Michaelis-Menten kinetics while methylation of hemimethylated sites showed differences depending on size of the hemimethylated region. On long stretches analogous to maintenance methylation of newly replicated DNA, saturation could not be achieved and the kinetics showed non-ideal positive cooperative kinetics, while short stretches showed non-Michaelis-Menten kinetics and rapid saturation. Two types of DMase-DNA complexes could be distinguished by means of affinity chromatography on DNA-agarose matrices and in preincubation assays. The later complex, which is engaged in methyl group turnover, exhibited enhanced stability. The competitiveness of variously configured DNAs was found to parallel the stability of complex formation, e.g., ss, hemi- and ds DNA, respectively. In studies utilizing 5-bromodeoxyuridine, the thymine analog left the basic reaction mechanisms unchanged but increased the km and S0.5 while reducing the velocity of these reactions.
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  • 5
    ISSN: 1573-4919
    Keywords: acetylcholinesterase ; kinetics ; inhibition ; methotrexate ; anticancer drugs ; human erythrocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This work addresses the kinetic analysis of the interaction of methotrexate (MTX) with human erythrocyte membrane-bound acetylcholinesterase (AChE, EC 3.1. 1.7). It was found that the MTX effect was independent of time of incubation with AChE before the addition of substrate which proves its reversible action. The IC50 was determined, by three methods, to be 0.73 mM. The Michaelis-Menten constant (Ks) for the hydrolysis of acetylthiocholine iodide (ASCh) by AChE was 0.13 mM in the control system, a value decreased by 30–61% in the MTX treated systems. The Vmax was 1.27μtmole/min/mg protein for the control system while it was decreased by 44–77% in the MTX treated systems. The Linexveaver-Buck plot, Dixon plot, and their secondary replots indicated that the nature of the inhibition was of the linear mixed type, i.e. uncompetitive and noncompetitive. The values of Ki(slope) and KI(tntecept) were estimated as 1.67 and 0.34 mM, respectively.
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  • 6
    ISSN: 1573-0778
    Keywords: hybridomas ; serum-free medium ; monoclonal antibodies ; reactor series ; kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Hybridomas were cultured under steady-state conditions in a series of two continuous stirred-tank reactors (CSTRs), using a serum-free medium. The substrate not completely converted in the first CSTR, was transported with the cells to the second one and very low growth rates, high death rates, and lysis of viable cells were observed in this second CSTR. These conditions are hardly accessible in a single vessel, because such experiments would be extremely time-consuming and unstable due to a low viability. In contrast to what is often observed in literature, kinetic parameters could thus be derived without the neccessity for extrapolation to lower growth rates. Good agreement with literature averages for other hybridomas was found. Furthermore, showing that the reactor series is a valuable research tool for kinetic studies under extreme conditions, the possibility to observe cell death under stable and defined steady-state conditions offers interesting opportunities to investigate apoptosis and necrosis. Additionally, a model was developed that describes hybridoma growth and monoclonal antibody production in the bioreactor cascade on the basis of glutamine metabolism. Good agreement between the model and the experiments was found.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of experimental biology and medicine 103 (1987), S. 660-662 
    ISSN: 1573-8221
    Keywords: hydrogenated phenazepam analog ; metabolism ; kinetics ; excretion ; differences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Mycopathologia 98 (1987), S. 179-184 
    ISSN: 1573-0832
    Keywords: adhesion ; C. albicans ; kinetics ; concanavalin A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The early in vitro kinetics of Candida albicans attachment to human buccal epithelial cells was studied with the aid of an adhesion assay and solutions of concanavalin A (Con A), a lectin which is capable of inhibiting yeast adhesion. Various saccharides and putative receptor analogues were also tested. Solutions of each single reagent were added to tubes containing aliquots of mucosal cells and germinated yeasts at the beginning of a 1-hour incubation period (time O) or at 10 minute intervals during the assay. The number of yeasts attached to 200 mucosal cells was subsequently determined microscopically. Yeast adhesion remained constant following addition of phosphate-buffered saline (PBS) at time 0 or at any time thereafter. However, addition of Con A at 0, 10 or 20 minutes of incubation decreased adhesion significantly to 38%, 45% and 63% of control values. This inhibitory effect dwindled as time of incubation prior to lectin addition increased and Con A could not inhibit adhesion significantly after twenty minutes. Results obtained with Con A using live germinated yeasts were similar to those obtained with formalin-killed C. albicans. The other reagents tested failed to decrease adhesion significantly. These included the putative receptor analogues fibronectin, N-acetyl-d-glucosamine and d-galactose, and several non-specific saccharides such as α-d-methylglucopyranoside, d-ribose and d-xylose. It is suggested that in vitro attachment to human mucosal cells by C. albicans is inhibitable up to a defined point in time by a lectin with affinity for mannosecontaining surface moieties, but becomes non-reversible thereafter. This experimentally-observed irreversibility is independent of yeast cell viability.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of experimental biology and medicine 121 (1996), S. 329-330 
    ISSN: 1573-8221
    Keywords: erythropoiesis ; kinetics ; cell death
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The fundamental patterns of influence of the localization of erythroid cell death on cell kinetics are defined with the aid of mathematical modeling. It is established that the kinetic picture is mainly dictated by the region where the death is localized.
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