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  • 1980-1984  (2)
  • 1
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Phosphoenolpyruvate carboxykinase from four facultative anaerobic invertebrate species is shown to decarboxylate oxalacetate to phosphoenolpyruvate (Table 1). Knowledge of this reaction is of importance in the evaluation of gluconeogenic capacities of these organisms. 2. InTubifex the PEPCK-catalyzed decarboxylation reaction was characterized and its regulatory properties were studied. PEPCK mainly occurs in the cytosolic fraction and its absolute requirements in the decarboxylation direction are oxalacetate, Mn2+, nucleoside triphosphate (ITP) (Table 2). The pH optima for PEPCK-catalyzed decarboxylation and carboxylation reactions are 8.1 and 7.1, respectively (Fig. 1).K m values for oxalacetate and ITP were 0.25 and 0.39 mM, respectively (Fig. 2b and c). In presence of 0.5 mM AMP, the decarboxylation reaction was inhibited up to 50% of the control while even in presence of 5 mM AMP, the carboxylation reaction was unaffected (Fig. 3). Lombricine phosphate, one of the naturally occurring phosphagens inTubifex, activates the PEPCK-catalyzed decarboxylation reaction. 3-Mercaptopicolinic acid, a known specific inhibitor of vertebrate and invertebrate PEPCKs, also inhibitsTubifex PEPCK (Table 3). 3. UnlikeCrassostrea andAscaris, pyruvate carboxylase activity is present inTubifex tissues which will facilitate the conversion of C3 to C4 compounds and thus their eventual incorporation into glycogen. 4. Various gluconeogenic precursors when provided exogenously under aerobic conditions are incorporated into tissue glycogen by the intactTubifex (Table 4). 5. The potential roles of PEPCK regulatory properties under aerobic and anaerobic conditions are discussed with relation to gluconeogenesis and glycolysis inTubifex.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester, West Sussex : Wiley-Blackwell
    ISSN: 0170-4214
    Keywords: Mathematics and Statistics ; Applied Mathematics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The method of “cone iteration”; is used to obtain exact bounds for the solutions of a class of nonlinear operator equations. The general theory is applied to the problem of finding radially symmetric solutions of the plasma problem in the unit circle. Existence and uniqueness results are obtained at the same time. Some numerical examples demonstrate the method's high degree of accuracy.
    Type of Medium: Electronic Resource
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