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  • 1
    Electronic Resource
    Electronic Resource
    Effects of phosphoenolpyruvate, other glycolytic intermediates and methylxanthines on calcium uptake by a mitochondrial fraction from rat pancreatic islets (1978)
    Springer
    Diabetologia 15 (1978), S. 173-180 
    Details
    ISSN: 1432-0428
    Keywords: Islets of Langerhans ; insulin ; glucose ; phosphoenolpyruvate ; substrate-site ; methylxanthines ; cyclic AMP ; calcium ; mitochondria ; fructose 1,6-diphosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 45Ca2+-accumulation by a mitochondrial fraction from isolated rat pancreatic islets was strongly stimulated by ATP. The ATP-dependent uptake was inhibited by phosphoenolpyruvate in a dose-dependent manner over a wide variety of conditions. Inhibition by phosphoenolpyruvate was noncompetitive with respect to calcium, competitive with respect to magnesium, and antagonised by high Mg-ATP2− concentrations; fructose 1,6-diphosphate also decreased 45Ca2+-uptake. Other glucose metabolites were either less effective or ineffective in diminishing mitochondrial 45Ca2+-accumulation. The ATP-dependent uptake was also inhibited by xanthine derivatives (caffeine and 3-isobutyl-l-methylxanthine) which potentiate the effects of glucose on insulin secretion. Cyclic AMP had no effect. It is thought that the rate of insulin secretion is a function of the cytosolic calcium concentration in the B-cell. These data show that phosphoenolpyruvate, fructose 1,6-diphosphate and methylxanthines might influence exocytosis by direct effects on mitochondrial calcium accumulation, and thus the intracellular distribution of calcium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00421235
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Phosphoenolpyruvate in rat pancreatic islets: A possible intracellular trigger of insulin release? (1977)
    Springer
    Diabetologia 13 (1977), S. 481-486 
    Details
    ISSN: 1432-0428
    Keywords: Islets of Langerhans ; insulin ; glucose ; glyceraldehyde ; phosphoenolpyruvate ; glucoreceptor ; substrate-site ; regulator-site ; pyruvate kinase ; mannoheptulose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The content of phosphoenolpyruvate (PEP) has been measured in isolated rat islets of Langerhans incubated in vitro. Islet PEP was higher in islets incubated with 16.7 mmol/l glucose than in islets incubated with zero or 2.8 mmol/l glucose. Islet PEP content was also increased in islets incubated with 5 mmol/l D-glyceraldehyde. Mannoheptulose abolished the glucose-induced rise in PEP content but not that elicited by D-glyceraldehyde. These results are consistent with a role for PEP as an intracellular mediator of glucose- and glyceraldehyde-induced insulin release. The kinetics of pyruvate kinase in extracts of rat islets were studied. The maximal extractable activity was considerably higher than known rates of glycolytic flux. The Km values were found to be 0.16 mmol/l for PEP and 0.5 mmol/l for ADP. The control of islet PEP content and the possible role of PEP in insulin release are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01234500
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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