Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.4.1.1 (pyruvate carboxylase)
 1,516 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In islet beta-cells and INS-1 cells both the high activity of malic enzyme and the correlation of insulin secretion rates with pyruvate carboxylase (PC) flux suggest that a pyruvate-malate cycle is functionally relevant to insulin secretion. Expression of the malic enzyme isoforms in INS-1 cells and rat islets was measured, and small interfering RNA was used to selectively reduce isoform mRNA expression in INS-1 cells to evaluate its impact on insulin secretion. The cytosolic NADP(+)-specific isoform (ME1) was the most abundant, with the mitochondrial isoforms NAD(+)-preferred (ME2) expressed at approximately 50%, and the NADP(+)-specific (ME3) at approximately 10% compared with ME1. Selective reduction (89 +/- 2%) of cytosolic ME1 mRNA expression and enzyme activity significantly reduced glucose (15 mM:41 +/- 6%, p < 0.01) and amino acid (4 mM glutamine +/- 10 mM leucine: 39 +/- 6%, p < 0.01)-stimulated insulin secretion. Selective small interfering RNA reduction (51 +/- 6%) of mitochondrial ME2 mRNA expression did not impact glucose-induced insulin secretion, but decreased amino acid-stimulated insulin secretion by 25 +/- 4% (p < 0.01). Modeling of the metabolism of [U-(13)C]glucose by its isotopic distribution in glutamate indicates a second pool of pyruvate distinct from glycolytically derived pyruvate in INS-1 cells. ME1 knockdown decreased flux of both pools of pyruvate through PC. In contrast, ME2 knockdown affected only PC flux of the pyruvate derived from glutamate metabolism. These results suggest a physiological basis for two metabolically and functionally distinct pyruvate cycles. The cycling of pyruvate by ME1 generates cytosolic NADPH, whereas mitochondrial ME2 responds to elevated amino acids and serves to supply sufficient pyruvate for increased Krebs cycle flux when glucose is limiting.
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PMID:Cytosolic and mitochondrial malic enzyme isoforms differentially control insulin secretion. 1710 38

NAD(P)-malic enzyme (NAD(P)-ME) catalyzes the reversible oxidative decarboxylation of malate to pyruvate, CO2 , and NAD(P)H and is present as a multigene family in Arabidopsis thaliana. The carboxylation reaction catalyzed by purified recombinant Arabidopsis NADP-ME proteins is faster than those reported for other animal or plant isoforms. In contrast, no carboxylation activity could be detected in vitro for the NAD-dependent counterparts. In order to further investigate their putative carboxylating role in vivo, Arabidopsis NAD(P)-ME isoforms, as well as the NADP-ME2del2 (with a decreased ability to carboxylate pyruvate) and NADP-ME2R115A (lacking fumarate activation) versions, were functionally expressed in the cytosol of pyruvate carboxylase-negative (Pyc- ) Saccharomyces cerevisiae strains. The heterologous expression of NADP-ME1, NADP-ME2 (and its mutant proteins), and NADP-ME3 restored the growth of Pyc- S. cerevisiae on glucose, and this capacity was dependent on the availability of CO2 . On the other hand, NADP-ME4, NAD-ME1, and NAD-ME2 could not rescue the Pyc- strains from C4 auxotrophy. NADP-ME carboxylation activity could be measured in leaf crude extracts of knockout and overexpressing Arabidopsis lines with modified levels of NADP-ME, where this activity was correlated with the amount of NADP-ME2 transcript. These results indicate that specific A. thaliana NADP-ME isoforms are able to play an anaplerotic role in vivo and provide a basis for the study on the carboxylating activity of NADP-ME, which may contribute to the synthesis of C4 compounds and redox shuttling in plant cells.
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PMID:Specific Arabidopsis thaliana malic enzyme isoforms can provide anaplerotic pyruvate carboxylation function in Saccharomyces cerevisiae. 2807 62