title: beta-Sulfur substituted alpha-ketoglutarates as inhibitors and alternate substrates for isocitrate dehydrogenases and certain other enzymes.
abstract: The RS-isomers of beta-mercapto-alpha-ketoglutarate, beta-methylmercapto-alpha-ketoglutarate and beta-methylmercapto-alpha-hydroxyglutarate have been synthesized. Beta-Mercapto-alpha-ketoglutarate was a potent inhibitor, competitive with isocitrate and noncompetitive with NADP+, of the mitochondrial NADP-specific isozyme from pig heart (Ki = 5 nM; Km (DL-isocitrate)/Ki(RS-beta-mercapto-alpha-ketoglutarate) = 650) and pig liver, the cytosolic isozyme from pig liver (I0.5 = 23 nM), and the NADP-linked enzymes from yeast (Ki = 58 nM) and Escherichia coli (Ki = 58 nM) at pH 7.4 and with Mg2+ as activator. beta-Mercapto-alpha-ketoglutarate was also an effective inhibitor of NADP-isocitrate-dehydrogenase activity in intact liver mitochondria. beta-Mercapto-alpha-ketoglutarate was a much less potent inhibitor for heart NAD-isocitrate dehydrogenase (Ki = 520 nM) than for the NADP-specific enzyme. beta-Methylmercapto-alpha-ketoglutarate (I0.5 = 10 microM) was a much less effective inhibitor than the beta-mercapto derivative for heart NADP-isocitrate dehydrogenase. The beta-sulfur substituted alpha-ketoglutarates were substrates for the oxidation of NADPH by heart NADP-isocitrate dehydrogenase without requiring CO2. beta-Methylmercapto-alpha-hydroxyglutarate, the expected product of reduction of beta-methylmercapto-alpha-ketoglutarate, did not cause reduction of NADP+ but it was an inhibitor competitive with isocitrate for NADP-isocitrate dehydrogenase. The beta-sulfur substituted alpha-ketoglutarate derivatives were alternate substrates for alpha-ketoglutarate dehydrogenase and the cytosolic and mitochondrial isozymes of heart aspartate aminotransferase but had no effect on glutamate dehydrogenase or alanine aminotransferase.
mesh_terms: D000818:Animals; D002384:Catalysis; D002417:Cattle; D002855:Chromatography, Thin Layer; D007521:Isocitrate Dehydrogenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology*; D008929:Mitochondria, Heart / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D011817:Rabbits; D013379:Substrate Specificity; D013455:Sulfur / Q000494:pharmacology; D013552:Swine
chemical_list: D007656:Ketoglutaric Acids; D013455:Sulfur; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+)