Alpha-methylisocitrate. A selective inhibitor of TPN-linked isocitrate dehydrogenase from bovine heart and rat liver

Abstract

Alpha-Methylisocitrate (3-hydroxy-1,2,3-butanetricarboxylate) is a potent inhibitor, competitive with isocitrate (1-hydroxy-1,2,3-propanetricarboxylate), of the TPN-linked isocitrate dehydrogenase from bovine heart and rat liver; it does not inhibit the DPN-specific enzyme from these tissues. In the presence of magnesium ion, values of Kis for DL-alpha-methylisocitrate for purified bovine heart enzyme, rat liver cytosol, and rat liver mitochondrial extract were in the range of 0.1 muM to 0.3 muM. This compared to values of apparent Km for DL-isocitrate for the same tissue preparations of 14 muM to 20 muM. One of the DL isomer pairs of alpha-methylisocitrate was inactive; the observations suggest that it is threo-alpha-methylisocitrate which inhibits TPN-linked isocitrate dehydrogenase. A method of synthesis of DL-threo-alpha-methylisocitric lactone (2-methyl-5-oxo-2,3-furandicarboxylic acid) from dimethyl trans-epoxymethylsuccinate and dimethylmalonate is described.