Substrate Activity of Structural Analogs of Isocitrate for Isocitrate Dehydrogenases from Bovine Heart

Abstract

d-Garcinia acid (d-threo-1,2-dihydroxy-1.2.3-propanetricarboxylate), like d-threo-isocitrate, has an β-ds-hydroxyl group and a α-ls configuration of the second carboxyl group. The maximal velocity of pyridine nucleotide reduction with d-garcinia acid is 8 and 21% of d-threoisocitrate with the DPN-linked and TPN-linked isocitrate dehydrogenase from bovine heart, respectively. The other stereoisomers of hydroxycitrate [l-garcinia acid, d- and l-hibiscus acid (d- and l-erythro-1,2-dihydroxy-1,2,3-propanetricarboxylate)] are inactive. dl-threo-Homoisocitrate (dl-threo-1-hydroxy-1,2,4-butanetricarboxylate) supports DPN+ reduction at 10-15% of the rate observed for isocitrate with the DPN-specific enzyme, but is not a substrate for TPN-linked isocitrate dehydrogenase. The values of apparent So.5 for total isocitrate and total garcinia acid are similar with both enzymes; the apparent So.5 of total homoisocitrate is two- to threefold higher than that of total isocitrate with the DPN-linked enzyme. Enzymatic oxidative decarboxylation of garcinia acid and homoisocitrate leads to formation of α-keto-β-hydroxyglutarate and α-ketoadipate, respectively. dl-Methylmalate (dl-1-hydroxy-2-methylsuccinate) is inactive as a substrate for either dehydrogenase as are the newly synthesized compounds: dl-threo- γ-isocitric amide (dl-threo-1-hydroxy-3-carbamyl- 1,2-propanedicarboxylate), α-methyl-dl-isocitrate (dl-1-hydroxy-2-methyl-1,2,3-propanetricarboxylate),β-methyl- dl-garcinia acid (dl-threo-1-hydroxy-2-methoxy-1,2,3- propanetricarboxylate), dl-1-hydroxy-1,2,2-ethanetricarboxylate, and dl-1,4-dihydroxy- 1,2-butanedicarboxylate. © 1975, American Chemical Society. All rights reserved.