NADP-Specific Isocitrate Dehydrogenase of Mycobacterium phlei ATCC 354: Purification and Characterization

SUMMARY: NADP-dependent isocitrate dehydrogenase (EC 1.1.1.42) from Mycobacterium phlei ATCC 354 was purified to homogeneity by ammonium sulphate fractionation, followed by DEAE cellulose and Sephadex G-200 chromatography. The pH optimum of the enzyme was 8·5. The K m values for isocitrate and NADP were 74 and 53 μm, respectively. Mn2+ was essential for enzyme activity. The enzyme lost all activity on incubation at 70°C for 15 min; isocitrate and NADP protected against this thermal inactivation. p-Chloromercuribenzoate inhibited the enzyme; pre-incubation of enzyme with isocitrate + Mn2+ prevented this inhibition. The purified enzyme showed concerted inhibition by glyoxylate + oxaloacetate and was inhibited by oxalomalate.