Isolation and Characterization of NADP⁺-Specific Isocitrate Dehydrogenase from the Pupa of Bombyx mori

Abstract

NADP⁺-specific isocitrate dehydrogenase was found in several tissues of the pupa of the silkworm, Bombyx mori. This enzyme was highly purified from the whole bodies of pupae. This is the first isolation of the enzyme from insect materials. The purified enzyme gave a single protein band on polyacrylamide gel electrophoresis. The reaction catalyzed by the purified enzyme was readily reversible. The pH optimum for the forward reaction (reduction of NADP⁺) was 7.8, and that for the reverse reaction (oxidation of NADPH) was 6.6. The enzyme had a molecular weight of 86, 000 and was found to be composed of two identical subunits, which have a molecular weight of 44, 000. The activity of the enzyme in the forward reaction was slightly inhibited by citrate, oxaloacetate, α -ketoglutarate, and others. Citrate stabilized the activity over a wide pH region.