A study of NADP+- linked isocitrate dehydrogenase from germinating mung bean (Vigna radiata)

Abstract

NADP+- linked isocitrate dehydrogenase has been purified to apparent homogeneity from 36 h germinated mung beans by ammonium sulphate fractionation, heat treatment, acid treatment, and DEAE - Cellulose column chromatography. The enzyme was purified to 150 fold with 15% recovery. The preparation showed single protein band on native PAGE and was free from bound nucleotides and coloured pigments (A280/A260 = 1.4). The molecular weight was found to be 141,000 and was made of four identical subunits (mol wt 36,000). Thermal inactivation at 50, 53, and 55°C revealed simple first order kinetics and t1/2 was found to be 38, 10, and 3 min, respectively. The enzyme exhibited absolute specificity for NADP+ and substrate. The Km for isocitrate and NADP+ was 28.57 μM and 70 μM, respectively. The enzyme appeared to be regulated by various metabolites of Krebs' cycle intermediates.