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

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 t_1/2 was found to be 38, 10, and 3 min, respectively. The enzyme exhibited absolute specificity for NADP⁺ and substrate. The K_m 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.