Purification and Characterization of Cytosolic NADP Specific Isocitrate Dehydrogenase from Pisum sativum.

Cytosolic NADP-specific isocitrate dehydrogenase was isolated from leaves of Pisum sativum. The purified enzyme was obtained by ammonium sulfate fractionation, ion exchange, affinity, and gel filtration chromatography. The purification procedure yields greater than 50% of the total enzyme activity originally present in the crude extract. The enzyme has a native molecular weight of 90 kilodaltons and is resolved into two catalytically active bands by isoelectric focusing. Purified NADP-isocitrate dehydrogenase exhibited K(m) values of 23 micromolar for dl-isocitrate and 10 micromolar for NADP, and displayed optimum activity at pH 8.5 with both Mg(2+) and Mn(2+).