Purification of several NADP-dependent malate dehydrogenase isozymes from spinach leaves. Kinetic properties

Four NADP-malate dehydrogenase (NADP-MDH) (EC 1.1.1.82) isozymes from spinach leaves have been purified to apparent homogeneity by DEAE-cellulose and affinity chromatography, and molecular sieving. They have the same native molecular weight (≈57 000) as determined by sedimentation equilibration analysis. They can be distinguished by their eletrocphoretic and chromatographic (over DEAE-cellulose) behaviors. On this basis, they constitute two sets of two enzymes each: MDH-A and -B, and MDH-C and -D. Catalytic properties of the most abundant isozyme, MDH-A, have been studied. Both NADPH and oxaloacetate inhibit the forward reductive reaction. Other kinetic parameters are also presented.