Phosphoglycerate dehydrogenase from soybean nodules : partial purification and some kinetic properties

Phosphoglycerate dehydrogenase (EC 1.1.1.95), an enzyme believed to be involved in the synthesis of serine, an intermediate in ureide biosynthesis, has been purified about 200-fold from nodules of soybean (Glycine max L. Merr. cv Amsoy 71). The reaction was reversible and exhibited a strong pH dependence with optima of 9.4 and 6.1 for the forward and reverse reactions. The K(m) values for the forward reaction were 0.25 millimolar for NAD(+) and 0.29 millimolar for d-3-phosphoglycerate at pH 9.4, while those for the reverse reaction were 12 mum for NADH and 0.15 millimolar for 3-phosphohydroxypyruvate at pH 7.5. NADPH functioned as an alternate reductant with a K(m) of 0.15 millimolar. Product inhibition for the reverse reaction was competitive for NAD(+) with respect to NADH and noncompetitive for phosphoglycerate with respect to phosphohydroxypyruvate. Phosphoglycerate dehydrogenase activity was dependent on inorganic ions and was not inhibited by serine.