Nicotinamide Adenine Dinucleotide-specific Glyceraldehyde 3-Phosphate Dehydrogenase from Pisum sativum

NAD+-specific glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.12) was purified from pea seeds to a specific activity in excess of 200 units per mg of protein, with a recovery of one-third of the initial activity. The specific activity is similar to that of the pure enzyme from other sources. On the basis of sedimentation velocity and sodium dodecyl sulfate gel electrophoresis studies, the enzyme appears to be homogenous. It is a tetramer, with a subunit molecular weight of approximately 36,000 to 37,000. Each subunit has the capacity to bind 1 mole of NAD+, and the enzyme, as isolated, contains 2 to 3 moles of NAD+ per tetramer. The amino acid composition is similar to that of the enzyme from other sources. The enzyme has a pH optimum between 8.5 and 9.0. Each of the substrates, but particularly glyceraldehyde 3-phosphate, is inhibitory at high concentrations. In all major respects, the pea seed enzyme does not appear to differ markedly from glyceraldehyde 3-phosphate dehydrogenase from other sources.