REGULATION OF THE "MALIC" ENZYME IN NEUROSPORA CRASSA

Abstract

"Malic" enzyme has been isolated from Neurospora crassa which can bring about the reversible carboxylation of pyruvic acid. The enzyme is specific to L-malate and NADP and is activated by Mn⁺⁺ and Mg⁺⁺. The partially purified enzyme does not decarboxylate oxaloacetate but is competitively inhibited by it. This enzyme is synthesized only during the early stages of the growth cycle and is repressed by acetate. In addition, the oxidative decarboxylation of malic acid is competitively inhibited by aspartic acid; the degree of inhibition depends upon the cell growth phase from which the enzyme is extracted. "Malic" enzyme isolated from a 12-h culture is not significantly inhibited by aspartate. However, this inhibition increases to 90% if an enzyme preparation from a 24-h culture is used. The significance of enzyme repression by acetate and the inhibition of the activity by aspartate are discussed.