Printed in U.S.A. Purification and Properties of Lactobacillus plantarum Inducible Malic Enzyme

Inducible malic enzyme (L-malate:NAD oxidoreductase [decarboxylating], EC 1.1.1.39) was isolated from Lactobacillus plantarum and purified about 100-fold with 27 % yield of the original activity. Kinetic studies with the purified malic enzyme yielded the following results: pH optimum, 7.6 to 8.0; Km for L-malate, 0.38 mM; Km for NAD, 0.072 mM; and Km for MnCl2, 0.048 mM. It was shown that this enzyme was inhibited by high concentrations of substrate and nicotinamide adenine dinucleotide (NAD), indicating it may be regulated by substrate or NAD. Molecular weight of 130,000 10,000 was determined by Sephadex gel filtration and sodium dodecyl sulfate-polyacrylamide gel electro-phoresis. The isoelectric point, determined by isoelectrofocusing, was 4.3 at 7 C. Isoelectrofocusing also resolved three active peaks which focused at pH 4.19, 4.31, and 4.40. Inducible, nicotinamide adenine dinucleotide (NAD)-dependent, malic enzymes which cata-lyze the oxidative decarboxylation of L-malic acid to pyruvic acid and carbon dioxide are found in many lactic acid bacteria (2, 11, 20, 25) and yeast (36). Other microbial, as well as plant and animal malic enzymes, are constitutive and utilize NAD phosphate (NADP) as coenzyme. Escherichia coli is unusual in that it has two constitutive malic enzymes: one, NAD-depend-ent, and the other, NADP-dependent (8). Sev-eral microbial malic enzymes have been iso