A comparative study of malolactic enzyme and malic enzyme of different lactic acid bacteria

Abstract

Malolactic enzyme of lactic acid bacteria catalyzes the decarboxylation of L-malate to L-lactate. The appropriate enzyme of Lactobacillus casei, Leuconostoc oenos, and Leuconostoc mesenteroides, as well as the malic enzyme of Lactobacillus casei, were purified to electrophoretic homogeneity by salmine sulphate precipitation, ion-exchange chromatography, hydrophobic chromatography, and gel filtration. The malolactic enzymes investigated were similar and showed only minor variations in the isoelectric point and the temperature optimum. The molecular weight of the subunit of all malolactic enzymes was about 65 000. Aggregates were formed, depending on the pH. The optimum activity of malolactic enzyme was observed at pH 5.8–6.0, and at this pH the dimer was stable. In addition to Mn2+ and NAD, the malolactic enzyme required K+, which was replaceable by NH4+, for maximum activity. The Km values for L-malate were 10.9 mM (Leuconostoc mesenteroides B116) and 3 mM (Leuconostoc oenos). The Km values for Mn2+ were 0.1 mM (Leuconostoc mesenteroides B116) and 0.017 mM (Leoconostoc oenos). Malic enzyme oxidatively decarboxylates L-malate to pyruvate. This enzyme consists of a 37 000 subunit that forms dimers and tetramers. The NAD-dependent malic enzyme of Lactobacillus casei decarboxylates oxalacetate and is therefore regarded as a L-malate:NAD+ oxidoreductase (oxalacetate decarboxylating), EC 1.1.1.38. Key words: malolactic enzyme, malic enzyme, Lactobacillus, Leuconostoc.