Comparative biochemical and immunological study of malic enzyme from two species of lactic acid bacteria: evolutionary implications.

Representatives of both Streptococcus faecalis and Lactobacillus casei produce isofunctional malic enzymes. All 10 strains of S. faecalis tested could be induced to synthesize malic enzyme and readily adapted to growth on malate. Although 17 of 21 L. casei strains could be induced to produce malic enzyme, only 9 of 14 strains tested grew at the expense of malate. A comparison of catalytic and regulatory properties suggested that the malic enzymes from S. faecalis and L. casei were very similar. Immunological analyses showed that the numerous similarities in function actually reflected partial protein homologies; however, two distinct forms of the malic enzyme were detected among different strains of L. casei by immunochemical and serological procedures. The division of L. casei into two subgroups based on the immunological type of malic enzyme synthesized corresponds to two subspecies currently recognized by microbial taxonomists.