Structure and function of L-lactate dehydrogenases from thermophilic and mesophilic bacteria, IV. The primary structure of the mesophilic lactate dehydrogenase from Bacillus subtilis.

The complete amino-acid sequence of lactate dehydrogenase from the mesophilic Bacillus subtilis (B. X1) was determined. Approximately 70% of the sequence was obtained by sequence analysis of intact protein (N-terminal sequence) and of four CNBr fragments (CNBr3, CNBr4, CNBr5 and CNBr6). Sequences overlapping the CNBr fragments were determined from polypeptide fragments obtained by cleavage using o-iodosobenzoic acid (cleavage at Trp) or clostripain (cleavage at Arg). The C-terminal amino-acid residue (Asn) was detected by carboxypeptidase Y-degradation. Lactate dehydrogenase from B. subtilis shows a 69% sequence homology to that from the thermophilic strain B. stearothermophilus, and a 34% sequence homology to those from higher organism. The homology of these enzymes is particularly high at the active site regions (the coenzyme and substrate binding sites). The relatively high sequence conservation of the lactate dehydrogenases from B. subtilis and B. stearothermophilus (and from other bacilli) allows a structural comparison of this temperature variants.