Properties of D-lactate dehydrogenase from Lactobacillus bulgaricus: a possible different evolutionary origin for the...

The NAD-dependent D-lactate dehydrogenase from Lactobacillus bulgaricus has been purified to homogeneity. This enzyme was a dimer made of two identical chains of molecular mass 37,000. Saturation by either substrate was hyperbolic, with Km values of 50 microM for NADH and 1 mM for pyruvate. The specific activity was 2200 units/mg and was not affected by the presence of fructose-1,6-bisphosphate, Mn2+ ions, ATP or ADP. The amino-terminal sequence determined on 50 residues showed no significant homology with known lactate dehydrogenases, suggesting that the D-lactate dehydrogenase from L. bulgaricus could not be evolutionarily related to the family of NAD-dependent L-lactate dehydrogenases.