D-Lactate dehydrogenase of Peptostreptococcus elsdenii

D-Lactate dehydrogenase has been purified to near homogeneity from Peptostreptococcus elsdenii. As isolated, the enzyme contains flavine adenine dinucleotide and a tightly bound metal cofactor. Inactivation by ortho-phenanthroline occurs in two steps and is partially blocked by D-lactate. Reactivation by divalent metal ions occurs, with divalent zinc being the most effective. When ferricyanide is used as the electron acceptor, D-lactate has an apparent K0.5 of 3.3 M0.46; its binding is negatively cooperative with a Hill coefficient of 0.46. Replacement of ferricyanide by the other components of the electron transport system yields hyperbolic kinetics with an apparent Km for D-lactate of 26 mM. The apparent Km for ferricyanide is 2.2 X 10(-4) M. Phosphate and pyrophosphate compounds stimulate the D-lactate:ferricyanide activity. These properties suggest that interaction of this enzyme with other electron transport proteins in the chain may enhance D-lactate binding and, hence, the rate of electron transport.