title: Steady-state kinetic studies on D-lactate dehydrogenase from Megasphera elsdenii.
abstract: Initial rate measurements were made of the oxidation of D-lactate and D-alpha-hydroxybutyrate by oxygen and potassium ferricyanide, catalyzed by D-lactate dehydrogenase from Megasphera elsdenii. The detailed kinetic work indicates a "ternary complex" type mechanism, with a complex of keto acid and reduced enzyme reacting with the electron acceptor at pH 8. However, as the pH is lowered, the double-reciprocal plots become nonlinear, with a downward curvature. This seems to be due to negative interactions within the protein rather than to a complexity of the kinetic mechanism. The variation of initial rate parameters at pH 8 with temperature yields nonlinear Arrhenius plots with a greater activation energy above the break point than below. This type of behavior has been previously reported only for fumarase (Massey, 1953). Studies with deuterated D-lactate show only a small isotope effect on phi 0 and phi 1 (KM/Vmax for lactate) but a large effect on phi 2 (Km/Vmax for ferricyanide).
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002384:Catalysis; D005292:Ferricyanides; D005420:Flavoproteins / Q000378:metabolism; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen; D013696:Temperature; D045854:Veillonellaceae / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D005292:Ferricyanides; D005420:Flavoproteins; D007770:L-Lactate Dehydrogenase; D010100:Oxygen