Crystallization and some properties of D-lactate dehydrogenase from Staphylococcus sp LDH-1

Staphylococcus sp. LDH-1 isolated as a high producer of lactate dehydrogenase grew well under anaerobic conditions and produced a large amount of D-lactate dehydrogenase (D-LDH), but not L-LDH. After purification of this D-LDH, some properties were revealed. The enzyme catalyzed the reversible reduction of 2-oxo acids into D-2-hydroxy acids, but not into L-2-hydroxy acids. The Km values for 2-oxo acids were much smaller than those for D-2-hydroxy acids, and the V-max values for 2-oxo acids were much greater than those for D-2-hydroxy acids. The equilibrium constants for the reaction of the reductions of pyruvic acid to D-lactic acid and of 2-oxobutyric acid to D-2-hydroxy-n-butyric acid were 270 and 360, respectively. The enzyme was stable between pH 5.5 and 8.5, while the optimum pH for pyruvic acid and D-lactic acid was pH 5.0 and 8.2, respectively. It was therefore concluded that the D-LDH from Staphylococcus sp. LDH-1 is available as enzyme for an assay of pyruvic acid and for the production of D-2-hydroxy acids.