Membrane-bound L- and D-lactate dehydrogenase activities of a newly isolated Pseudomonas stutzeri strain

Pseudomonas stutzeri SDM was newly isolated from soil, and two stereospecific NAD-independent lactate dehydrogenase (iLDH) activities were detected in membrane of the cells cultured in a medium containing DL-lactate as the sole carbon source. Neither enzyme activities was constitutive, but both of them might be induced by either enantiomer of lactate. P. stutzeri SDM preferred to utilize lactate to growth, when both L-lactate and glucose were available, and the consumption of glucose was observed only after lactate had been exhausted. The Michaelis-Menten constant for L-lactate was higher than that for D-lactate. The L-iLDH activity was more stable at 55 degrees C, while the D-iLDH activity was lost. Both enzymes exhibited different solubilization with different detergents and different oxidation rates with different electron acceptors. Combining activity staining and previous proteomic analysis, the results suggest that there are two separate enzymes in P. stutzeri SDM, which play an important role in converting lactate to pyruvate.