Metabolism of D- and L-Lactate by Pseudomonas putida

Abstract

Pseudomonas putida grew at the same rate with the same molar growth yield on D-, L, or DL-Iactate as the sole source of carbon for growth. D- and L- lactate were utilized simultaneously and at the same rate when the organism was grown on DL-Iactate (ratio of D isomer to L isomer of 1: 1). Growth on either isomer alone, or in combination, caused the induction of both a D-lactate, and an L-Iactate dehydrogenase. Both enzymes were particulate and used dichlorophenolindophenol, or oxygen, but not NAD, as electron acceptor, and were inhibited by cyanide when oxygen was the electron acceptor. The pH optimum for the D-lactate dehydrogenase was about 6·5, and for the L-Iactate dehydrogenase was about 8· O. The D-lactate dehydrogenase was more heat-sensitive than the L-Iactate dehydrogenase. The stoichiometry of both enzyme reactions was the same with 2 mol of lactate being oxidized by 1 mol of oxygen to form 2 mol of pyruvate. No lactate racemase was detected in the cell extracts.