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Influence of Carboxylic Acids on the Stereospecific Nicotinamide Adenine Dinucleotide-Dependent and Nicotinamide Adenine Dinucleotide-Independent Lactate Dehydrogenases of Leuconostoc mesenteroides

^a Institut für Mikrobiologie und Weinforschung der Johannes Gutenberg-Universität, Mainz, Germany

ABSTRACT

Leuconostoc mesenteroides increased its lactic acid production from glucose threefold when malic acid was added to the culture. This increase resulted also in a reduction of the ratio of D-lactic acid to L-lactic acid (31.5 to 1.23). Addition of malic acid increased 6.5-fold the specific activity of nicotinamide adenine dinucleotide (NAD)-linked L-lactate dehydrogenase and increased 3.2-fold that of NAD-linked D-lactate dehydrogenase. The Michaelis constant (K_m) for NAD of the NAD-linked L-lactate dehydrogenase increased with the addition of malate, but no change was observed in the K_m values for the respective D-enzyme. The effect of carboxylic acids on the NAD-linked L-lactate dehydrogenase activities was tested by using partially purified enzyme preparations from cells grown with glucose alone and from cells grown with glucose plus malate. Malate stimulated the L-enzyme and inhibited the D-lactate dehydrogenase. The NAD-linked L-lactate dehydrogenase exhibited the same activity bands on polyacrylamide gel electrophoresis whether the cell-free preparation originated from cells grown on glucose plus malate or on glucose as the sole carbon source. The NAD-linked D-lactate dehydrogenase, however, exhibited a different pattern of electrophoretic mobility, depending upon the source of origin of the cell-free preparation. The results suggest that malate has a stimulatory effect on the synthesis of both enzymes and may result in rearrangement of the protein structure of the D-lactate dehydrogenase. This rearrangement apparently makes the D-enzyme more susceptible to inhibition of catalytic activity. The L-lactate dehydrogenase, however, is stimulated not only in its synthesis but also in its activity. It is proposed that these effects are responsible for the regulation of lactic acid production.

¹ Present address: Department of Microbiology, University of Queensland, Medical School, Herston, Brisbane, Queensland 4006, Australia.