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

AUTOR(ES)

Doelle, Horst W.

RESUMO

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 (Km) for NAD of the NAD-linked l-lactate dehydrogenase increased with the addition of malate, but no change was observed in the Km 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.

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