The regulation of lactate dehydrogenase activity in soy-bean seedlings

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Abstract
An electrophoretically homogeneous lactate dehydrogenase was isolated from soybean seedlings, the specific activity of which was approximately 1800 times higher than the crude extract. From the dependence of the rate of reaction catalyzed by lactate dehydrogenase on substrate concentration, Michaelis constants and Hill coefficients were determined for four natural substrates,i.e. lactate, pyruvate, NAD and NADH. The enzyme from soy-bean plants is non-competitively inhibited by oxalate and mesoxalate,i.e. by the compounds analogous to the substrate. At pyruvate concentrations above 0.8 mM, the rate of reaction catalyzed by lactate dehydrogenase from soy-bean plants decreases, fructose diphosphate and ATP function as inhibitors as well. The inhibition by ATP is pH dependent, which seems to be of importance for the regulation of enzyme activityin vivo.