[Characteristics of lactate dehydrogenase isoenzymes of loach differentiated tissues and eggs]

The degree of inhibition by pyruvate, oxalate and urea was determined for the lactate dehydrogenase (EC 1.1.1.27) of some tissues of adult loach (Misgurnus fossilis) and for the lactate dehydrogenase isozymes, which were resistant to the inhibition by AgNO3 and dominated by their activity in the unfertilized eggs of the investigated species. It was found that the skeletal muscle lactate dehydrogenase was not sensitive to the pyruvate excess, but was inhibited by high concentrations of urea and in lower degree by oxalate. The heart muscle lactate dehydrogenase was inhibited by the substrate but only at high concentrations of the last. The main part of the eggs' lactate dehydrogenase was not sensitive to the urea, but it was very sensitive to oxalate and pyruvate. The liver lactate dehydrogenase was inhibited by urea and oxalate in the higher degree than the skeletal muscle enzyme, but after the heat inactivation of the main liver-specific isozyme the differences between them became insignificant. The skeletal muscle lactate dehydrogenase had the lower pH optima than the investigated group of the eggs isozymes. The subunit structure of the lactate dehydrogenase isozymes of different loach tissues and eggs is discussed.