Über die katheptische Inaktivierung einiger Enzyme der Rattenleber, insbesondere der Glucokinase

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Abstract
The enzymes glucokinase, pyruvate kinase and fructose diphosphate aldolase, in the 100,000 x g supernatant of a rat liver homogenate, are inactivated by a lysosomal cathep-sin. This phenomenon was further investigated with a partly purified glucokinase preparation. The inactivation is more rapid at a weakly acid pH than at pH 7; it is accelerated by [beta]-mercaptoethanol, and it is inhibited by the substrates of glucokinase (glucose and ATP) and by potassium and ammonium ions. The fractionation of a lysosome extract on Sephadex G-100 gave 2 maxima for cathepsin B, of which the smaller was identical with the enzyme- inactivating activity and showed a molecular weight of 25,000. In the lysosome extract, the enzyme only slowly decreases in activity during storage for several months at 0[degree]C, while the passage through Sephadex causes considerable loss of activity. Only the liver-hexokinases and pyruvate kinases are in-activated; the corresponding enzymes from muscle are not affected. Since the 2 liver enzymes are key enzymes of glycolysis, their catheptic inactivation together with their dependence on diet and insulin can be seen to constitute a regulation system. Both the muscle and liver forms of fructose diphosphate aldolase, however, are partly inactivated. So far 10 other enzymes of glycolysis and transamination have been studied, and none is inhibited by cathepsin. It was not possible to identify the enzyme-inactivating activity with certainty with any known cathepsin.