The lactic dehydrogenase of animal tissues

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Abstract
The lactic dehydrogenase system of animal tissues is made up of the following components: enzyme, coenzyme, lactate and carrier. The product of oxidation[long dash]pyruvic acid[long dash]inhibits almost completely the oxidation of lactic acid. Ketone-fixing agents, such as cyanide and hydroxylamine, combine with pyruvic acid and allow the oxidation of lactic acid to proceed linearly for a time. The effects of pH and of concn. of coenzyme and substrate on the rate of oxidation were studied. The lactic enzyme was found associated with the enzymes for the oxidation of malate, fumarate, [beta]-hydroxypropionate and [beta]-hydroxy-butyrate. Methods of separating partially the lactic enzyme from the others are descr. The lactic enzyme catalyzes the oxidation of I ( +) -lactate to pyruvic acid which can be isolated as the 2.4-dinitrophenylhydrazine derivative. d([long dash])-lactate, lactamide and isoserine are not oxidized. Among the natural carriers, flavin, adrenaline and to a slight extent yellow pigment (flavoprotein or yellow enzyme) function as carriers for the reaction with O; cytochrome, ascorbic acid and glutathione are inactive. The lactic coenzyme can be reduced with hydrosulphite or by the enzyme system. Reduced coenzyme reduces flavin, methylene blue, yellow pigment and the red substance formed from adrenaline; it does not reduce cytochrome. Reduced coenzyme is unstable in acid soln. but not in alkaline. The Warburg scheme of coenzyme action is found to apply to the lactic system. The coenzyme functions as a highly specific carrier betwen lactic acid and the O transporter. The coenzyme of the hexosemonophosphate dehydrogenase cannot replace the lactic coenzyme in the lactic system. The enzyme preparation may be purified extensively by treatment with kieselguhr and kaolin. Water-clear solns. can be prepared with Qo2 values from 400 to 500. The lactic enzyme is widely distributed in animal tissues. Its quantitative estimation was carried out in the tissues of pigeon, rabbit and rat. A new classification of dehydrogenase systems is presented based on recent research.