The malic dehydrogenase of animal tissues

Publisher Website
Google Scholar
Abstract
The preparation of a highly active malic dehydrogenase from the heart muscle of the pig is described. The product of oxidation, oxaloacetic acid, completely inhibited the oxidation even in extremely small concn. The use of ketone fixatives such as cyanide hydrazine, semicarbazide and hydroxylamine was essential in order to obtain a linear rate of oxidation. The catalytic system comprised the dehydrogenase, co-enzyme I, carrier and malate. Methylene blue, pyo-cyanine, lactoflavin and adrenaline were the most active carriers; flavoprotein was only slightly active; cytochrome and glutathione were inactive. The enzyme system specifically oxidized l ([long dash]) malic acid to oxaloacetic acid[long dash]the latter being isolated as the 2: 4-dinitrophenyl-hydrazone. The so-called fumaric dehydrogenase proved to be merely malic dehydrogenase collaborating with fumarase. The malic enzyme was not identical with the lactic enzyme. Fumaric acid had been shown to dismute anaerobically to form succinic and oxaloacetic acids. The dismutation depended upon the presence of the succinic and malic enzymes, coenzyme I and a suitable carrier. The malic dehydrogenase was found in high concn. in the tissues of the rat, rabbit and pigeon.