Two Types of Soluble Malic Enzyme in Rat Tissues

Abstract

Malic enzyme [EC 1. 1. 1.40] was purified 270-fold to apparent homogeneity from the hepatic cytosol of rats fed on a high carbohydrate diet containing desiccated thyroid. On gel electrophoresis in the presence of sodium dodecyl sulfate, the purified enzyme was dissociated into a smaller unit of about one fourth the original size in accord with the ultracentrifugal results obtained with the alkaline degraded enzyme.
On Ouchterlony double diffusion tests, the rabbit antiserum prepared against the purified rat hepatic malic enzyme gave a single precipitin line with the purified enzyme, but two lines, major and minor, with crude hepatic extract. The main precipitin line was continuous with that of the purified enzyme and also with a single line formed by crude extract of adipose tissue reacting with the antibody. The minor line joined with a single precipitin line formed by crude heart extract and the antibody. These results imply that there are two immunologically different types of soluble malic enzyme in rat tissues, A (adipose tissue)-and H (heart)-types. Hepatic cytosol contained both types, and the amount of its A-type protein was apparently influenced by hormonal and nutritional stimuli.