Pyruvate oxidation in brain

Abstract

Cocarboxylase is essential for the decarboxylation by yeast of [alpha]-ketovaleric acid as well as of pyruvic and [alpha]-ketobutyric acids. Vit. B1 increases the rate of decarboxylation of [alpha]-ketobutyric and [alpha]-ketovaleric acids only in the presence of cocarboxylase; of [alpha]-ketovaleric acid slightly less than of the others. Pyruvic and [alpha]-ketobutyric acids are equally reactive with the pyruvate dehydrogenase system in minced pigeon brain under anaerobic conditions in the presence of methylene blue; [alpha]-ketovaleric acid is much less reactive. The Krebs'' dismutation proceeds to the same extent with [alpha]-ketobutyric acid and pyruvic acid; again [alpha]-ketovaleric acid is less affected. Washed brain tissue causes oxidative decarboxylation of [alpha]-ketobutyric acid, giving presumably propionic acid (next lower fatty acid); [alpha]-ketovaleric acid is oxidized to only a very slight extent. The purity of the acids used was important, high values for the R.Q. of [alpha]-ketobutyric acid being obtained in the presence of a slight impurity, [alpha]-Ketobutyric acid and [alpha]-ketovaleric acids enter into competitive inhibition with pyruvic acid both in the normal and avitaminous brains respiring in vitro. There is no inhibition of the indophenol oxidase system. Pyruvic and [alpha]-ketobutyric acids are oxidized at exactly the same rate under identical conditions. In the former case, however, most of the initial oxidation product undergoes complete combustion to CO2 and water. There is apparently an initial common path for oxidative decarboxylation; in the case of pyruvic acid a further system causes complete oxidation of part of the intermediate.