Decarboxylation by intact yeast and pyruvate decarboxylase of some derivatives of pyruvic acid and alpha-ketoglutaric acid.

Abstract

1. It has been confirmed that under anaerobic conditions at pH 2 pyruvic acid is vigorously decarboxylated by intact baker's yeast, but hardly at all at pH 5.5. Furthermore, the decarboxylation occurs more slowly with semiaerobically cultured than with aerobically cultured baker's yeast. 2. The penetration of pyruvic acid ethyl ester into the cell is not dependent upon the pH of the medium. The ester is decarboxylated by intact yeast at about the same rate, at pH 2 and 5.5. It is not decarboxylated by a purified preparation of pyruvate decarboxylase (EC 4.1.1.1). 3. Hydroxypyruvic acid is decarboxylated only slowly by intact yeast at pH 2 and pyruvate decarboxylase. The attachment of a phenyl group to the pyruvic acid molecule increase the permeability, but causes an inhibition of pyruvate decarboxylase. 4. α-Ketoglutaric acid is decarboxylated neither by intact yeast nor by an enzyme preparation, but with disintegrated yeast a noticeable formation of CO2 is observable. By intact yeast, the γ-ethyl ester of α-ketoglutaric acid reacts towards the acidity of the medium in the same way as does pyruvic acid. With purified pyruvate decarboxylase, the ester is decarboxylated more slowly than α-ketovaleric acid, but more rapidly than α-ketocaproic acid. Nevertheless, it does not penetrate into the intact yeast cell at a weak concentration to the same extent as do the acids last mentioned. α-Ketoglutaric acid diethyl ester behaves in a similar way to pyruvic acid ethyl ester: it penetrates the plasma membrane, and is decarboxylated by yeast but not by a preparation of pyruvate decarboxylase.