QUANTITATIVE ASPECTS OF THE TRICARBOXYLIC ACID CYCLE IN BAKER'S YEAST

Abstract

A suspension of baker''s yeast was permitted to oxidize acetate-2-C14 in the absence of additional substrates. The cells were separated into several fractions and the compounds containing C14 were isolated from each fraction by chromatographic procedures. All of the isotope was located in acetate, citrate, [alpha]-ketoglutarate, succinate, fumarate, malate, glutamate, aspartate, alanine and glycine. The citrate, [alpha]-ketoglutarate, succinate, fumarate and malate were highly labeled and in isotopic equilibrium with each other. Similarly the glutamate was in isotopic equilibrium with the [alpha]-ketoglutarate. The specific activities of the remaining amino acids were variable and consistently less than those of the intermediates of the tricarboxylic acid cycle. The distribution of C14 found in citrate and succinate, coupled with the other isotope data, are presented as evidence that the tricarboxylic acid cycle is a major pathway of acetate oxidation by non-proliferating suspensions of baker''s yeast.