Studies on the aerobic degradation of glucose by Saccharomyces cerevisiae

Abstract

During the aerobic degradation of glucose by resting cells of Saccharomyces cerevisiae 80-90% of the carbon from positions 3 and 4 of glucose was converted into CO2, and almost all of the remaining carbon was found as ethanol at a time when O2 consumption had barely begun. It is concluded that the oxidation did not proceed by the hexose monophosphate pathway to any significant extent. As O2 uptake continued, ethanol disappeared and acetate accumulated. (With cells grown in a synthetic medium, material of the oxidation level of acetaldehyde also appeared as an intermediate in glucose degradation). The further oxidation of these C2 compounds was inhibited by fluoroacetate, which suggests participation of the tricarboxylic acid cycle. This contention is confirmed by the finding that, when labeled glucose was oxidized, the specific activity of the CO2 produced from C-1, C-2, C-5 and C-6 was comparable with that of cycle acids isolated from the cells. The oxidation of accumulated acetate is adaptive in nature; its rate increased during glucose degradation. Arsenate inhibited the oxidation of glucose to CO2, presumably by preventing adaptation to acetate oxidation.