The dissimilation of the carbohydrate reserves of a strain of Saccharomyces cerevisiae

Abstract

When a brewing strain of S. cerevisiae was grown under substantially anaerobic conditions the carbohydrate reserves, glycogen and trehalose, made up 40% of the cell dry weight. Contact with oxygen initiated alcoholic fermentation of these carbohydrate reserves. The fermentation continued at a faster rate under aerobic than anaerobic conditions. A complete cytochrome system was not necessary for this effect of oxygen since it occurred in a respiration-deficient mutant. The yeast fermented glucose at the same rate under both aerobic and anaerobic conditions. In aerobically grown yeast, the carbohydrate reserves made up less than 10% of the yeast dry weight. The trehalose fraction was very small. Measurement of the endogenous gaseous exchanges indicated that there was very little utilization of the reserve carbohydrate in the yeast grown in this way. The yeast reserves provided a sufficient energy source for the synthesis of respiratory enzymes during the aeration of anaerobically grown resting cells. Evidence is presented which indicates that part of the degradation products of the yeast carbohydrate was oxidized and the rest used for the synthesis of long-term reserves.