Regulation of carbohydrate composition of Saccharomyces cerevisiae under growth limitation.

Abstract

1. The carbohydrate composition of Saccharomyces cerevisiae cultivated aerobically in the chemostat at different growth rates was investigated. It was compared with the specific activities of enzymes of the reserve carbohydrate pathways. Under glucose limitation the synthesis of reserve carbohydrates increases strongly with increasing limitation of substrate supply, i.e., decreasing growth rate. Fermenting cells accumulate only glycogen, whereas more slowly growing organism with a purely oxidative metabolism contain trehalose and high amounts of glycogen. 2. During the budding process the purely respirative cells degrade part of their reserves. In the presence of excess substrate the reserve carbohydrate content is low and remains unchanged during the cell cycle. 3. The percentage of structural carbohydrates in the cells shows little changes during the budding cycle, being scarcely influence by the growth rate. 4. At a growth rate of 0.077 h-1 the cells cultivated under glucose limitation contain even a higher amount of reserves than those grown under nitrogen limitation. 5. The course of the specific activities of UDP-glucose pyrophosphorylase and glycogen phosphorylase as a function of the growth rate follows that of the reserve carbohydrates.