Effects of Glucose Repression and Anaerobiosis on the Activities and Subcellular Distribution of Tricarboxylic Acid Cycle and Associated Enzymes in Saccharomyces carlsbergensis

Abstract

Cell-free extracts were prepared from sphaeroplasts of aerobically and anaerobically grown, glucose-derepressed and glucose-repressed Saccharomyces carlsbergensis. The activities of the enzymes of the tricarboxylic acid cycle and of related enzymes were measured, together with their distributions after differential centrifugation. Glucose repression lowered activities of enzymes of the tricarboxylic acid cycle by 60 to 89 % under aerobic conditions. Activities were still further decreased under anaerobic glucose-derepressed conditions. 2-Oxoglutarate decarboxylase activity was not detected after anaerobic growth; malate synthase and isocitrate lyase activities were not detected in organisms grown either aerobically or anaerobically. Glucose had little effect on the activities of tricarboxylic acid cycle enzymes under anaerobic conditions, with the exception of citrate synthase whose activity increased under anaerobic glucose-repressed conditions. Differential centrifugation of cell-free extracts showed different distribution patterns of the enzymes under the four growth conditions. The distribution patterns and enzyme activities reflected the differential effects of glucose repression and/or anaerobiosis.