A kinetic study of glycolytic enzyme synthesis in yeast

Abstract

The kinetics of induced synthesis of glycolytic enzymes of the hybrid yeast Saccharomyces fragilis x Saccharomyces dobzhanskii in response to the addition of glucose or galactose has been studied in a basal medium containing peptone, acetate, and yeast extract. Glucose and galactose bring about a 3- to 100-fold increase in specific activity of various glycolytic enzymes during a 7- hour period. The smallest increase is observed in the case of P-glucoisomerase (EC 5.3.1.9) and the largest with glyceraldehyde-3-P dehydrogenase (EC 1.2.1.12). In the stationary state of cells grown in the presence or absence of glucose, the glycolytic enzymes display a coordinate relationship to one another. The time course of enzyme synthesis by glucose and galactose, as well as of enzyme disappearance on removal of the sugars, however, suggests a kinetic heterogeneity. With galactose as the inducing carbohydrate, the enzymes increase in specific activity in the following sequence: pyruvate kinase (EC 2.7.1.40), within 20 min after addition of galactose; P-glucomutase (EC 2.7.5.1), P-fructokinase (EC 2.7.1.11), and glyceraldehyde-3-P dehydrogenase, within 1 hour; P-glucoisomerase, P-glycerate kinase (EC 2.7.2.3), P-glycerate mutase (EC 2.7.5.3), and enolase (EC 4.2.1.11), between 1 and 3 hours; hexokinase (EC 2.7.1.1), aldolase (EC 4.1.2.7), triose-P isomerase (EC 5.3.1.1), and pyruvate decarboxylase (EC 4.1.1.1), between 2 and 5 hours. Alcohol dehydrogenase (EC 1.1.1.1) falls outside any of these groups; after an initial period of repression, galactose causes increased synthesis of this enzyme during later periods. The increase of glycolytic enzyme activity elicited by sugars seems to be due to increased production of the same enzyme species already existing in uninduced cultures. The glucose-induced increase in glycolytic enzyme activity in Saccharomyces cerevisiae is completely prevented by cycloheximide, an inhibitor of protein synthesis in this yeast. P-Fructokinase and pyruvate decarboxylase decay rapidly inside the cells in the presence of this antibiotic.