Abstract
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.
Highlights
The kinetics of induced synthesis of glycolytic enzymes of parent lack of interest in glycolytic enzyme induction is the sothe hybrid yeast Saccharomyces fragilis X Saccharomyces called constitutive nature of such enzymes
Coordinate Synthesis of Glycolytic EnzymesGrowth of the hybrid yeast S. fragilis x S. dobzhanskii in the presence of glucose in either salt-vitamin medium or in yeast extract-peptone was accompanied by increased levels of all glycolytic enzymes except alcohol dehydrogenase and aldehyde dehydrogenase
The results show that the two major bands of hexokinase, in the order of their increasing mobility, were in the proportion of 9 and 8 milliunits in the uninduced extract (A) and 44 and 39 milliunits in the extract from the culture induced with glucose (B)
Summary
Growthof Yeast-A hybrid strain of Saccharomycejrsagilis x Saccharomycedsobzhunskiig, iven to us by Dr H. 0. Growthof Yeast-A hybrid strain of Saccharomycejrsagilis x Saccharomycedsobzhunskiig, iven to us by Dr H. In mostof the experiments,,weusedthe hybrid yeast, inasmuchasthe ratio of glycolytic enzyme activity of culturesgrown in the presence of glucoseto that in its absenceis much higher for this yeast than for the other two. Cultures were grown overnight in a basal medium containing peptone (1 g/100 ml), yeast extract (0.3g/100 ml), andsodiumacetate (50mu) at 30” with shaking. The culture was resuspendedin fresh medium and, when ex-. The regulation of glucoseutilization is one of the ponentialgrowth wasachieved,the appropriatesugarwasadded earliest describedphenomenain cellular control systems,very and the culture was allowed to grow. Little is known about the control of synthesisof glycolytic en- each flask was removed and chilled, the yeast was washedby zymes. Containing mu 2-mercaptoethanoal nd 2 mu EDTA in 50 mu Kinetics of Glycolytic Enzyme Xynthesis Perhaps,is our lack of under- centrifugation oncein 150mu cold KC1 and in a medium standing of the genetic determinantsof the glycolytic system. containing mu 2-mercaptoethanoal nd 2 mu EDTA in 50 mu Kinetics of Glycolytic Enzyme Xynthesis
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