Membrane transport as controlling pacemaker of glycolysis in Saccharomyces carlsbergensis

Abstract

The frequency of anaerobic NADH oscillations in Saccharomyces carlsbergensis following addition of fructose is 1.5–2.0 times slower than that following addition of glucose. Since catabolism of the two sugars differs in the sugar phosphorylation pathway only, the reason for the observed alternation of the frequency must be sought among these reactions. It has been found that: 1. 1. The equilibrium of hexose phosphates, as catalized by phosphoglucose isomerase, is nearly independent of the added hexose. 2. 2. The yield of ethanol, the end product of anaerobic glycolysis in yeast, depends on the rate of sugar consumption rather than on the kind of assimilated sugar. 3. 3. The two hexoses stimulate equally the utilisation of storage material. 4. 4. The half-saturation constant of fructose consumption is 10 times higher than that of glucose consumption. 5. 5. Intracellular fructose concentration may reach a level 10 times higher than that of glucose. 6. 6. Analysis of the kinetic data points to membrane transport as the rate limiting step of glycolytic flux. Application of the crossover theorem showed that the passage of sugar molecules across the cell membrane is affected by regulatory alterations of the flux as well. Glucose 6-phosphate is discussed as a possible feed-back inhibitor of membrane transport.