Regulation of Pyruvate Kinase by Fructose 1,6-diphosphate.

The concentrations of glycolysis intermediates, citric acid and adenine nucleotides were measured in resting cells of Saccharomyces cerevisiae during aerobic glucose metabolism. Addition of glucose resulted in a decrease in the intracellular content of phosphoglyceric acids and phosphoenolpyruvate. As extracellular glucose became depleted the level of these intermediates increased. Thus changes in theft intracellular content were regulated by factors other than the supply of extracellular substrate. Cross-over behaviour of phosphoenolpyruvate and pryruvic acid together with the inverse relationship which existed between the concentration of phosphoenolpyruvate and the rate of the pyruvate kinase reaction, indicated that regulatory changes in the activity of pyruvate kinase occurred. These activity changes were compared with those of the intracellular content of reposed in vitro effectors of the enzyme: fructose 1,6-diphosphate, citric acid, ATP and ADP. ATP and ADP did not appear to be involved in regulating changes in the activity of the enzyme. Although citric acid may have contributed towards some of the changes in enzyme activity, fructose 1,6-diphosphate appeared to be the primary relator, under the conditions of these experiments. Comparison of the results with the properties reported for the isolated enzyme, suggested that, in vivo, fructose 1,6-diphosphate affects the affinity of pyruvate kinase for phosphoenolpyruvate. This, in turn, appears to regulate the intracellular content of phosphoenolpyruvate and phosphoglyceric acids. The significance of the results is discussed in relation to both glycolysis and gluconeogenesis. [ABSTRACT FROM AUTHOR]