Effect of Caffeine on Glucose‐Induced Inactivation of Gluconeogenetic Enzymes in Saccharomyces cerevisiae

Abstract

The mechanism of catabolite inactivation of 3 gluconeogenetic enzymes, fructose-1,6-bisphosphatase, cytoplasmic malate dehydrogenase and phosphoenolpyruvate carboxykinase, was studied in the yeast S. cerevisiae. The glucose-induced inactivation of the 3 enzymes is remarkably retarded by preincubation of the cells with different caffeine concentrations; a full conservation of activity has never been obtained, even at the highest drug concentration. Caffeine modifies the metabolic effects produced in the yeast cell by exposure to glucose. It reduces the consumption rate of glucose, changes the glycolytic intermediate pattern (giving rise to a crossover point at the level of the phosphofructokinase/fructose-bisphosphatase cycle), and increases the ATP level and the energy charge. It substantially reduces the peak of intracellular cAMP content that immediately follows glucose entry; the magnitude of this effect is dependent on the drug concentration. The effect on the change of intracellular cAMP level appears, among all metabolic effects determined by caffeine, the only plausible one to explain the interference with catabolite inactivation of enzymes. Actually a strong negative correlation between residual activity of each of the 3 investigated enzymes and intracellular cAMP level was demonstrated. The existence of a common mechanism of action of cAMP, as the mediating factor for catabolite inactivation of all 3 enzymes, is proposed.