Glucose-induced activation of plasma membrane H +-ATPase in mutants of the yeast Saccharomyces cerevisiae affected in cAMP metabolism, cAMP-dependent protein phosphorylation and the initiation of glycolysis

Abstract

Addition of glucose-related fermentable sugars or protonophores to derepressed cells of the yeast Saccharomyces cerevisiae causes a 3- to 4-fold activation of the plasma membrane H +-ATPase within a few minutes. These conditions are known to cause rapid increases in the cAMP level. In yeast strains carrying temperature-sensitive mutations in genes required for cAMP synthesis, incubation at the restrictive temperature reduced the extent of H +-ATPase activation. Incubation of non-temperature-sensitive strains, however, at such temperatures also caused reduction of H +-ATPase activation. Yeast strains which are specifically deficient in the glucose-induced cAMP increase (and not in basal cAMP synthesis) still showed plasma membrane H +-ATPase activation. Yeast mutants with widely divergent activity levels of cAMP-dependent protein kinase displayed very similar levels of activation of the plasma membrane H +-ATPase. This was also true for a yeast mutant carrying a deletion in the CDC25 gene. These results show that the cAMP-protein kinase A signaling pathway is not required for glucose activation of the H +-ATPase. They also contradict the specific requirement of the CDC25 gene product. Experiments with yeast strains carrying point or deletion mutations in the genes coding for the sugar phosphorylating enzymes hexokinase PI and PII and glucokinase showed that activation of the H +-ATPase with glucose or fructose was completely dependent on the presence of a kinase able to phosphorylate the sugar. These and other data concerning the role of initial sugar metabolism in triggering activation are consistent with the idea that the glucose-induced activation pathways of cAMP-synthesis and H +-ATPase have a common initiation point.