Inactivation of the CDC25 gene product in Saccharomyces cerevisiae leads to a decrease in glycolytic activity which is independent of cAMP levels.

In the budding yeast Saccharomyces cerevisiae cyclic AMP (cAMP) can influence the activity of key enzymes in carbohydrate metabolism through modulation of the activity of cAMP-dependent protein kinase. One of the components involved in cAMP production is the CDC25 gene product, which can activate the RAS/adenylate cyclase pathway by promoting the exchange of guanine nucleotides bound to RAS. In two yeast strains carrying different thermosensitive alleles of the CDC25 gene, cAMP levels respond differently to an increase in growth temperature from 23 degrees C (permissive) to 36 degrees C (restrictive). In strain OL86 (cdc25-5) the estimated intracellular concentration of cAMP dropped after transfer to restrictive temperature whereas in strain ts321 (cdc25-1) the cAMP level rose under the same conditions. Despite the differences in cAMP levels the glycolytic flux in the two mutants responded in a very similar way to the shift from permissive to restrictive temperature; after the increase in the incubation temperature, the specific glycolytic flux in both cdc25-1 and cdc25-5 initially increased from about 300 nmol min-1 (mg protein)-1 to about 500 nmol min-1 (mg protein)-1 (presumably mainly as a consequence of the increase in temperature), but then gradually fell to 100-200 nmol min-1 (mg protein)-1. A similar pattern of CO2 production to that found in the two cdc25 mutants was also observed for several other thermosensitive mutants displaying a Start-II type of G1 arrest. In contrast, in a wild-type strain and in strains giving a Start-I type of G1 arrest, CO2 production did not drop after a temperature shift. The specific activities of glycolytic enzymes in the two cdc25 mutants did not show much change after the temperature shift, indicating that the decrease in glycolytic flux was not caused by a decrease in the activity of any of the glycolytic enzymes. Our data show that, at least in long-term regulation, the cAMP levels per se are not likely to be a prime factor controlling glycolytic flux.