Cyclic AMP and Catabolite Repression in Yeasts

In Schizosaccharomyces pombe an inverse proportionality between glucose concentration and intracellular adenosine 3′:5′‐monophosphate (CAMP) was established. The cAMP levels were in the range of 12 to 785 pmol per g yeast cells dry weight. In continuous cultures a steady‐state concentration of as low as 0.05% glucose is sufficient to cause a decrease in intracellular cAMP content. Lowest levels of CAMP were found in the presence of more than 5% glucose, while highest levels were synthesized by cells grown on glycerol or maltose. In all strains tested, CAMP is transported into the fermentation broth, both if grown on glucose or cultured on maltose as the sole carbon source. The synthesis of α‐glucosidase (EC 3.2.1.20) is induced by maltose. Glucose represses the synthesis of invertase (EC 3.2.1.26), NADH‐ferricyanide reductase (EC 1.6.99.3) and both the constitutive and the inducible α‐glucosidase. The possibility of a coordinate synthesis of α‐glucosidases and invertase is indicated by the experimental data but cannot definitely be proved. Moreover, there exists a relation between the intracellular concentration of cAMP and the activities of invertase, α‐glucosidases and a NADH‐ferricyanide reductase. Under comparable growth conditions a mutant strain partially resistant to catabolite repression synthesizes more cAMP and produces increased activities of the catabolite‐sensitive enzymes tested than the wild‐type strain. Strains classified as catabolite‐sensitive show reduced values of intracellular cAMP and enzyme activities. In contrast to Saccharomyces cerevisiae in Schizosaccharomyces pombe there exists no relation between the intracellular level of cAMP and the activity of alcohol dehydrogenase (EC 1.1.1.1). We suppose, that in Schizosaccharomyces pombe cAMP is concerned with the regulation of catabolite‐sensitive enzyme synthesis.