LACK OF CORRELATION BETWEEN TREHALASE ACTIVATION AND TREHALOSE-6 PHOSPHATE SYNTHASE DEACTIVATION IN CAMP-ALTERED MUTANTS OF SACCHAROMYCES-CEREVISIAE

The rise in cAMP level that follows the addition of glucose or 2,4-din itrophenol (DNP) to stationary-phase cells of Saccharomyces cerevisiae was accompanied by a marked activation of trehalase (3-fold increase) and a concomitant deactivation of trehalose-6 phosphate synthase (50% of the basal levels). In glucose-grown exponential cells, which are d eficient in glucose-induced cAMP signalling, the addition of glucose a lso prompted a decrease in trehalose-6 phosphate synthase. but had no effect on trehalase activity. Mutants defective in the RAS-adenylate c yclase pathway (ras1 ras2 bcy1 strain), as well as mutants containing greatly reduced protein kinase activity either cAMP-dependent (tpk(w1) BCY1 strains) or cAMP-independent (tpk1w1 bcy1 strains), were unable to show glucose- or DNP-induced trehalase activation but still display ed a clear decrease in trehalose-6 phosphate synthase activity upon ad dition of these compounds. These data suggest that the activity of tre halose-6 phosphate synthase, as opposed to that of trehalase, is not c ontrolled by the cAMP signalling pathway ''in vivo''. Trehalose-6 phos phate synthase was competitively inhibited by glucose (Ki = 15 mM) and resulted unaffected by ATP in assays performed ''in vitro''.