ON THE MECHANISM BY WHICH A HEAT-SHOCK INDUCES TREHALOSE ACCUMULATION IN SACCHAROMYCES-CEREVISIAE

When the temperature of exponential-phase cultures of Saccharomyces cerevisiae was abruptly raised from 28 to 40-degrees-C, trehalose immediately accumulated, whereas the activities of trehalase and trehalose-6-phosphate synthase/trehalose-6-phosphate phosphatase complex increased after a lag period of about 10 min. Heat shock also induced a sudden rise in intracellular glucose, simultaneously with a decrease in the concentration of hexose phosphate and fructose 2,6-bisphosphate. The increase of trehalose-metabolizing enzymes, but not the accumulation of glucose and trehalose, was prevented by cycloheximide. Investigation of the kinetic properties of partially purified enzymes showed that both nonactivated and cyclic AMP-dependent-protein-kinase-activated forms of trehalase are almost inactive in the absence of Ca2+ and that the concentration of free Ca2+ required for half-maximal activity increased with increasing temperature, being approx. 1 mum at 30-degrees-C and 20 mum at 40-degrees-C for the activated form of trehalase. In contrast, trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase were three times more active at 40-degrees-C. It is proposed that the rapid accumulation of trehalose induced by heat shock may be in part explained by changes in the kinetic properties of trehalase and trehalose-6-phosphate synthase/trehalose-6-phosphate phosphatase.