ACTIVATION OF CYTOPLASMIC TREHALASE BY CYCLIC-AMP-DEPENDENT AND CYCLIC-AMP-INDEPENDENT SIGNALING PATHWAYS IN THE YEAST CANDIDA-UTILIS

Derepressed cells of Candida utilis suspended in buffer exhibited both a transient cAMP-mediated signal and a marked activation of cytoplasm ic trehalase when supplemented with glucose. Nitrogen sources or prote in synthesis inhibitors, as well as protonophores or uncouplers, were also able to cause trehalase stimulation in derepressed cells even in the absence of the sugar. The increase in trehalase activity caused by nitrogen sources or protein synthesis inhibitors was not accompanied by changes in cAMP levels. Moreover, acridine orange inhibited both th e cAMP signal and the glucose-induced activation of trehalase without affecting the increase in trehalase activity caused by nitrogen source s or protein synthesis inhibitors. These results suggest that cAMP is not involved as second messenger in the signal for trehalase stimulati on induced by the latter compounds. By contrast, the addition of gluco se to repressed cells suspended in buffer failed to cause the cAMP-med iated glucose signal and sugar-induced trehalase activation. No signif icant changes in either trehalase activity or cAMP concentration were observed upon addition to these cells of asparagine, cycloheximide, an isomycin or other agents, including protonophores and uncouplers. Howe ver, heat treatment of repressed cultures resulted in a moderate incre ase in trehalase activity with negligible change in cAMP levels, where as such an effect was not observed in derepressed cultures. The therma lly induced increase in trehalase activity was dependent on de novo pr otein synthesis and required the presence of glucose. Since in all cas es the enzyme activated in vivo was deactivated in vitro by phosphatas e our data support the idea that in C. utilis there are at least three independent mechanisms to increase trehalase activity, involving diff erent, but overlapping, phosphorylation pathways.