Summary: Derepressed cells of suspended in buffer exhibited both a transient cAMP-mediated signal and a marked activation of cytoplasmic trehalase when supplemented with glucose. Nitrogen sources or protein 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 the cAMP signal and the glucose-induced activation of trehalase without affecting the increase in trehalase activity caused by nitrogen sources or protein synthesis inhibitors. These results suggest that cAMP is not involved as second messenger in the signal for trehalase stimulation induced by the latter compounds. By contrast, the addition of glucose to repressed cells suspended in buffer failed to cause the cAMP-mediated glucose signal and sugar-induced trehalase activation. No significant changes in either trehalase activity or cAMP concentration were observed upon addition to these cells of asparagine, cycloheximide, anisomycin or other agents, including protonophores and uncouplers. However, heat treatment of repressed cultures resulted in a moderate increase in trehalase activity with negligible change in cAMP levels, whereas such an effect was not observed in derepressed cultures. The thermally induced increase in trehalase activity was dependent on protein synthesis and required the presence of glucose. Since in all cases the enzyme activated was deactivated by phosphatase our data support the idea that in there are at least three independent mechanisms to increase trehalase activity, involving different, but overlapping, phosphorylation pathways.


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