Properties and Possible Functions of the Adenylate Cyclase in Plasma Membranes ofSaccharomyces cerevisiae

Abstract

We have examined the possible role of adenosine 3′,5′-phosphate (cAMP) in functions associated with the plasma membranes ofSaccharomyces cerevisiae.Purified membranes from this source contained an adenylate cyclase which was insensitive to activation by fluoride or guanine nucleotides, only weakly responsive to changes of carbon source in the growth medium, and strongly stimulated by vanadate. They also contained at least two classes of receptor proteins for guanine nucleotides (as measured by binding of labeled 5′-guanylyl methylene diphosphate) with apparent dissociation constants equal to 1.0 × 10−7and 3 × 10−6M, a protein kinase capable of phosphorylating added histones, the activity of which was stimulated by cAMP, and cAMP receptors that may function as regulatory subunits for this kinase. Membrane proteins were also susceptible to phosphorylation by endogenous kinase(s), with polypeptides of apparent molecular weights equal to 160 × 103, 135 × 103, 114 × 103, and 58 × 103as the major targets. Of these, the 114,000-molecular-weight polypeptide was probably identical to the proton-translocating ATPase of the membranes. However, the cAMP-dependent protein kinase did not appear to be involved in these reactions. Intact (rho+orrho0) cells responded to dissipation of the proton electrochemical gradient across their plasma membranes by rapid and transient changes in their intracellular level of cAMP, as suggested earlier (J. M. Trevillyan and M. L. Pall, J. Bacteriol.,138:397-403, 1979). Thus, although yeast plasma membranes contain all the essential components of a stimulus-responsive adenylate cyclase system, the precise nature of the coupling device and the targets involved remain to be established.