How does glucose initiate proteolysis of yeast fructose-1,6-bisphosphatase?

Glucose-induced proteolysis of fructose-1,6-bisphosphatase (FBPase) in yeast (Funayama, S. et al. (1980) Eur. J. Biochem. 109, 61-66) is preceded by rapid phosphorylation of the enzyme (Müller, D., and Holzer, H. (1981) Biochem. Biophys. Res. Commun. 103. 926-933; Mazón, M. J. et al. (1982) J. Biol. Chem. 257, 1128-1130). The postulated sequence of events is as follows. Glucose causes a decrease of the cytosolic pH from 7.0 to about 6.5 (Purwin, C. et al. (1986) J. Biol. Chem. 261, in press). The change in pH activates adenylate cyclase which is at pH 6.5 2-3 times more active than at pH 7.0 The concentration of cAMP increases 2-5 times (Purwin, C. et al. (1982) Biochem. Biophys. Res. Commun. 107, 1482-1489) and thereby activates a protein kinase which phosphorylates FBPase (Pohlig, G., and Holzer, H. (1985) J. Biol. Chem. 260, 13818 to 13823). The phosphorylated enzyme is either proteolyzed in the cytosol or taken up into the vacuoles, the compartment where unspecific proteolysis takes place.