HISTONE II-A ACTIVATES THE GLUCOSE-6-PHOSPHATASE SYSTEM WITHOUT MICROSOMAL MEMBRANE PERMEABILIZATION

Many agents have been used to release the latent portion of the activi ties catalyzed by the glucose-6-phosphatase (Glc-6-Pase) system. Deter gents, which disrupt the microsomal membrane concomitantly with Glc-6- Pase activation, have been the most widely used of these agents. The t reatment of microsomes with alamethicin or histone II-A has also been reported to activate the Glc-6-Pase system to the same extent as deter gent treatment. While alamethicin reportedly permeabilizes the microso mal membrane (R Fulceri et al., 1995, Biochem. J. 307, 391-397), confl icting ideas as to histone II-A's mechanism of activation have been de scribed (J. St.-Denis et al, 1995, Biochem. J. 310, 221-224 and J. Bla ir and A. Burchell, 1988, Biochim. Biophys. Acta 964, 161-167). We fur ther investigated whether activation of the Glc-6-Pase system by histo ne II-A is due to permeabilization of the microsomal membrane. We trea ted rat liver microsomes with Triton X-100, alamethicin, or histone II -A and found them to be equally effective in maximally activating the Glc-6-Pase system, We also examined the modifying effects of alamethic in and histone II-A on the sensitivity of Glc-6-Pase activities to inh ibition by N-bromoacetylethanolamine phosphate (BAEP) and 3-mercaptopi colinate (3-MP), both thiol-directed reagents. Alamethicin, but not hi stone II-A, abolished the inhibitory effects of BAEP and 3-MP on activ ities of the Glc-6-Pase system, Our studies support previous reports o f Glc-6-Pase activation by alamethicin via permeabilization of microso mal membranes and histone II-A activation without microsomal membrane permeabilization. (C) 1998 Academic Press.