| Abstract: | The catalytic moiety of hormone-sensitive adenylate cyclase has been purified from bovine brain. It is isolated largely without its guanine nucleotide-binding regulatory protein, Gs, by affinity chromatography on 7-O-hemisuccinyldeacetylforskolin-agarose. It appears to be a single polypeptide which migrates on sodium dodecyl sulfate-polyacrylamide gels with an apparent Mr of approximately 120,000. When subjected to electrophoresis on gradient (5-10%) sodium dodecyl sulfate-polyacrylamide gels, it displays a larger apparent Mr of 150,000. The adenylate cyclase activity of the preparation can be stimulated by the addition of Gs, forskolin, or calcium-calmodulin. The preparation has been reconstituted with purified beta-adrenergic receptors and Gs to form a hormone-stimulated adenylate cyclase system (May, D., Ross, E.M., Gilman, A.G., and Smigel, M.D. (1985) J. Biol. Chem. 260, 15829-15833). In contrast to its stimulation by Gs, inhibition by the alpha subunits of Gi and Go, G proteins known to be coupled to inhibitory receptors (Sternweis, P., and Florio, V. (1985) J. Biol. Chem. 260, 3477-3483), is not seen. Preparations of adenylate cyclase show varying degrees of inhibition by added G protein beta . gamma subunit. This inhibition can be explained as reflecting a variable, small (under 5%) contamination of the preparation by Gs alpha which would be deactivated by complexing with the added beta . gamma subunit. |
