title: The inhibitory guanine nucleotide-binding regulatory component of adenylate cyclase. Subunit dissociation and guanine nucleotide-dependent hormonal inhibition.
abstract: The inhibitory and stimulatory guanine nucleotide-binding regulatory components (Gi and Gs) of adenylate cyclase both have an alpha X beta subunit structure, and the beta (35,000 Da) subunits are functionally indistinguishable. Gi and Gs both dissociate in the presence of guanine nucleotide analogs or Al3+, Mg2+, and F- in detergent-containing solutions. Several characteristics of Gi- and Gs-mediated regulation of adenylate cyclase activity have been studied in human platelet membranes. The nonhydrolyzable analog of GTP, guanosine-5'-(3-O-thio)triphosphate (GTP gamma S) mimics GTP-dependent hormonal inhibition or stimulation of adenylate cyclase under appropriate conditions. This inhibition or stimulation follows a lag period. The combined addition of epinephrine or prostaglandin E1 with GTP gamma S results in the immediate onset of steady state inhibition or activation. The effects of the GTP analog are essentially irreversible. Fluoride is also an effective inhibitor of prostaglandin E1-stimulated adenylate cyclase, while it markedly stimulates the basal activity of the enzyme. The addition of the resolved 35,000-Da subunit of Gi to membranes results in inhibition of adenylate cyclase, and the resolved 41,000-Da subunit has a stimulatory effect on enzymatic activity. The inhibitory action of the 35,000-Da subunit is almost completely abolished in membranes that have been irreversibly inhibited by GTP gamma S plus epinephrine; this irreversible inhibition is almost completely relieved by the 41,000-Da subunit. Detergent extracts of membranes that have been treated with GTP gamma S plus epinephrine contain free 35,000-Da subunit. The 41,000-Da subunit of Gi contained in such extracts has a reduced ability to be ADP-ribosylated by islet-activating protein (IAP), which implies that this subunit is in the GTP gamma S-bound form. The irreversible inhibition of adenylate cyclase caused by GTP gamma S (plus epinephrine) in membranes is highly correlated with the liberation of free 35,000-Da subunit activity and is inversely related to the 41,000-Da IAP substrate activity in detergent extracts prepared therefrom. The increase in free 35,000-Da subunit activity in extracts and the inhibition of adenylate cyclase activity in GTP gamma S (plus epinephrine)-treated membranes are both markedly inhibited by treatment with IAP.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000097:blood; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000097:blood; D001792:Blood Platelets / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology; D004837:Epinephrine / Q000494:pharmacology; D019204:GTP-Binding Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors* / Q000097:blood; D013873:Thionucleotides / Q000494:pharmacology*
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D046911:Macromolecular Substances; D011956:Receptors, Cell Surface; D013873:Thionucleotides; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D004837:Epinephrine