title: The inhibitory guanine nucleotide-binding regulatory component of adenylate cyclase. Properties and function of the purified protein.
abstract: Treatment of membranes with islet activating protein (IAP), a toxin from Bordetella pertussis, results in abolition of GTP-dependent, receptor-mediated inhibition of adenylate cyclase. This appears to result from IAP-catalyzed ADP-ribosylation of a 41,000-Da membrane-bound protein. A protein with 41,000- and 35,000-Da subunits has been purified from rabbit liver membranes as the predominant substrate for IAP. This protein has now been shown to be capable of regulating membrane-bound adenylate cyclase activity of human platelets under various conditions. The characteristics of the actions of the IAP substrate are as follows. 1) Purified 41,000/35,000-Da dimer is capable of restoring the inhibitory effects of guanine nucleotides and the alpha 2-adrenergic agonist, epinephrine, on the adenylate cyclase activity of IAP-treated membranes. 2) The subunits of the dimer dissociate in the presence of guanine nucleotide analogs or A1(3+), Mg2+, and F-. The 41,000-Da subunit has a high affinity binding site for guanine nucleotides. 3) The resolved 35,000-Da subunit of the dimer mimics guanine nucleotide- and epinephrine-induced inhibition of adenylate cyclase. 4) The resolved (unliganded) 41,000-Da subunit stimulates adenylate cyclase activity and relieves guanine nucleotide- +/- epinephrine-induced inhibition of the enzyme. In contrast, the GTP gamma S-bound form of the 41,000-Da subunit inhibits adenylate cyclase activity, although with lower apparent affinity than does the 35,000-Da subunit. 5) The 35,000-Da subunit increases the rate of deactivation of Gs, the stimulatory regulatory protein of adenylate cyclase. In contrast, the 41,000-Da subunit can interact with Gs and inhibit its deactivation. These data strongly suggest that the IAP substrate is another dimeric, guanine nucleotide-binding regulatory protein and that it is responsible for inhibitory modulation of adenylate cyclase activity.
mesh_terms: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000097:blood*; D000527:Alprostadil; D000959:Antihypertensive Agents / Q000494:pharmacology; D001427:Bacterial Toxins / Q000494:pharmacology; D001792:Blood Platelets / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology; D005576:Colforsin; D004224:Diterpenes / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D037342:Pertussis Toxin; D011458:Prostaglandins E / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000097:blood*; D012969:Sodium Fluoride / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella
chemical_list: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000959:Antihypertensive Agents; D001427:Bacterial Toxins; D004224:Diterpenes; D011458:Prostaglandins E; D011956:Receptors, Cell Surface; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D012969:Sodium Fluoride; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D000527:Alprostadil; D008274:Magnesium