The inhibitory guanine nucleotide-binding regulatory component of adenylate cyclase. Properties and function of the purified protein

T. Katada, G. M. Bokoch, J. K. Northup, M. Ui, A. G. Gilman

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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 α2-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 A13+, 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 GTPγS-bound form of the 41,000-Da subunit inhibits adenylate cyclase activity, although the lower apparent affinity than does the 35,000-Da subunit. (5) The 35,000-Da subunit increases the rate of deactivation of G(s), the stimulatory regulatory protein of adenylate cyclase. In contrast, the 41,000-Da subunit can interact with G(s) 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.

Original languageEnglish (US)
Pages (from-to)3568-3577
Number of pages10
JournalJournal of Biological Chemistry
Volume259
Issue number6
StatePublished - May 24 1984

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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