Subunit dissociation is the mechanism for hormonal activation of the Gs protein in native membranes.

We have recently reported (Ransnäs, L.A., and Insel, P.A. (1988) J. Biol. Chem. 263, 9482-9485) development of antipeptide antibodies to the alpha s protein of the stimulatory guanine nucleotide binding regulatory protein, Gs, and use of one of these antibodies, GS-1, to quantitate Gs levels in S49 lymphoma cell membranes. Another of these antibodies, termed GS-2, appears to detect only dissociated alpha s, but not the heterotrimer alpha s beta gamma. Using a competitive enzyme-linked immunosorbent assay, we have found that the guanine nucleotides GTP and guanosine 5'-O-(thiotriphosphate) (GTP gamma S) (but not GDP) and the beta-adrenergic receptor agonist isoproterenol activate Gs in native S49 cell membrane by subunit dissociation. Evidence for this includes detection of dissociated alpha s in membrane extracts and release of alpha s from S49 cell membranes treated with GTP gamma S or isoproterenol. Moreover, the estimates of apparent stoichiometry for this dissociation indicate that each beta-adrenergic receptor is able to activate greater than or equal to 100 molecules of Gs in native membranes. Thus, receptor-mediated dissociation of Gs is likely to be the major site of amplification of signal transduction by agonists active at hormone receptors that link to Gs.