Fig. 2.

M2 receptor stimulation of GTPγS binding to G protein is inhibited by γ5pep-gg. M2 receptors in membrane suspension were preincubated with G-protein in the presence or absence of geranylgeranylated γ5 peptides as described under Materials and methods. The final concentrations of receptor and G protein were 5 nM M2 and 100 nM Gi2 heterotrimer. Binding reactions were started by the addition of [³⁵S] GTPγS and agonist (carbachol) or antagonist (atropine). Aliquots were taken and Gα in complex with [³⁵S] GTPγS measured as described under Materials and methods. Bars represent mean ± SEM (n ≥ 3). Asterisks denote that the activities in the presence of γ5pep-gg are significantly lower (p < 0.05) than the activities in the presence of γ5pep-gg-scr. Statistical analysis was performed as described under Materials and methods.