Table 3.

Rate constants of [³⁵S]GTP-γS binding in GDP-less membranes

	kobs[h−1]	Beq[fmol·µg−1protein]	koff[h−1]
GDP-less membranes	4.35 ± 0.15	5.66 ± 0.22	0.324 ± 0.013
+100 µM carbachol	4.33 ± 0.17	5.70 ± 0.25	0.327 ± 0.014
50 µM GDP	1.34 ± 0.14*	1.21 ± 0.12*	0.334 ± 0.012
+100 µM carbachol	3.98 ± 0.14*a	4.85 ± 0.19*a	0.322 ± 0.012
+100 nM NMS	1.01 ± 0.08a	1.20 ± 0.11	0.343 ± 0.009

Constants were obtained by fitting Equations 5a or 6a as appropriate to data from individual experiments shown in Figure 3. k_obs, association rate constant; B_eq, binding at equilibrium; k_off, dissociation rate constant. Data are means ± SEM of values from three independent experiments performed in quadruplicates.

^*P < 0.01; significantly different from control (GDP vs. GDP-less, with vs. without carbachol) and

^aP < 0.05; significantly different from control without ligand by t-test.

GDP, guanosine diphosphate; GTPγS, guanosine-5′-γ−thiotriphosphate; NMS, N-methylscopolamine.