Table 1.

Rates of GTPγS binding to Hexa I Gαi1 and Hexa I R1-Gαi1

Mutant*	R1 sites†	GTPγS binding,‡ min−1
		Nat	R1	R1 + Ric-8A
Gαi1	—	0.043	—	0.56 (43)
Hexa I Gαi1	—	0.021	—	0.28 (32)
90C,106C	H	0.018	0.019	0.22 (25)
90C,214C	H-R	0.024	0.018	0.27 (24)
90C,238C	H-R	0.025	0.015	0.32 (32)
106C-214C	H-R	0.019	0.025	0.33 (35)
106C-238C	H-R	0.033	0.029	0.35 (32)
147C-235C	H-R	0.025	0.02	0.29 (32)
63C-238C	H-R	0.016	0.016	0.11 (28)
63C-209C	H-R	0.022	0.022	0.29 (29)
43C-330C	R	0.042	0.04	0.50 (34)
180C-305C	R	0.023	0.02	0.28 (29)
209C-330C	R	0.033	0.031	0.36 (30)
305C-330C	R	0.041	0.032	0.49 (35)

^*All R1 pairs are in the Hexa I Gαi1 background.

^†H, both R1 residues in Helical domain; H-R, one R1 residue in helical and one R1 in Ras domain; R, both R1 residues in Ras domain.

^‡Nat, unlabeled cysteine mutant in Hexa I background; R1, R1-derivatized cysteine mutant in Hexa I background; R1 + Ric-8A, R1-derivatized mutant in the presence of Ric-8A (see Materials and Methods for assay conditions). Values of individual measurements are within 5% of the average value. Overall percent change in tryptophan fluorescence after 10 min of incubation with GTPγS is shown in parenthesis.