Table I. Effect of cAMP, (S_p)-cAMPS, and (R_p)-cAMPS on association and dissociation rate constants for C-subunit binding to FM-R92C RIα(91–244).

	k1a	k−1b	Kdc
	m−1s−1	s−1	m
Control	2.0 ± 012 × 107	3.8 ± 0.1 × 10−3	1.9 × 10−10
cAMP	1.7 ± 0.11 × 107	0.55 ± 0.05	3.2 × 10−8
(Rp)-cAMPS	1.9 ± 0.17 × 107	7.5 ± 0.3 × 10−4	4.0 × 10−11
(Sp)-cAMPS	1.9 ± 0.16 × 107	0.75 ± 0.02	4.0 × 10−8

^a Bimolecular association rate constants determined from rapid mixing of FM-labeled RIα(91–244) mutants (100 nm) with various concentrations of C-subunit in the absence and presence of cAMP (10 μm), (R_p)-cAMPS (100 μm), or (S_p)-cAMPS (100 μm) under pseudo first-order conditions (n = 4).

^b Unimolecular dissociation rate constants determined by rapidly mixing excess unlabeled RIα(91–244) with preformed RIα(91–244)·C complex (100 nm) of FM-labeled RIα(91–244) conjugates and C-subunit in the absence and presence of cAMP (10 μm), (R_p)-cAMPS (100 μm), or (S_p)-cAMPS (100 μm) (n = 3).

^c Equilibrium dissociation constants determined by dividing the unimolecular dissociation by the bimolecular association rate constants.