Table I Effect of cAMP, (Sp)-cAMPS, and (Rp)-cAMPS on association and dissociation rate constants for C-subunit binding to FM-R92C RIα(91–244)
k1ak−1bKdc
m1 s1s1m
Control2.0 ± 012 × 1073.8 ± 0.1 × 10−31.9 × 10−10
cAMP1.7 ± 0.11 × 1070.55 ± 0.053.2 × 10−8
(Rp)-cAMPS1.9 ± 0.17 × 1077.5 ± 0.3 × 10−44.0 × 10−11
(Sp)-cAMPS1.9 ± 0.16 × 1070.75 ± 0.024.0 × 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), (Rp)-cAMPS (100 μm), or (Sp)-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), (Rp)-cAMPS (100 μm), or (Sp)-cAMPS (100 μm) (n = 3).

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