The kinetics of the recombination reaction between 11CR and opsin. (A) The kobs of Rho regeneration was measured at various concentrations of 11CR (molar ratio of retinal to the receptor: 8.0 to 64). The slope of the plot corresponds to the k2 ((1.21 ± 0.04) × 103 M−1 s−1 at 28°C). (B) The measured k2 of Rho regeneration is inversely correlated with the concentrations of lipids (α = (1.21±0.05)×104 s−1). (C) Eyring plot for the second-order rate constants of three purified Rho samples: 1) Rho from bovine ROS (ROS Rho, Trp-based assay), 2) Rho heterologously expressed in HEK293F cells (PMT4 Rho, Trp-based assay), and 3) S144azF mutant Rho labeled with an Alexa488 fluorophore (S144-Alexa488 Rho, Alexa488-based assay).