Figure 4.

Analysis of the chromophore exchange rates. (A) Derivation of the dissociation rate constant (k_off): the fraction of Rho dissociation in the chromophore exchange measurement was plotted versus the incubation time at 28°C (square), 36°C (circle), and 44°C (diamond, corrected for the denaturation of opsin) and fitted using a monoexponential model. (B) Eyring plot for the chromophore dissociation kinetics is shown. The exchange rate at 44°C was corrected for contribution of opsin denaturation as described in the Supporting Material. The activation enthalpies derived from the corrected data (solid line) and the uncorrected data (dash line) are 38.5 ± 4.4 kcal mol⁻¹ and 33.5 ± 1.4 kcal mol⁻¹, respectively.