FIGURE 7.

Dependences of the observed fast and slow rates for bimolecular CO binding and fraction of the fast phase on [CO] for both laser photolysis and rapid mixing experiments with isolated Trp-58(E7) α subunits. A, dependence of k_fast (open circles) and f_fast (open squares) on [CO]. B, dependence of k_slow (light gray symbols) and k_ultraslow (dark symbols) on [CO]. The diamonds represent rates determined in stopped flow, rapid mixing experiments with the equilibrium deoxy forms of the Trp(E7) α subunits. The light gray circles for the slow rates represent data from laser photolysis experiments. Black lines represent fits to the model described in Scheme 2, and the fitted parameters are listed in the text after Equation 6. The rates for the ultraslow phase were fit using the model described in the supplementary material (Section A3 (Scheme 2c)). The fitted rate constants for the interconversion of the slow α subunit forms are as follows: k_s = 610 s⁻¹, k_−s = 200 s⁻¹. The dashed line represents a fit to Scheme 1, which requires a hyperbolic dependence of k_slow on [CO]. The experimental conditions were 100 mm sodium phosphate, pH 7, 20 °C.