FIGURE 3.

Bimolecular CO binding to Trp-64(E7) sperm whale Mb. A, time courses for bimolecular CO rebinding to ∼50 μm Trp-64(E7) Mb after complete photolysis by the 0.5-μs dye laser at [CO] = 1000 and ∼50 μm. The fitted and estimated observed pseudo-first order rate constants were ∼700 s⁻¹ and ∼35 s⁻¹, respectively. B, dependence of the pseudo-first order rate constant on [CO] for CO binding to the equilibrium deoxygenated form of Trp-64(E7) Mb measured in stopped flow, rapid mixing experiments at low ligand concentrations. The slope of the fitted line gives an association rate constant equal to 0.69 μm⁻¹ s⁻¹, which is identical to the value computed from the laser photolysis data in A.