FIGURE 1.

CO binding to Trp(E7) mutants of the α and β subunits of human HbA. A, bimolecular rebinding to ∼100 μm native HbA, α(Trp-58(E7))β(WT), and α(WT)β(Trp-63(E7)) tetramers at [CO] = 1000 μm, after complete photolysis with a 0.5-μs excitation pulse from an Phase-R model 2100B dye laser, which “pumps” all of the ligands into the solvent phase. B, slow phases for bimolecular CO rebinding to ∼50 μm isolated Trp(E7) α and β subunits at 1000 μm CO after complete photolysis; the inset shows the rapid bimolecular binding phases, which occur on a microsecond time scale. C, stopped flow, rapid mixing experiments for CO binding to equilibrium deoxygenated forms of ∼5 μm isolated Trp(E7) α and β subunits at [CO] = 200 μm after mixing. The light gray lines in B and C represent fits to single or multiple exponential expressions. Conditions were 100 mm sodium phosphate, pH 7, 20 °C.