Geminate recombination of diatomic ligands CO, O2, and NO with myoglobin

The kinetics of geminate recombination of horse heart myoglobin with the diatomic ligands carbon monoxide, dioxygen, and nitric oxide have been reexamined. The new measurements are distinguished from previous studies by (1) consideration of the complete time range longer than 1 ps, (2) inclusion of the effect of temperature changes near ambient, (3) attention to the relation between recombination kinetics and the yield of dissociated partners on the millisecond time scale, and (4) use of singular value decomposition in the analysis. These picosecond results, together with earlier nanosecond data, for O2 prove that models incorporating one, two, or even three discrete intermediates are not sufficient to account for all features of geminate recombination kinetics. Instead, a continuous evolution of the geminate pair distribution is preferred.