Geminate recombination in carboxy hemoglobin A and its relation to overall carbon monoxide reactivity

The geminate recombination of CO with carboxy hemoglobin (Hb4(CO)3) following a ten nanosecond laser pulse and the overall combination of the fourth CO with Hb4(CO)3 has been studied as a function of pH in the presence and absence of inositol hexaphosphate. The results indicate that the kinetics of both reactions are independent of pH and phosphate concentration. The results are discussed in terms of a two-step mechanism: a pre-equilibrium step followed by heme--ligand bond formation. The latter is also known as the geminate recombination reaction (Hb + CO in equilibrium Hb X CO in equilibrium HbCO).