Abstract
We have measured the absolute quantum yield of the oxyhemoglobin photodissociation with a 30 ps laser pulse excitation. We report that oxyhemoglobin dissociates with the same yield as carboxymyoglobin under photostationary conditions. Based on the picosecond and nanosecond experimental data, we show that oxygen geminate recombination is responsible for the low quantum yield values of oxyhemoglobin photodissociation measured with longer photolysis flashes. Kinetic data suggest that two geminate regimes which successively appear in oxygen recombination can be resolved. The first can be entirely attributed to the hemoglobin-iron chemical reactivity and, the second to the action of protein fluctuations.