Geminate reactions of oxygen and nitric oxide with the α and β subunits of the Fe-Co hybrid hemoglobins

The α and β subunits in Fe-Co hybrid hemoglobins differ in their rapid reactions with dioxygen and nitric oxide after dissociation by a 25-ns photoflash. The α subunits show little recombination on a scale of tens of nanoseconds, whereas the β subunits show extensive recombination on this time sale. The α-β difference is more marked with Fe than with Co and greater with dioxygen as ligand than with nitric oxide, but is clearly evident in all combinations of ligand and metal. Addition of inositol hexaphosphate slows ligand binding and reduces the proportion of rapid recombination of dioxygen and nitric oxide to β-Fe subunits. The behavior of α-Fe subunits is unaffected by this compound. These results permit the β subunit to be identified as the T-state species which equilibrates rapidly with oxygen in the T-state, i.e. the reverse of the identification suggested on structural grounds.