Conformational relaxation and ligand binding to singly reduced human embryonic haemoglobins.

The reaction of the three human embryonic haemoglobins with aquated electrons follows a complex set of steps in which a single haem centre undergoes both reduction and spin state changes coupled to slower protein relaxation events. In the presence of ferrous haem ligands the spin state changes are coupled directly to the ligand binding process. The rate constants for the reaction of the single reduced haem with O2 are similar to those determined by flash photolysis at high pH, whilst CO binding to the beta type haems is more rapid and the alpha haems less rapid than the analogous processes observed using photolysis techniques.