Electronic Control of Ferroporphyrin Ligand-Binding Kinetics

Measurements of the rates of CO binding to ferrous porphyrins have been used to examine two different mechanisms which have been proposed to explain protein control of heme reactivity. The results indicate that electronic control through ω-donor/acceptor interactions with the macrocyclic porphyrin ring is not important in controlling the heme reactivity of hemoglobin or of other hemoproteins. However, hydrogen bonding to the metal-bound imidazole can have a powerful influence on heme reactivity.