Review Lecture - Stereochemical mechanism of oxygen transport by haemoglobin

Abstract

Spectroscopic and chemical evidence speak in favour of the iron-oxygen bond being polar. X-ray analysis shows that the oxygen molecule is inclined at an angle of about 115° to the haem plane. Cooperative binding of oxygen by haemoglobin is due to an equilibrium between two alternative structures, which differ in oxygen affinity by the equiva­lent of 3-3.5 kcal/mol. I proposed that in the low affinity structure the globin opposes the movement of the iron atom from its five-coordinated pyramidal geometry in the haem of deoxyhaemoglobin to its six-coordinated planar geometry in the haem of oxyhaemoglobin, while in the high affinity structure this restraint is absent. Recent evidence supporting this mechanism is described.