The oxygenation of hemoglobin as a problem in surface chemistry

Abstract

The reaction of oxygen with hemoglobin is cooperative, and the free energy change that causes the cooperative effect is believed to result from the conformational change in the hemoglobin molecule upon oxygenation. If hemoglobin is considered a colloid, the changes on the molecular level due to oxygenation can be estimated in terms of surface free energy. Because of the large surface area of such a system, small changes in surface free energy can result in significant changes in the total free energy of the system and, therefore, in the equilibrium. Specifically, changes in the surface free energy could contribute to the cooperative nature of the interaction and the variation of the equilibrium constant with pH and ionic strength. The approach outlined in this paper suggests a relatively simple way of estimating the variation of the equilibrium constant in a complex system where changes in surface free energy are significant.