A simple tension-displacement model for hemoglobin cooperativity.

Based on the Perutz view of hemoglobin cooperativity and the methodology of statistical physics, a molecular model for heme-heme interactions is proposed. The motion of the iron atom with respect to the heme plane is assumed to be the important feature of the oxygenation step, and results in an expression for hemoglobin saturation as an explicit function of the internal tension of the hemoglobin molecule. Closure of the equation is obtained with the assumption of linearity between the internal tension and the displacement of the iron atom above the heme plane. All model parameters are physically realizable and are characteristic of the hemoglobin molecule. Finally, the model is capable of discriminating between positive and negative cooperativity.