Scanning molecular sieve chromatography of interacting protein systems. IV. The difference profile method as applied to the Gibbs-Duhem expression in the analysis of the dimer-tetramer equilibria of oxyhemoglobin A.

The recently-developed large zone difference profile method in scanning molecular sieve chromatography is applied to the analysis of the Gibbs-Duhem expression in the tetramer-dimer equilibrium of human oxyhemoglobin A. The preferential binding term and solvation parameters of the Hofmeister anion phosphate are examined. Results indicate that as the concentration of phosphate ions increase, a hydrated phosphate is formed which enhances the association by perturbing the solvation layer of the hemoglobin molecules. The standard free energy change at a given Hofmeister anion activity of ln Ax = -3.2476 is 9.4 +/- 0.2 kcal/mole. delta G0 at ln Ax = -1.2711 is 10.90 +/- 0.05 kcal/mole, suggesting that approximately 11 kcal are required to dissociate one mole of tetramer into dimer.