title: Analysis of the order of free energy couplings between ligand binding and subunit assembly in human hemoglobin.
abstract: The concept of free energy couplings has been extensively used in studies of the ligand-linked subunit assembly of oligomeric proteins such as human hemoglobin A [cf. Ackers, G. K. (1980) Biophys. J. 32, 331-346]. Recently, the concept of "order" of free energy couplings has been introduced as a description of the number of protein subunits that must be liganded to effect changes in intersubunit interactions [Weber, G. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 7098-7102]. That report utilized the concept of order of free energy couplings to analyze a set of previously published equilibrium constants derived from data pertaining to the chemical equilibrium between oxygen and stripped hemoglobin A [Mills, F. C., Johnson, M. L., & Ackers, G. K. (1976) Biochemistry 15, 5350-5362]. The Weber report claims to have "unequivocally" demonstrated that the coupling between oxygenation and subunit assembly in hemoglobin A is "first order". In the present report, it is demonstrated that free energy couplings of both the first and second order are capable of describing the original oxygen binding data.
mesh_terms: D006441:Hemoglobin A / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D046911:Macromolecular Substances; D008433:Mathematics; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics
chemical_list: D008024:Ligands; D046911:Macromolecular Substances; D006441:Hemoglobin A