Light scattering studies of the quaternary structure and subunit dissociation of proteins: The use of hydrophobic solutes and salts as probes

The use of hydrophobic reagents and salts on the molecular weight behavior of subunit proteins, such as the four-chain human and the multichain earthworm hemoglobins, is described in relation to the forces that stabilize their quaternary structure in solution, and the nature and number of amino acids located at the contact areas of their subunits. The equations derived for analysis of light scattering dissociation data are described together with the use of binding and Setschenow constants of the probe molecules or dissociating reagents. For human hemoglobin A the dissociation to half molecules, with several alkylureas, aliphatic acid salts, and some members of the Hofmeister salt series, gave estimates for the number of amino acids at the contact areas of the subunits within the ranges of 19 and 27 amino acid residues suggested by the X-ray crystallographic structure of horse and human hemoglobin.