Light-scattering investigations of the subunit dissociation of human hemoglobin A. Effects of various neutral salts

Abstract

The effectiveness of various salts of the Hofmeister series as dissociating agents for human Hb A tetramers was investigated by light-scattering MW measurements. Dissociation of Hb to half-molecules of .alpha..beta. dimers follows the order of the series dictated predominantly by the sequence of the anions F- < Cl- < Br- < ClO4- < SCN-, I-, with the cations Na+ and K+ having relatively little effect on the observed dissociation. The use of equations derived for predicting the effects of dissociating reagents on the structure of subunit proteins together with Setschenow constants based on the model amino acid data of Nandi and Robinson gave a satisfactory account of the dissociation behavior observed with many of the salts, giving reasonable estimates of the number of amino acids that form the smaller contact area of the .alpha..beta. subunits of Hb shown by the Perutz crystallographic model. The analysis of the dissociation data also extends the utility of the Setschenow constants tested for the characterization of the dissociation behavior of other subunit proteins.