Studies on the Chemistry of Hemoglobin

Abstract The ability of several salt solutions to dissociate the tetrameric form of the hemoglobin molecule into dimers has been studied by measuring the osmotic pressure of solutions of hemoglobin. Under most circumstances, the dissociation reactions had the normal dependence on concentration of hemoglobin, and thus values of the dissociation constants could be estimated. In all the solvents studied here, the sequence of decreasing stability of the tetramer was deoxyhemoglobin g CO hemoglobin g oxyhemoglobin ≅ cyanmethemoglobin. This result was interpreted as providing further evidence for differences in conformation, not only between the liganded hemoglobins and deoxyhemoglobin, but also among the various liganded hemoglobins. Similar studies done with iodoacetamide-treated and N-ethylmaleimide-treated hemoglobins indicated that the latter derivative differs in conformation from normal hemoglobin whereas the former does not, by these criteria. Finally, the ability of the various salts to promote dissociation did not depend only on their contribution to the ionic strength of the solvent but also, and in some cases in large part, depended on specific interactions between the salt ions and the protein molecules. The order of effectiveness of the salts in dissociating the hemoglobin tetramers was NaI g guanidinium chloride g NaClO4 g MgCl2 g NaCl ≅ CH3COONa.