Properties of Hemoglobin and Pepsin in Solutions of Urea and Other Amides

The occurrence of manyfold increases in the solubility of both native and denatured proteins in the presence of certain specific dissolved substances has been known since the observations of Spiro (53), Ramsden (49), and others.These large increases in solubility have received no satisfactory explanation, but the lytic effect of one of the most effective of these substances, urea, has been utilized in dissolving, or keeping in solution, denatured proteins (8), and for investigating the solution properties of proteins of low solubility (19,31,72).However, Burk and Greenberg (15) and Burk (13), who measured the osmotic pressures of several proteins at high concentrations by dissolving them in 6.66 M urea, deduced that while the molecular weight of ovalbumin was the same in the mixed solvent as in water the molecular weights of a number of others, including horse hemoglobin, were halved or even further lowered.The change in molecular weight for horse hemoglobin was confirmed by Wu and Yang (72), who showed that ox hemoglobin also dissociates in urea, but that the hemoglobins of sheep and dog do not.Similar changes in molecular weight in urea solutions have been described for myosin (70).Burk has pointed to the consistency of these observations with protein dissociations which occur outside the "pH stability regions" in the ultracentrifugal investigations of Svedberg and his collaborators.