The Solubility of the Plasma Proteins

In a paper from this laboratory, describing the dependence of the solubility of the plasma proteins in concentrated salt solutions on the salt and plasma concentrations (l), we pointed out the advantage of using potassium phosphate as a precipitating salt inasmuch as the salt concentration and pH of such solutions could be varied independently as described by Cohn (2). For the specific purpose of ascertaining the optimum conditions for separating the plasma proteins by single fractional precipitation, we have continued the study of the solubilities of these proteins in concentrated solutions of potassium phosphate and in this paper report data on the effect of pH, temperature, and removal of lipids on the solubility curve of the proteins of horse plasma. Though the dependence of the solubility of protein in salt solutions on pH is clearly established (3, 4), but few data on the quantitative relation between the solubility of the serum proteins in concentrated salt solutions and pH have been presented over the pH range encountered in the salt solutions commonly used for saltingout purposes. Csap6 and von Klobusitzky (5) observed but little effect in the precipitating power of sodium sulfate and sodium chloride solutions on the serum proteins when the pH changed from 4.8 to 7.4. Wu (6), in studying the solubility of serum proteins in sodium sulfate solutions, observed no appreciable effect of pH on their solubility over a pH range of from 5.0 to 9. Howe