714 



PHYSICAL CHEMISTRY OF THE PROTEINS. I 



or not these are the same or different proteins we shall consider at an- 

 other time from the point of view of their respective solubilities. 



The pseudoglobulin was freed from euglobulin by repeated fractional 

 precipitation with ammonium sulfate. The euglobulin is supposed 

 to be completely precipitated from a solution that is one-third satu- 

 rated with respect to ammonium sulfate, and the pseudoglobulin from 

 a solution that is one-half saturated. In practise it was found neces- 

 sary to adopt the procedure described by Haslam (41). Both precip- 

 itates were collected, redissolved, and again one-third saturated with 

 ammonium sulfate. The filtrate from the reprecipitated euglobulin 

 was then added to the pseudoglobulin fraction, and a precipitate 

 appearing in the pseudoglobulin fraction combined with the 



TABLE III. 



Solubility of Serum Globulin IV a. 



T. = 25.0°=t 0.1°C. 



euglobulin.^^ The pseudoglobulin was reprecipitated thirteen times in 

 preparation IVa, and nine times in preparation V. Serum globulin 

 Va represents a smaller and possibly a better defined fraction. Howe 

 (42) has recently presented additional evidence for the existence of 

 two pseudoglobulin fractions (43, 44, 45); the first precipitated at 

 approximately 0.43 saturated ammonium sulfate. In our experience 

 this fraction represents about three-fourths of all the pseudoglobulin. 



The method that has been used in preparing this globulin as an ammonium 

 compound was first worked out in 1919-20 in collaboration with Professor S. P. L. 

 Sorensen, at the Carlsberg Laboratorium. It involves operations of two kinds. 



^^ The precipitation of proteins by electrolytes is not independent of the protein 

 concentration. 



