The influence of the cation in the precipitation of the proteins of blood by sodium phosphate

The precipitation of the globulins of blood with sodium sulfate at 37°C. 1 indicates the presence of critical zones in the curve of precipitation with increasing concentrations of sodium sulfate. Comparison of the results obtained with sodium sulfate at these zones with other procedures for the precipitation of the proteins of blood, by other salts or acidification, showed similar quantitative results. The critical zones occurred at 10.6 2 , 14.2, 17.7 and 21.3 per cent. of anhydrous sodium sulfate, i. e., the designated quantity of salt dissolved in 100 c.c. of water at 37°C. These values are approximately 0.75, 1.00, 1.25 and 1.50 molar solutions of sodium sulfate. Furthermore, under similar conditions any given concentration of salt will precipitate the same amount of protein. These observations have been extended to other salts and it has so far been found that a similar relationship holds for each salt; after precipitation begins there is a constant difference in the concentration of salt for the succeeding fractions. Precipitation of fibrinogen ends at approximately the concentration of salt found by Lewith 3 for the beginning of the precipitation of euglobulin,—observations which were correlated on the basis of equivalent concentrations by Hofmeister 4 . The difference in concentration between the various fractions is not necessarily the same for all salts, e.g., for magnesium sulfate it is 0.375 mol.

Sodium phosphate at P_H 7.0 compleltes the precipitation of fibrinogen at an approximately molar PO₄ solution and the difference for subsequent fractions is 0.25 mol. By varying the proportions of mono-sodium and di-sodium phosphate to obtain solutions of similar molecular concentration with regard to the PO₄ radicle, but with varying hydrion concentrations, it was found that higher molecular concentrations were required for the precipitation of the various protein fractions.