756 CHARGE OF ISOELECTRIC PROTEIN BY IONS 



In these experiments the hydrogen ion concentrations of the inside 

 and outside solutions were measured and the writer begs leave to 

 give these results (Tables VIII, IX, and X), since they prove once 

 more that the p.d. between a solution of gelatin chloride and an 

 outside solution across a collodion membrane is determined by the 

 difference in the pH in the inside and outside solutions, as the Donnan 

 theory demands. In these experiments the influence of the three 

 salts on the osmotic pressure of the gelatin chloride solutions was 

 also measured and the results are given in Fig. 2 showing that the 

 osmotic pressure of a gelatin chloride solution of pH 3.0 is influenced 

 only by the anion but not by the cation of the salt, since the effect 

 of the three salts on the osmotic pressure of the solution is exactly 

 the same when plotted over the concentration of the CI ions. At 

 this pH, therefore, the La does not increase the osmotic pressure of 

 gelatin chloride solutions. 



These observations support the idea that trivalent and tetravalent 

 ions are able to transfer their charge to isoelectric protein by causing 

 the protein to be ionized; probably in such a way that the trivalent 

 or tetravalent ion is part of a complex protein ion. 



SUMMARY AND CONCLUSIONS. 



1. Experiments on anomalous osmosis suggested that salts with 

 trivalent cations, e.g. LaCls, caused isoelectric gelatin to be positively 

 charged, and salts with tetravalent anions, e.g. Na4Fe(CN)6, caused 

 isoelectric gelatin to be negatively charged. In this paper direct 

 measurements of the p.d. between gels of isoelectric gelatin and 

 an aqueous solution as well as between solutions of isoelectric gelatin 

 in a collodion bag and an aqueous solution are published which show 

 that this suggestion was correct. 



2. Experiments on anomalous osmosis suggested that salts like 

 MgCl2, CaCl2, NaCl, LiCl, or Na2S04 produce no charge on isoelectric 

 gelatin and it is shown in this paper that direct measurements of the 

 P.D. support this suggestion. 



3. The question arose as to the nature of the mechanism by which 

 trivalent and tetravalent ions cause the charge of isoelectric proteins. 

 It is shown that salts with such ions act on isoelectric gelatin in a way 



