E. J. COHN, J. GROSS, AND O. C. JOHNSON 147 



Proteins can ionize as acids or as bases. As acids they migrate to 

 the anode, as bases to the cathode. The nature of the ionization of 

 the protein can thus be inferred from the direction of its migration. 

 When it does not migrate in either direction the protein exists at its 

 isoelectric point. 



The isoelectric point of certain vegetable proteins was determined 

 by the method of cataphoresis. The juice of the vegetable was 

 placed in a U-tube, between electrodes charged with a potential 

 difference, and the direction of the protein migration determined. 

 The migration of protein during cataphoresis was followed both by 

 determining nitrogen in the arms of the U-tube and by heating the 

 Hquid from the arms and noting in it the appearance of coagulated 

 protein. The technique described by Coehn^ and by MichaeHs^ was 

 so modified as to meet the needs of the present research. 



Unless several precautions are observed in investigating the direc- 

 tion and amount of the migration of protein compounds in an electric 

 field the results are scarcely interpretable. The dipping of electrodes 

 into the protein solution especially compHcates the phenomenon^ 

 since proteins are either precipitated or rendered more soluble at 

 the electrodes.* This is brought about, in part, by the accumulation 

 of H+ and 0H~ ions at the cathode and anode respectively. Land- 

 steiner and Pauli obviated these disturbances by using a three cham- 

 bered vessel in determining the isoelectric point of very pure egg 

 albumin.^ Each chamber contained the protein solution, and migra- 

 tion was detected by determining nitrogen in each after the passage of 

 current. Instead of protein solutions in the end-chambers Michaelis 

 substituted a buffer solution of the same hydrogen ion concentration. 



The particular form of apparatus devised for use in these experi- 

 ments is represented in Fig. 1.^*^ The protein solution was placed 

 below and between the stop-cocks, BB, of a U-tube and above was 



^ Coehn, A., Z. Eledrochem., 1909, xv, 652. 



« Michaelis, L., Biochem. Z., 1909, xvi, 81. 



'' Haas, A. R. C, /. Phys. Chem., 1918, xxii, 520. 



^ Robertson, T. B., /. Phys. Chem., 1911, xv, 179. 



^ Landsteiner, K., and Pauli, W., Verhandl. Kong. inn. Med., 1908, xxv, 571. 



^^ The dimensions of the apparatus are of importance only in calculating 

 movement of protein from the nitrogen concentration before and after cata- 

 phoresis. The volume of liquid contained in each arm was 7.4 cc. and in the 

 central chamber below the arms (including stop-cocks) 13 .4 cc. 



