520 HEMOLYTIC SENSITIZER AND RED BLOOD CELLS 



to ionization. On the alkaline side of the isoelectric point they ionize 

 as acids, on the acid side as bases ; at the isoelectric point the ionization 

 is at a minimum. It is evident that the combination of sensitizer 

 and cells is related intimately to the ionization of the immune body. 

 The curves showing the fraction of sensitizer free in solution in a 

 salt-free medium follow closely the curves given by Sorenson,^^ after 

 Michaelis,^^ to represent the degree of ionization of an amphoteric 

 electrolyte. The ionized fraction of the sensitizer, both as anion 

 and as cation, corresponds with that fraction which is uncombined 

 with cells, so that we may conclude that the cells combine only with 

 the undissociated molecules of sensitizer. 



The ionization of the cells appears not to be a factor in their com- 

 bination with sensitizer. There is no inflection in the curves at pH 

 4.6, the isoelectric point of the cells. At pH 5.3, the reaction at 

 which the maximal amount of sensitizer is combined, the cells are 

 considerably ionized as is demonstrated in the curve showing their 

 rate of movement in the electric field. ^'^ 



On the alkaline side of the isoelectric point proteins combine only 

 with cations.^" In the presence of NaCl, a Na salt could be formed 

 therefore with the immune body at reactions more alkahne than 

 pH 5.3. If this salt had a small dissociation constant, so that only 

 a small concentration of ampholyte anion could exist in the presence 

 of Na without combining to form undissociated salt, the degree of 

 ionization of the ampholyte would be represented by such a curve 

 (Michaelis^O ^s that showing the proportion of sensitizer uncombined 

 in the presence of NaCl. While we possess no information as to 

 the degree of dissociation of such a Na sensitizer salt, the effect of 

 NaCl is at least suggestive of a depression in the ionization of the 

 sensitizer with combination between the cells and all undissociated 

 molecules of sensitizer, either pure or united with cation to form a 

 salt. 



28 Sorenson, S. P. L., Ergebn. Physiol., 1912, xii, 393. 

 29Michaelis, L., Biochem. Z., 1911, xxxiii, 182. 



30 Loeb, J., J. Gen. Physiol., 1918-19, i, 39, 237, 363, 483, 559. 



31 Michalis, L., Biochem. Z., 1920, ciii, 225. 



