IN ISO-ELECTRIC REACTION 41 



The theory of the iso-electric reaction due to L. Michaelis * 

 implies, as already emphasised, the assumption that only two 

 kinds of ions, A+ and A", are present, arising from the dissocia- 

 tion of OH- or H+ respectively. The following equations then 

 hold good : 



[A^UCH and = [A+] . CQH- 



X X 



J 



At the iso-electric point A+ = A~ and C O H = p-^> so that the 



hydrion concentration is 



Consequently, the hydrion concentration at the iso-electric 

 point should, at a given temperature, be a constant, quite 

 independent of the dilution of the albumin. The work of 

 Michaelis and of Pauli and Samec on electrophoresis, as also 

 that of the two latter on precipitation by alcohol, does actually 

 show that the hydrion concentration is independent of the 

 content of protein over a considerable range (Table 7a). An 

 experimental proof of this rule exists, however, only when 

 acetic acid acetate mixture is used, whereas the theory of the 

 iso-electric reaction was extended by its author to the case of 

 any acid, regarding the hydrion concentration present as alone 

 decisive. Sorensen f has formulated this view as follows : 



" To produce in an aqueous solution of an ampholyte the 

 hydrion concentration corresponding to the iso-electric point, 

 so much acid must be added to it (if K a > K 6 ) that the concentra- 

 tion of acid equals the difference between hydrion and hydroxyl 

 ion concentrations at the iso-electric point. The quantity of acid 

 is therefore independent of the ampholyte concentration, and is the 

 same as the amount required to impart to pure water the hydrion 

 concentration existing at the iso-electric point of the substance in 

 question." L. Michaelis J states quite generally: " If a soluble 

 ampholyte is added to a solution of definite hydrion concentra- 

 tion, it behaves like any acid when the [H-] is less than that at 



* See " Handbuch der Biochem." Supplement, p. 24 ff (Jena, 1913), 

 and S. P. L. Sorensen, Ergebn. der Physiol., 1912, 12, 503. 

 t Ergejbn. der Physiol., 1912, 12, 503. 

 } Biochem. Zeitsch., 1912, 47, 251. 



