ALBUMIN : THE ISO-ELECTRIC REACTION 29 



boxylic acids with the corresponding acids of the normal 

 aliphatic series is of the highest interest. Aspartic acid is 

 related to succinic acid in the same way as glycocoll is related 

 to acetic acid. The relationship becomes still clearer by com- 

 parison with the corresponding hydroxy-acids : 



CH 3 COOH -> HO . CH 2 . COOH > NH 2 . CH 2 . COOH 



Acetic acid. Glycollic acid. Glycocoll. 



CH 2 . COOH HO . CH COOH NH 2 . CH . COOH 



CH 2 . COOH CH 2 COOH CH 2 COOH 



Succinic acid. Malic acid. Aspartic acid. 



The introduction of NH 2 into the acetic acid molecule causes 

 a vast decrease in K a , which drops from 1*86 X io~ 5 to 1-8 X 

 io- 10 . On the other hand, on forming the amino-acid from 

 succinic acid the acid dissociation constant rises from 6-7 x 

 io~ 5 to 1-5 x io- 4 . The basic dissociation due to the amino- 

 group in glycocoll and in aspartic acid does not, however, differ 

 greatly in the two cases. If the carboxyl-group in aspartic 

 acid is transformed into an amido-group asparagin is formed, 

 and K a falls by io 5 to about the same order of magnitude as 

 that of the amino-monocarboxylic acids. The basic dissocia- 

 tion is not, however, increased, but remains rather below that 

 of the simple amino-monocarboxylic acids. The basic character 

 of the amino-group introduced is almost completely nullified 

 by the acid amide linkage. 



From these examples it can be seen that alterations in K a and 

 K 6 are very varied and relatively independent of known 

 constitutive alterations. Further, it is impossible to conclude 

 that because two amphoteric electrolytes have the same K a and 

 Kft their constitutions correspond to any great extent. 



In order to understand the alterations in state of the proteins, 

 it is of great importance to have an accurate knowledge of 

 their dissociation when in the iso-electric state. The latter 

 state is indicated by a lack of motion in either direction in 

 the electric field, and shows that an equal number of electro- 

 negative and electro-positive particles are present. The 

 following considerations were originally brought forward by 

 L. Michaelis, and further developed from one point of view by 



