' 

 48 THE PROPERTIES OF PROTEINS 



mixtures. In other words, the mean basic dissociation constant 

 K 6 is increased. The hydrion concentration necessary for the 

 development of iso-electric behaviour is decreased by this 

 increase in K&. Such an effect is actually observed in the 

 results given above for the effect of adding strong acids. 



The so-called iso-electric behaviour culminates in the migra- 

 tion of equal quantities of albumin in both directions, or by 

 symmetrical repulsion, when an electric field is applied. This 

 result, however, only proves an equal volume concentration of 

 positively and negatively charged quantities of protein pro- 

 vided that the electro-positive and electro-negative protein 

 particles transported have the same valency. For, suppose the 

 positive particles are w-valent, and the negative ones mono- 

 valent, then the same weight contains n positive charges, 

 but only one negative charge, so that when one unit of elec- 

 tricity is transferred, the quantity of albumin which migrates 



towards the negative pole is -th of the quantity which goes 



towards the positive pole. The quantity of albumin trans- 

 ported in each direction is the same only when n times as many 

 positive charges are brought by the albumin to the cathode as 

 there are negative charges brought to the anode. 



We can, by this time, follow the main lines of the complex 

 mechanism of the reaction of albumin with strong acids if 

 three principles which are in agreement with all previous 

 investigations are grasped. 



1. When a strong acid is added it reacts with the basic part 



of the albumin A+OH in accordance with the equa- 

 tion, for example : 



A+OH + HC1 > A+C1 + H 2 0. 



If the acid is strong enough, it reacts with further basic 

 valencies of the protein when more acid is added, thus : 



A+C1 + HC1 A++C1 2 , 



forming polyvalent ions. (See the next Chapter.) 



2. Increase in [H>] represses the ionisation of the acid 



portion of the protein A~H with formation of neutral 

 particles, which can, however, react by means of their 

 basic valencies when more acid is added. 



