I 



28 ELECTRIC CHARGE ON NATURAL SOLUBLE 



order of magnitude. We can conclude, after inspecting their 

 constitutional formulae, that, with the NH 2 -group in the 

 a-position, the length or ramifications of the carbon chain have 

 but little influence on the properties of these amphoteric 

 electrolytes. 



CH 2 (NH 2 ) CH 3 CH 3 CH 3 



COOH CH(NH 2 ) CH 



Glycin. COOH CH 2 



I 



Alanin. CH (NH 2 ) 



COOH 



Leucin. 



The introduction of a methyl group in place of the hydrogen 

 of the amino-group causes a slight weakening both of K a and 

 of K 6 in the case of glycocoll. On the other hand, in the series 

 alanin, phenylalanin, ^>-hydroxyphenylalanin (tyrosin), an 

 obvious increase in the acid character can be seen, while the 

 basic properties are but little affected. 



The formation of a dipeptide from a simple amino-acid results 

 in a large increase of K a (by io 2 ), and a decrease of K 6 (by one 

 power of ten only). The combination of either alanin or leucin 

 with glycin to produce a diglycin produces identical properties 

 in the product. It is improbable that the separation of the 

 amino- and carboxyl-groups, which adjoin in the simple 

 oc-amino-acids, is sufficient to account for the alterations in 

 ionisation, but it is quite possible that the acid character of the 

 pep tide linkage, especially in the lactim form, may play an 

 essential part. This is in agreement with our experience of its 

 function in the formation of protein salts. The distance 

 between the NH 2 and the COOH groups is the same for 

 glycyl-, leucyl-, and alanyl-glycin, while the rest of the carbon 

 chains, of varied length, become branched. The latter, both 

 in these cases and in the simple amino-acids we have con- 

 sidered, appear to have no influence on the dissociation. 



A comparison of the amino-mono- and the amino-di-car- 



