POLYPEPTim ^ 



53 



peptide chain increases, and the colour is also more intense when the 

 carboxyl group is esterified ; this is especially noticeable in the case of 

 triglycyl-glycine and its ester, the so-called biuret base. The same 

 occurs when the carboxyl group is converted into the acid amide 

 group ; here one of the conditions necessary, as shown by Schiff, is 

 added. 



The polypeptides are attacked by nitrous acid with evolution of 

 nitrogen. Fischer found that the imino group as well as the amino 

 group of leucyl-isoserine and glycyl-leucine was attacked by hydro- 

 chloric acid and sodium nitrite, but Abderhalden and van Slyke, who 

 have tested a large number of polypeptides by van Slyke's method 

 (Part I., p. 69) have found that the amino group only is attacked. The 

 following are some of the data they obtained : 



These values all agree closely with the theoretical values except in 

 the cases where glycine contains the amino group and stands at the com- 

 mencement of the chain. If the values obtained be multiplied by 

 the factor o - 8 the true figure results. A differentiation of the amino 

 and imino groups in the polypeptide molecule is thus possible with 

 nitrous acid. 



The polypeptides are not acted upon by potassium permanganate 



