66 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Roxas suggested that the mechanism of the reaction was : 

 (i) with histidine: 



H-C 



O HC-R or 



CH CH 



COOH 



(2) with arginine : 

 NH 



CH 



Nil 



H N C N CH, CH CH, 



I 



11 



C 



11 



H-fN CH COOH 

 H 



(3) with tryptophan : 



C CHj-CH-COOH 



HC-E 



C-CH-.-CH-COOH 



N 



NH 



These possible condensation products can explain the formation of 

 pyridine from melanin or humin : 



R-f CH- - C - J N 



I 



NH 



CH 



NH 



CHl COOH 



COOH 



Gortner [1916] showed that the aldehydes, furfural, benzaldehyde 

 and formaldehyde reacted on boiling with hydrochloric acid in a way 

 similar to carbohydrates, and in presence of amino acids the humin 

 nitrogen was large. The humin was mostly insoluble in acid except 

 in the case of tryosine and formaldehyde. It appears that the reaction 

 consists in the formation of furfural from carbohydrate and that humin 

 arises by the condensation or decomposition of furfural together with 

 nitrogen from amino acids if these be present in the solution. 



The loss of products is considerably greater than the quantity of 

 "humin," which generally amounts to 1-2 percent, of the protein. A 

 loss, which cannot be estimated, is represented by the soluble brown 

 pigment which colours the solution. 



