416 BACTERIOLOGICAL CHEMISTRY 



or to acyl- or nitro -proteins (which have strong pokir 

 groups). 



The amino groups of proteins may be altered in other 

 ways. Hopkins and Wormall treated proteins with phenyl 



isocyanate, <^ \N=C = 0, , which reacts with amino 



groups to give phenylureides or substituted ureas : — 

 R.CH2.NH2 R.CH2.NH 



+ > ^CO 



C6H5N = C = CeHgNH 



The protein-phenylureides were found to have lost the 

 specificity of the original proteins and to have acquired 

 a new one due to the phenylureide group. It was found 

 that the precipitin reactions were inhibited by lysine 

 phenylureide as hapten, indicating that the amino-acid 

 lysine, NH2.CH2.(CH2)3CH.COOH, is involved in the 



I 



NH2 

 formation of the protein phenylureide derivatives. 



Isocyanate derivatives have been used for the intro- 

 duction of other determinants into proteins. For instance 

 the isocyanate derivative of histamine can be made by 

 treating histamine with carbonyl chloride, and then 

 coupled with proteins to give antigens : — ■ 



CH==C.CH,.CH.,.NH2 CH==C.CH,.CH,.N = C = 



i I " " > I I " " 



N NH + COCI2 N NH protein 



CH CH 



(Histamine) ( j3-5-imidazolylethyl isocyanate ) 



CH==C.CHo.CH,.N =CO.NH 



I I " " I 



N NH Protein 



CH 

 The coupling probably occurs through the free terminal 



