HO CHEMISTRY OF THE PROTEIDS CHAP. 



little NH 2 is present in albumins, judging by the amount of the 

 nitrogen which is split off and the ease with which the biuret- 

 reaction can be prevented on subjecting albumins to the action of 

 nitrous acid. 



Although albumin treated with nitrous acid gives negative results 

 with the biuret- reaction because of the disappearance of terminal 

 CO NH 2 or OS . NH 2 or - C(NH) . NH 2 or CH 2 . NH 2 radicals 

 (Schiff), 1 it is easy to get once more positive results by hydrolising the 

 albumin, which had been treated by nitrous acid, into its dissociation- 

 products, as hereby NH groups become converted into NH 2 groups. 



Hofmeister illustrated his theory by the following example in 

 which leucin and glutaminic acid are linked together : 

 ^ 



COU NH CH CO ; NH CH CO-4 NH 



I I 



C 4 H 9 (CH 2 ) 2 



CO. OH 



Leucin. Glutaminic acid. 



In this compound the radical CH NH 



CO NH 



occurs, which is. also met with in the following compounds, which give 

 the biuret reaction, namely, 



CH 2 NH 2 CH 2 NH(CH 3 ) CO . NH 2 



CO NH 2 CO NH 2 CH . NH 2 



CH 2 

 CO. 



NH 2 



Glycinamide (Schiff). Sarcosin-araide (Schiff). Aspartic-acid-amide (Fischer). 



Hofmeister's sound theory has been confirmed by the synthetic 

 researches of E. Fisher and Curtius, explained in the last chapter, for 

 there cannot be any doubt that ordinary amino-acids are linked up 

 to form neutral imino-compounds. Other methods of linking up 

 exist also in albumins, but these will be discussed later, see p. 146, 

 after the phenomena which are explainable on the imine-linking have 

 been gone into. 



1 H. Schiff, Ber. d. deutsch. chem. Ges. 29. 298, 3O. 2449 ; and Ldebig's Annalen, 

 299. 236, and 319. 300 (see p. 142 of this book). 



