146 CHEMISTRY OF THE PROTEIDS CHAP. 



simply as long chains built up of amino-acids linked to one another, 

 for there exist still other connections within the albumin-molecule. 



OTHER MODES OF UNION AMONGST AMINO-ACIDS 



In the substance arginin, the radical guanidin is linked to amino- 

 valerianic acid as an imide and not as an amide, and for this reason 

 it is impossible either to obtain the biuret-reaction or to act on arginin 

 with trypsin, erepsin, or boiling acids. It has already been pointed 

 out that arginin occurs in every albumin and even in the peptones (see 

 pp. 150, 188), and therefore the imino-linking is as widely distributed 

 as is the ammo-grouping (Cohnheim). 



With the exception of the protamins all albumins contain the so- 

 called ' amino-nitrogen. ' A certain percentage of the nitrogen in albumins 

 is always given off as ammonia, whenever the albumin is dissociated, 

 and this nitrogen is co-ordinated with the other dissociation-products, 

 as none of the latter give off nitrogen on being boiled with acids. 

 Schmiedeberg 1 observed that after a slight action of alkalies, a small 

 percentage of nitrogen is given off, and that the remaining albumin is 

 altered only to a slight extent; this remainder he calls 'desamido- 

 albuminic acid.' According to Schiff, 2 nitrous acid exerts an action 

 similar to that of an alkali, and he calls the compound which is left 

 after the splitting off of some of the nitrogen * desaminopeptone.' 



This desaminopeptone does not give a proper biuret-reaction, a 

 fact which is explained by Schiff, Hausmann, 3 and Hofmeister 4 as 

 being due to the destruction of the terminal CONH 2 -groups by the 

 nitrous acid. Paal, 5 however, is of the opinion that amin-remainders 

 are split off, basing this opinion on his investigation into the splitting 

 off of nitrogen when glutin- peptone is treated with nitrous acid. 

 The remaining product, the desaminonitrosopeptone possesses only one 

 half the basicity of the original glutin-peptone. How the amounts 

 of amino-nitrogen vary with the different albumins has already been 

 discussed when dealing with the nitrogen radicals (p. 76), and can 

 be read directly from the tables on p. 81. 



That Levites does not believe in the existence of terminal CO.NH 2 - 

 groups has been pointed out on p. 142. 



The existence of terminal amino-groups is, however, proved by the 



1 0. Schmiedeberg, Arch. f. experimentdle Pathol. u. Pharmak. 39. 1 (1897). 



2 H. Schiff, Ber. d. deutsch. chem. Ges. 29. II. 1354 (1896) ; Liebig's Annalen, 299. 

 264 (1898). 



3 W. Hausmann, Zeitschr.f. physiol. Chem, 27- 95 (1899). 



4 F. Hofmeister, Ergebnisse der Physiologic von Asher u. Spiro, I. 1. 759 (1902). 



5 C. Paal, Ber. d. deutsch. chem. Ges. 29. 1084 (1896). 



