322 PROTEINS 



base with pentavalent nitrogen, which is able to react with 

 acids to form salts of the type of R=N'C1. 



This assumption explains the reason why albumen is not 

 precipitated by sodium phosphomolybdate until a little acid 

 has been added, for if albumen in neutral solution is a 

 pseudo-base, it would only be converted into a true base 

 capable of being precipitated by sodium phosphomolybdate 

 after the addition of acid. 



For a further account of the connexion between pseudo- 

 acids or bases and amphoteric electrolytes, see Zadwidzki* 

 and HantzscLf 



THE DECOMPOSITION PRODUCTS OF THE PROTEINS. 



The most direct way of obtaining an insight into the 

 probable groups or groupings which occur in the molecule of 

 some complex substance, is to break it up into simpler ones, 

 whose constitution is already known, or may be determined 

 with comparative ease. This is the method which has been 

 employed to elucidate the very complex structure of the pro- 

 teins. 



Various processes have been employed for breaking down 

 the protein molecule, such as acid hydrolysis, fusion with 

 alkalis, the action of enzymes or putrefactive bacteria, oxida- 

 tion, etc. As a result of all these various methods, a number 

 of simple compounds have been obtained, which fall primarily 

 into two main groups : 



1. Biuretic derivatives, such as albumoses, peptones, etc., 

 which are still very complex substances, but have, at any rate, 

 a lower molecular weight than the original unaltered protein. 

 These substances all give the Biuret reaction. 



2. Abiuretic derivatives. In this group of cleavage pro- 

 ducts, which give no Biuret reaction, are included the various 

 amino acids. 



By an amino acid is meant an acid in which one or more 

 of the hydrogen atoms other than the carboxylic hydrogen 

 are replaced by the amino group NH 2 . Thus acetic acid 

 CH 3 COOH gives rise to the amino acid known as glycine 

 CH 2 V NH 2 COOH. Theoretically it should be possible to re- 



* Zadwidzki : " Ber. deut. chem. Gesells.," 1903, 36, 3325 ; 1904, 37, 153. 

 t Hantzsch: " Ber. deut. chem. Gesells.," 1906, 39, 3149. 



