2 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



X. Derivatives of Proteins : 



(a) Metaproteins, e.g., acid-albumin, alkali-globulin. 



(b) Proteoses, e.g., caseose, albumose, globulose. 



(c) Peptones, e.g., fibrinpeptone. 



(cT) Polypeptides, e.g., glycyl-alanine, leucyl-glutamic acid, 

 a tetrapeptide (2 glycine+i alanine+i tyrosine). 



Except the protamines, the histones and the derivatives of the 

 proteins, all the proteins contain carbon, hydrogen, nitrogen, sul- 

 phur and oxygen, and they possess the following elementary com- 

 position : 



C 51-55 per cent. 



H " 7 



N 15-17 



S 0-4-2-5 



O 20-30 

 from which a formula such as, 



C726H 1174 N 194 S 3 O 214 , 

 which is that of globin, the basis of haemoglobin, can be calculated. 



The phosphoproteins and the nucleoproteins contain also the 

 element phosphorus ; in the former, probably combined directly with 

 one of the constituents of the protein molecule ; in the latter, com- 

 bined with a purine base or a carbohydrate, which substances con- 

 stitute nucleic acid. 



Investigations upon their chemical constitution have been carried 

 on now for nearly a century, but it is only during the last ten years 

 that, by the work of Emil Fischer and his pupils, any clear view has 

 really been obtained of their actual constitution. The main result of 

 these investigations is that the protein molecule is built up of a series 

 of amino acids, which form the basis of their composition, and of 

 which the following have been definitely determined : 



A. Mono-aminomonocarboxylic acids. 



1. Glycine, C 2 H 5 NO 2 , or amino-acetic acid. 



CH 2 .(NH 2 ).COOH 



2. Alanine, C 3 H 7 NO 2 , or a-aminopropionic acid. 



CH 3 .CH(NH 2 ).COOH 



3. Valine, C 5 H U NO 2 , or a-aminoisovalerianic acid. 



CH . CH(NH 2 ) . COOH 

 CH 3 / 



4. Leucine, C 6 H 13 NO 2 , or o-aminoisocaproic acid. 

 CH 3 \ 



)CH . CH 2 . CH(NH 2 ) . COOH 

 CH,/ 



