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. 

 (<:) Peptones, e.g. t fibrinpeptone. 



(d) 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, sulphur, 

 and oxygen, and they possess the following elementary composition : 



C 51-55 per cent. 

 H 7 

 N 15-19 

 S 0-4-2-5 

 O 20-30 

 from which a formula such as 



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, combined 

 with a purine base or a carbohydrate, which substances constitute 

 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. Monoaminomonocarboxylic acids. 



x. 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 B H U NO 2 , or a-aminoisovalerianic acid. 



CH 3 v 



^>CH . CH(NH 2 ) . COOH 



4. Leucine, C 6 H 18 NO 2 , or a-aminoisocaproic acid. 



CH 3 v 



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

 CH 3 / 



