THE CHEMICAL CONSTITUTION OF 

 THE PROTEINS. 



PART II. 



SECTION III. THE SYNTHESIS OF THE PROTEINS. 



Introduction. 



IT has been recognised since the time of Liebig that the protein mole- 

 cule is composed of amino acids, but only during the last decades has 

 it been found that these compounds are so numerous and varied in their 

 chemical composition. 



There are various ways in which we can conceive that the amino 

 acids are combined together in the protein molecule. These were 

 summarised and criticised by F. Hofmeister in 1902 as follows : 



I. The carbon atoms can be linked together directly : 



-cU- 



J 1 



Under these conditions the protein molecule would be a huge 

 branched carbon chain, and its degradation into smaller complexes is 

 difficult to explain, and further, such a decomposition by the action of 

 enzymes, e.g., by trypsin, has not yet been observed. 



II. The carbon atoms can be linked together by an oxygen atom : 



c o c 



I I 



An ether-like combination of the amino acids was suggested by 

 Nasse from the analogy between the hydrolysis of proteins by enzymes 

 and that of the carbohydrates and fats. On account of the small 

 number of hydroxyl groups in the molecules of the amino acids, which 

 is limited to those contained in tyrosine, serine and oxyproline, such a 

 combination can scarcely exist at any rate as the principal method of 

 combination. 



An ester-like combination of the carboxyl group of an amino acid 

 with a hydroxyl group for the same reasons is not possible, nor is the 

 acid anhydride method of combination possible. A further reason 



FT. II. I 



