PROTEINS. 63 



by oxidation or hydrolysis, but inasmuch as the hydrolytic proce- 

 dure has been productive of the more satisfactory results, that type 

 of decomposition procedure alone is used at present. This hydrolysis 

 of the protein molecule may be accomplished by acids, alkalis, or 

 superheated steam, and in digestion by the action of the proteolytic 

 enzymes. The character of the decomposition products varies ac- 

 cording to the method utilized in tearing the molecule apart. Bear- 

 ing this in mind, we may say that the decomposition products of 

 proteins include proteases, peptones, peptides, carbon dioxide, am- 

 monia, hydrogen sulphide, and amino acids. These amino acids 

 constitute a long list of important substances which contain nuclei 

 belonging either to the aliphatic, carbocyclic, or heterocyclic series. 

 The list includes, glycocoll, alanine, serins, phenylalanine, tyrosine, 

 cystine, tryptophane, histidine, valine, arginine, leucine, isoleucine, 

 lysine, aspartic acid, glntamic acid, proline, oxyproline, and diamino- 

 trihydroxydodecanoic acid. Of these amino acids, tyrosine and 

 phenylalanine contain carbocyclic nuclei, histidine, proline and tryp- 

 tophane contain heterocyclic nuclei, and the remaining members of 

 the list, as given, contain aliphatic nuclei. The amino acids are pre- 

 eminently the most important class of protein decomposition prod- 

 ucts. These amino acids are all a-amino acids, and, with the 

 exception of glycocoll, are all optically active. Furthermore they 

 are amphoteric substances and consequently are able to form salts 

 with both bases and acids. These properties are inherent in the 

 NH 2 and COOH groups of the amino acids. 



The decomposition products of protein may be grouped as pri- 

 mary and secondary decomposition products. By primary products 

 are meant those which exist as radicals within the protein molecule 

 and which are liberated, upon cleavage of this molecule, with their 

 carbon chains intact and the position of their nitrogen unaltered. 

 The secondary products are those which result from the disintegra- 

 tion of the primary cleavage products. No matter what method 

 is used to decompose a given protein molecule, the primary products 

 are Jargely the same under all conditions. 1 



In the process of hydrolysis the protein molecule is gradually 

 broken down and less complicated aggregates than the original 

 molecule are formed, which are known as proteases, peptones and 

 peptides and which still possess true protein characteristics. Fur- 

 t 1 - T hydrolysis causes the ultimate transformation of these sub- 

 Alkaline hydrolysis yields urea and ornithine which result from arginhie, 

 the product of acid hydrolysis. 



