DECOMPOSITION OF PROTEINS 473 



Chemistry of protein hydrolysis. Protein decomposition by micro- 

 organisms includes a group of processes; namely, (1) hydrolysis of 

 proteins to albumoses, peptones and amino acids, (2) deaminization 

 resulting in the formation of ammonia, (3) formation of secondary 

 decomposition products, such as amines, (4) completion of decomposi- 

 tion of proteins involving phenomena of oxidation and reduction with 

 the formation of C0 2 , H 2 0, H 2 S and NH 3 . 



When the proteins are hydrolyzed by acids and alkalies, the resulting 

 products are amino acids and some ammonia. The latter is probably 

 liberated as a result of the action of the acid or alkali on the amide 

 union (CO-NH 2 ) in the protein molecule, and in the case of the 

 alkali treatment as a result of the destruction of arginine. The 

 larger portion of the nitrogen is present, after hydrolysis, in the form 

 of amino groups. However, in the protein molecule, the greater por- 

 tion of the nitrogen is present in imino groups (NH), with the excep- 

 tion of one of the two amino groups of lysine (w group) which exists 

 free. 4 This is also true of a part of the nitrogen in histidine, arginine 

 and tryptophane. This co group of lysine accounts for the entire 

 amount of amino nitrogen found in the native protein molecule 

 on treating with nitrous acid. 5 The a-amino groups, which con- 

 stitute the larger portion of the protein nitrogen, are present only 

 condensed into peptide linkages. On hydrolysis, the free amino nitro- 

 gen increases and the peptide linkages (R— CO-NH — R) become 

 separated into amino and carboxyl groups. The measure of this 

 increase in amino nitrogen can serve as an index of the process of pro- 

 tein hydrolysis. 



Some proteins are easily hydrolyzed, while others are acted upon 

 with great difficulty. This is very important from the point of view 

 of the availability of nitrogen for plant growth. The action of chemi- 

 cal reagents and moist heat will bring about a complete hydrolysis 

 of the proteins to amino acids and ammonia. Proteolytic enzymes 

 usually do not break down the protein molecule completely. Some, 

 like pepsin, split up the protein chain at one or more junctures, with- 



4 Van Slyke, D. D., and Birchard, F. J. The nature of the free amino groups 

 in proteins. Jour. Biol. Chem., 16: 539-547. 1913. 



5 Van Slyke, D. D. The analysis of proteins by determination of the chem- 

 ical groups characteristic of the different amino acids. Jour. Biol. Chem., 10: 

 15-55. 1911; Quantitative determination of alipathic amino groups, Ibid., 12: 

 275-284. 1912; Improvement in the method for analysis of proteins by de- 

 termination of the chemical groups characteristic of the different amino acids. 

 Ibid., 16: 539-547. 1913; 22: 281-285. 1915. 



