CHAPTER IX 

 BREAKDOWN OF NITROGENOUS MATERIAL 



The synthesis of protein is one of the main reactions involved 

 in the growth of the bacterial cell. In Chap. V we were 

 largely concerned with the nature of the bricks from which the 

 cell builds its protein and with the activation of the enzymes 

 concerned in the building process. The building process often 

 takes place at the expense of complex substances existing in 

 the environment. It is as though we wished to build a 

 laboratory on the site of an apartment; the one structure must 

 be demolished to its constituent units before the new one can 

 be constructed in its place. Consequently the growth of new 

 cells in an environment already utilised by previous growth 

 involves the degradation of the complex proteins, etc., left 

 by the earlier inhabitants, to assimilable material such as 

 amino-acids, ammonia, or even nitrogen, and simple carbon 

 substances. In this chapter we shall be concerned with these 

 breakdown reactions. 



Proteolysis 



Under this heading we group those reactions involved in 

 the hydrolysis of protein to amino-acids. The series of 

 enzymes involved in such breakdown has been studied with 

 great success in animals, and the proteolytic enzymes of the 

 mammalian intestinal tract have been divided into pepsin, 

 trypsin, " erepsin," polypeptidases, peptidases, etc., but 

 comparatively few studies in detail have been made of the 

 corresponding enzymes formed by bacteria. The native 

 protein molecule is too large to enter the bacterial cell, and 

 consequently if the organism is to utilise such molecules it 

 must first excrete extracellular enzymes to start the 

 hydrolysis. The power to excrete such enzymes in quantity 

 is restricted to comparatively few species. Some of the 

 Clostridia, such as CI. histolyticum and CI. sporogenes, excrete 



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