BACTERIAL METABOLISM 'WITHIN THE BODY 681 



Ga. R.CH 2 .CHIS T H 2 .COOH -- E.CH 2 . CII^X H 2 -fc C0 2 . 



Carboxylic decomposition of araino acid with the formation 

 of an amin, 



or 



6b. R.CH 2 .CHNH 2 .COOH + H 2 == R.CH 2 CH 2 XH 2 + H.COOH 



Decarboxylation with the formation of formic acid, and an 



amin. * 



H.COOH = C0 2 + H 2 



Formic acid, under the action of formiase, may be decom- 

 posed into carbon dioxid and hydrogen. 



3. Reactions Illustrative of the Decomposition of 

 Proteins by Bacteria 



a. The Decomposition of Tyrosin. Organisms like Bacillus pro- 

 teus act upon proteins in solution, first by an extracellular cleavage of 

 the protein to polypeptids, and probably peptones by the soluble pro- 

 teolytic enzymes they secrete, then decomposing the polypeptids intra- 

 cellularly, according to the reactions indicated. [In the alimentary canal 

 of man, it is probable that the digestive enzymes are largely responsible 

 for the initial cleavage of the protein molecule. The subsequent steps, 

 giving rise to products not formed by the activity of gastro-intestinal 

 enzymes, as indol, are the result of intracellular digestion of the protein 

 fragments by bacteria. 12 ] 



The following steps in the decomposition of tyrosin to paracresol and 

 phenol indicate the theoretical progress of the decomposition of this aniino 

 acid to compounds, as paracresol and phenol, which have no available 

 energy for the organism. In this state they are eliminated from the 

 bacterial cell and appear in the culture medium, or in the alimentary 

 canal. 



Tyrosin Paraoxyphenyl propionic acid 



OH OH 



4 



1. 



i 



CH 2 CHNH 2 COOH +H 2 - CH 2 CH 2 COOH 



"The formation of protein-liquefying enzymes and the production of indol do not 

 take place in cultures of Bacillus proteus containing utilizablo carbohydrate. 



