172 BREAKDOWN OF NITROGENOUS MATERIAL 



concerned has been called "arginine dihydrolase " to distin- 

 guish it from the arginase of liver cells. 



^NHCHj H2NCH2 



I I 



^^2 Arginine ^Hg 



I +2H2O > I +2NH3 + CO2 



CHg dihydrolase CHg 



I I 



CHNH2 CHNH2 



I I 



COOH COOH 



Arginine dihydrolase is possessed by most Streptococci to 

 varying extent. Its function is not clear, as arginine is an 

 essential amino-acid for the organisms which consequently 

 appear to attack one of their essential nutrients. It is possible 

 that these organisms, which carry out a simple Aomolactic 

 fermentation of glucose, depend upon arginine dihydrolase 

 action for the provision of the carbon dioxide which is essential 

 for their growth. 



The production of indole from tryptophan 



In Chap. II various biochemical tests were outlined for 

 the systematic characterisation of bacteria. One of these 

 tests is the formation of indole in protein-containing and 

 protein-digest media by Esch. coli. It has been known 

 from the early days of bacteriology that some organisms, 

 particularly those of the coli group, produce a strongly 

 smelling substance from protein digests, and that this sub- 

 stance reacts with j9-dimethyl-amino-benzaldehyde in alcoholic 

 HCl to produce a pink colour. The substance was known 

 as indole, and Ehrlich worked out a simple appHcation of the 

 colour reaction for testing the production of indole in cultures. 

 In 1901 Hopkins and Cole showed that the precursor of 



