26 NITROGEN METABOLISM 



acidic environment since activity is not increased by buffer- 

 ing the medium. Nor must it be assumed that glucose is 

 used preferentially as a source of carbon and energy and 

 that in consequence the organisms tend not to synthesize 

 the deaminases. On the contrary, the reduced activity may 

 be a reflection of the lack of essential co-factors since Boyd 

 and Lichstein [9] found that the low serine deaminase 

 activity of a washed suspension of Esch. coli (grown in the 

 presence of glucose) was almost immediately increased by 

 the addition of biotin, adenylic acid, yeast extract or liver 

 extract. 



Having considered the enzymes which deaminate amino- 

 acids, it is now convenient to deal with those which attack 

 X)ther groups in the molecule. 



Arginine dihydrolase 



Washed suspensions of Strep, faecalis, Staph, aureus^ 

 'CI. septicum and CI. sporogenes decompose arginine into 

 ornithine, NH3 and CO 2 : 



C.NH(CH2)3CH(NH2)COOH+2H20 



NH 



=2NH3+C02+NH2(CH2)3CH(NH2)COOH 



Since urea is not attacked by Strep, faecalis, the overall 

 reaction cannot be explained in terms of the splitting of 

 arginine into ornithine and urea by arginase and the subse- 

 quent decomposition of urea by urease. Hills [32] therefore 

 proposed that the enzyme system in Strep, faecalis and 

 Staph, aureus should be known as arginine dihydrolase. 

 Recent work has shown that more than one enzyme is in- 

 volved. The first step in the reaction is the formation of am- 

 monia and citrulline, NH2CONH(CH2)3CH(NH2)COOH, 

 which is then degraded to ornithine by an enzyme system 

 activated by inorganic phosphate, Mg"*""^ or Mn"^"*", and 

 ATP or AMP [38, 52]. Strep, faecalis is exacting towards 

 arginine, and arginine can be replaced by ornithine only if 

 the medium also contains adequate amounts of CO 2 . Carbon 



