ARGININE DIHYDROLASE 171 



SPLITTING OF THE MOLECULE 



Two examples of this type of amino-acid degradation will 

 be discussed. 



Arginine dihydrolase 



The Gram-positive Streptococci and Staphylococci are very 

 exacting in their amino-acid requirements, and this synthetic 

 disability is accompanied by very restricted catabolic activities. 

 The only amino-acid from which these organisms can liberate 

 ammonia rapidly is arginine. The breakdown of arginine is not 

 a simple decarboxylation or deamination, as analysis of the 

 products shows that these are ammonia, carbon dioxide, and 

 ornithine. In mammalian liver we get a somewhat similar 

 breakdown of arginine in which urea is first split from arginine 

 by arginase, and can then be decomposed to ammonia and 

 carbon dioxide by urease: 



Urease 2NH3 

 HN^ .NH2 HgN^ /NH2 > + 



CV C ^^^ CO, 



^NHCHg li H2NCH2 



I ^ .1 



CH2 Arginase Urea ^ll2 



I +H2O > I 



CH2 CH2 



CHNH, CHNH 



COOH COOH 



Arginine Ornithine 



However, there is no evidence of the intermediate formation 

 of urea during the degradation of arginine by Streptococci, 

 and these organisms do not possess urease. The reaction is 

 presumably a direct hydrolysis as shown below, and the enzyme 



