14 



NITROGEN METABOLISM 



unknown. In other strains, kynurenine is split by kynuren- 

 inase into alanine and anthranilic acid. The oxidation of the 

 latter to COg proceeds via catechol, m-m-muconic acid, 

 and ^-ketoadipic acid. Whilst the three enzyme systems, 

 tryptophan peroxidase, kynureninase and pyrocatechase, 

 were all highly active in cell-free extracts from organisms 



tryptophan 

 /^\ j|CH2Ch(nH2)cOOH 



form yl 

 k ynurenine 



COOH 



CH.COOH 



I 

 CH.CH 



II 

 HOOC.CH 



muconic acid 



HOOC.CH2CO(CH2)2COOH 



/g-ketoadipic acid 



FIG. 2.1. — Pathways of tryptophan degradation in 

 Pseudomonas spp, 



grown in the presence of tryptophan, extracts from cells 

 grown on asparagine exhibited negligible activity. It is 

 notable that in none of the oxidative reactions could dyes 

 like methylene blue replace O2 as the H-acceptor. The 

 degradation of tryptophan via catechol has been termed the 

 'aromatic pathway' whilst that by way of kynurenic acid is 

 known as the 'quinoline pathway'. Animal tissues degrade 

 tryptophan by the former route. The routes of tryptophan 



