AMINO-ACID CATABOLISM I3 



of carbon and energy, a property which has been widely 

 exploited by Stanier in the elucidation of metabolic path- 

 ways by the technique of 'simultaneous adaptation' [54]. If 

 an organism exhibits little or no detectable activity against 

 a certain substance, and if the inclusion of this substance in 

 its environment evokes, in the absence of cell division, a 

 marked increase in the organism's ability to metabolize that 

 substance, then adaptation is said to have taken place. If an 

 organism can metabolize a particular compound, the hypo- 

 thesis of simultaneous adaptation postulates that it can also 

 metabolize immediately, and at a comparable rate, any sub- 

 stance which is an intermediate in the metabolism of that 

 compound (assuming that the intermediate can pass into the 

 cells). If there is a lag period prior to the rates of utilization 

 becoming comparable, then it may be concluded that the 

 substance cannot be attacked by the existing metabolic 

 systems, in other words, it is not an intermediate, and is only 

 metabolized after adaptation has taken place. From such 

 data it may be possible to deduce the probable route by 

 which a substance is catabolized, but unequivocal proof 

 requires not only direct evidence of formation of the inter- 

 mediates but also isolation of the appropriate enzymes. The 

 aerobic nature of the Pseudomonas spp. means that the 

 overall catabolism of whole cells can be studied mano- 

 metrically in terms of an uptake of O2 , and an example of 

 this technique is provided by the investigations concerned 

 with the degradation of tryptophan [55]. After being grown 

 on, or otherwise adapted to tryptophan, some strains of 

 Pseudomonas are simultaneously adapted to formylkynure- 

 nine, kynurenine, anthranilic acid and catechol; whilst 

 others are adapted to kynurenine and kynurenic acid, but 

 not to anthranilic acid or catechol. Work with cell-free 

 extracts [30] revealed that the pyrrole ring of tryptophan 

 (Fig. 2.1) is first ruptured by a peroxidase-oxidase system 

 in which both H2O2 and Og are involved, and the product, 

 formylkynurenine, is then hydrolysed by formylase into 

 formic acid and kynurenine. In some strains, the pyrrole 

 ring is now reformed, thus producing kynurenic acid, but 

 the route by which this substance is metabolized remains 



