NITROGEN METABOLISM 



233 



(6) " Hydrocarbons," 



R.CH2.COOH > RCH3 + CO2 (2 carbon atoms less). 



R.COOH > R.H + CO2 (3 carbon atoms less). 



These products arise by the decarboxylation of the sub- 

 stituted acetic and formic acids produced as above. This 

 type of breakdown appears to occur only with amino- 

 acids like tyrosine and tryptophane, which contain ring 

 structures. Tyrosine gives p-cresol (corresponding to 

 R.CH3) by the action of putrefactive organisms under 

 anaerobic conditions, and phenol (RH) by the same 

 organisms under aerobic conditions : — 



CH3 

 /\ 



I I (p-cresol) 



i I 



OH 



CHa.CH.XHo.COOH 



I 



OH 



OH 



(tyrosine) 



COOH 



(phenol) 



OH OH 



As much as 0-8 gram of phenol per litre may be formed 

 by certain organisms isolated from fseces. 



Tryptophane gives scatole by the anaerobic action of 

 Esch. coll and indole by its aerobic action, but only if 

 sugars are absent from the medium. 



_CH2.C00H ,/ \ CH, 



NH 



CH,.(JH.XH,COOH (indole-acetic acid) 



NH 



(tryptophane) 



COOH 



I II II > I II II 



^\/\ / ^ /\/' 

 ' NH NH 



(^iiiiloli>o;irbo3£:ylir aoiil) (iiulolo) 



