EXCRETION 



283 



NH 2 



I 



CO 

 NH 2 



NH— CO 



I I 



CO C— NH. 



CO 



NH— C— NH" 



UREA URIC ACID 



HN— CO 



NH 2 — C C— NH 



II II \CH 



N— C N^ 



GUANINE 

 NH 2 



CO CO— NR 

 NH— CH— NH 



ALLANTOIN 



CH 3 



\ 



CH 3 — N=0 



/ 

 CH 3 



TRIMETHYLAMINE OXIDE 



N=C— NH 2 

 HC C-NR 



N— C 



-N 



/ 



CH 



CO 



ADENINE 

 NH 2 NH 2 



CO COOH CO 

 NH— CH NH 



ALLANTOIC ACID 



Trimethylamine oxide is a nitrogenous base found in marine teleosts, 

 elasmobranchs and in several invertebrate groups, especially molluscs and 

 crustaceans. Levels in blood and tissues of these animals are shown in 

 Table 7.3. The characteristic odour which arises from marine fish after 

 death is due to the liberation of trimethylamine from the oxide as the result 

 of bacterial activity. Trimethylamine oxide is a soluble non-toxic substance 

 with neutral reaction. It forms a considerable proportion of the waste 

 nitrogen excreted by marine teleosts (30% or more), and smaller amounts 

 are excreted by selachians (Table 7.2). Trimethylamine oxide is possibly 

 produced by methylation of ammonia, but the process is poorly under- 

 stood. Mammalian experiments have shown that trimethylamine can be 

 converted into urea (1). 



Creatine and creatinine: creatine (as creatine phosphate) plays an im- 

 portant role in muscle metabolism of vertebrates and also occurs in some 

 protochordates and echinoderms (Chapter 9). It is always present in 

 small amounts in the excreta of vertebrates, and is an important con- 

 stituent of urinary nitrogen in some teleosts (Table 7.2). Some creatine 

 may be converted into creatinine, and both occur in the urine of some 

 species (53). 



Nitrogenous pigments are produced by breakdown of haemochromogens 

 and other substances. The metabolism of haem in vertebrates gives rise 

 to bile pigments which are excreted in the urine and faeces. Little precise 

 information is available about the transformation of nitrogenous pigments 

 among invertebrates. Bile pigments occurring in wandering connective 

 tissue cells of the leech Pontobdella are derived from breakdown of ingested 



