180 



INTERMEDIATE METABOLISM 



originate in the exogenous metabolism of protein. The 

 cystine which is not required for tissue building, at the 

 same time as it loses its NHg groups loses also its two 

 sulphur atoms, which are oxidised and excreted. 



The excretion of neutral sulphur, on the other hand, is 

 hardly influenced by changes in diet. On this account it 

 is considered to be of endogenous origin. The ethereal 

 sulphates are salts of phehyl-sulphuric acid and indoxyl- 

 sulphuric acid. They are formed in the following way :— 



By bacterial decomposition in the intestine, and to a 

 lesser extent in suppurating tissues, tyrosine and phenyl- 

 alanine lose their side-chains and become converted into 

 phenol. By the same process tryptophane becomes con- 

 verted into scatol and indol. Phenol, scatol and indol, 

 all toxic substances, are then absorbed into the blood. 

 Within the body, probably in the hver, they become hnked 

 with sulphuric acid, phenol directly and scatol and indol after 

 oxidation to indoxyl. The effect of this hnkage is to deprive 

 these substances of their toxicity prior to their excretion. 



The above changes may be expressed thus : — 



CHjCHNH.COOH 



/\ 



Tyrosine. 



OH 



Phenol. 



HSO4 

 Phenyl Sulphuric Acid. 



HO 

 HC 



CH 



/\C 



CO OH 



CHNH, HC 



I 



CH, TT HC 



C 

 CH"^ 



CH" NH 



Tryptophane. 



CH 



CH, 

 CH 



'HC 

 HC 



CH WH 



Scatol. 



CH 



/\C 



CH 

 CH 



CH NH 

 Indol. 



CH 



^HC 

 HC 



COH 

 CH 



HC 

 HC 



CH 



/\C 



CHSO, 



CH NH 



Indoxyl. 



\/c\/ 



CH NH 



Indoxyl Sulphuric Acid 



