772 PHYSIOLOGY 



This body is an indol derivative and consists of a benzene ring and a pyrrol 

 ring having two of their carbon atoms in common. Its formula is 



HC C C.CH 2 CHNH 2 .COOH 



I L 



i.e. it is indol amino-propionic acid. It undergoes, like tyrosine, complete 

 oxidation in the body. On the other hand, a very slight alteration in the 

 molecule renders it incapable of this change. Thus the tryptophane set 

 free by the tryptic digestion of proteins under the influence of the putre- 

 factive bacteria of the intestine may undergo deamination and reduction 

 with the production of indol propionic acid, and this by oxidation may be 

 converted to indol acetic acid. The latter substance by decarboxylation may 

 be converted into skatol, or by oxidation nearer the chain and further loss of 

 carbon dioxide into indol. Of these products of bacterial change, indol 

 acetic acid may be found in the urine, and indol and skatol are oxidised to 

 the corresponding phenols and pass into the urine conjugated either with 

 sulphuric acid or with 'glycuronic acid. Apart, however, from these putre- 

 factive changes due to bacteria, no indol derivatives pass into the urine. 

 The amount of the indol and skatol esters serves therefore merely as an index 

 of bacterial decomposition in the alimentary canal, and gives us no clue to 

 the total tryptophane metabolism of the body. If putrefaction be prevented 

 by the administration of calomel or other intestinal antiseptic these esters 

 may entirely disappear from the urine. On the other hand, the partial 

 obstruction to the onward passage of food, caused by dividing the small 

 intestine in two places a few inches apart and replacing the intervening 

 length of intestine the wrong way round, causes the indican excretion to be 

 increased twenty or thirty fold. Subcutaneous injection of tryptophane in 

 rabbits does not increase the indoxyl and skatoxyl sulphates (urinary 

 indican) in the urine, whereas a considerable increase is brought about by 

 subcutaneous injection of indol. 



The pyrrol ring which occurs in proteins as proline and oxyproline (i.e. 

 pyrrolidine carboxylic acid and oxypyrrolidine carboxylic acid) appears to 

 undergo complete disintegration in the body. The steps in this conversion 

 are unknown, though it is possible that the ring may be unlinked so as to 

 produce from the pyrrol ring amino-valerianic acid, which would then under- 

 go the process of deamination with which we are already familiar. This ring 

 is of interest since it appears to take an important part in the building up of 

 the molecule of haematin, the essential prosthetic group of the haemoglobin 

 molecule. 



Another ring grouping, iminazol, occurs in histidine, which is iminazol 

 a-amino-propionic acid. This too undergoes complete oxidation in the 

 body. It is important to bear in mind that this ring may be produced 

 synthetically by very simple means, i.e. by* the action of zinc oxide and 



