WASTE-PRODUCTS OF THE SULPHUR METABOLISM 561 



is contained in the form of Taurine, which, combined with cholic acid, 

 forms the taurocholic acid fraction of the mixed bile-acids. Taurine 

 is amino-ethyl sulphuric acid, and its relationship to the sulphur- 

 containing amino-acid of the tissue-proteins, Cystine, is shown in the 

 following formulae : 



CH 2 S S CH 2 CH 2 (SO 2 OH) 



CHNH 2 CHNH 2 CH 2 NH 2 



I I 



COOH COOH 



Cystine. Taurine. 



The taurine thus excreted is mainly reabsorbed and either reexcreted 

 as taurocholic acid or else transformed into products which are elim- 

 inated in the urine. It will be observed that the relationship of taurine 

 to cystine is a very simple one, decarboxylation and oxidation of the 

 sulphur serving to convert the cystine into taurine. This being the 

 case it is of very great interest to note that the excretory products to 

 which these compounds give rise are very diverse, for as Salkowski 

 originally showed, and his results have been confirmed and amplified 

 by Schmidt, von Adelung and Watson, the administration of taurine 

 in large doses to man by mouth, or subcutaneous or intravenous 

 injection, leads to a large increase in the Neutral Sulphur output, over 

 eighty per cent, of the taurine being excreted within twenty-four 

 hours in a "neutral" form which Salkowski has identified as Tauro- 

 carbamic Acid. Now the administration of cystine in moderate dosage, 

 or of polypeptides containing cystine, leads to an increase in the inor- 

 ganic sulphates only, and a very large dosage is required to elicit an 

 increase of neutral sulphur. 



The fact that the administration of cystine, whether by mouth or 

 intravenously, results in an increased output of inorganic sulphates 

 suggests that a portion of the endogenous sulphur metabolism may 

 be represented in the inorganic sulphates, for, as we have previously 

 argued in connection with a possible endogenous origin of urea, if the 

 circulating amino-acids stand in equilibrium with the tissue-amino- 

 acids, as the results of Van Slyke indicate, and these latter in equi- 

 librium with the tissue-proteins, then the disintegration-products of 

 tissue-proteins must be the amino-acids themselves, for otherwise 

 protein synthesis would go on indefinitely and unchecked. But the 

 amino-acids, including cystine of course, when once released from 

 the tissues must be thrown into the common supply and undergo their 

 share of exogenous metabolism. Indeed it may be questioned whether 

 the neutral sulphur output really represents the metabolism of cystine 

 in the tissues of the body considered collectively, or whether it does not 

 possibly represent the destruction of a special fraction of the cystine 

 which is converted by the liver into taurine, and a series of products 

 obtained from the sulphur-containing compounds of the nervous 

 system, cartilage, etc., in which sulphur is present in radicals other 

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