PROTEIN METABOLISM 7<>9 



If any creatine undergoes complete oxidation in the body during protein 

 starvation a certain proportion of the urea might be derived in this way. 

 We shall see later that uric acid may possibly also undergo further oxidation 

 with the formation of urea. Even during complete protein starvation some 

 of the urea which is turned out may be the expression of a utilisation of pro- 

 tein through deamination for the energy needs of the body. The active cells 

 are bathed everywhere with a tissue fluid in which proteins form a prepon- 

 derating constituent, and it is possible that, even in the times of greatest 

 protein need, these cells utilise the proteins of their surrounding medium, 

 though in a reduced degree, for the production of energy. In this case the 

 active cell would initiate the utilisation by throwing off that part of the 

 protein molecule, namely, NH 2 , which is useless to the cell as a source of 

 energy, so that deamination would be carried out in the working tissues, and 

 not, as in the rapid formation of urea after a heavy meal, in the liver. 







SULPHUR 



Sulphur occurs in the urine in three forms, namely, as ordinary inorganic 

 sulphates, as ethereal sulphates (indoxyl- and skatoxyl- sulphates), and in an 

 unoxidised condition often termed neutral sulphur. There is no doubt that 

 part of the latter consists of cystine, part of sulphocyanates, and in some 

 animals mercaptan compounds. The excretion of the inorganic sulphates 

 rises pari passu with that of the urea, so that very soon after the throwing 

 off of the NH 2 group there must be also a removal and oxidation of the greater 

 part of the sulphur contained in the cystine group of the protein molecule. 

 So far as regards the metabolism of the body as a whole, the ethereal sulphates 

 may be classed with the inorganic sulphates. They are excreted in varying 

 quantity according to the extent of the decomposition processes which are 

 occurring in the intestine. Under the influence of these processes the trypto- 

 phane, produced in the pancreatic digestion of proteins, is converted into 

 indol and skatol. These two substances after absorption are deprived of 

 their poisonous qualities by oxidation and conjugation with sulphuric acid 

 to form the indoxyl- and skatoxyl- sulphates of the urine, both of which are 

 innocuous. If the processes of putrefaction are increased, as in intestinal 

 obstruction, the relative amount of sulphate appearing in the conjugated 

 form is also increased. On administration of phenol a large proportion of 

 the sulphate appears in the urine conjugated with phenol or with products of 

 its oxidation. If the normal putrefactive processes which go on in the 

 intestine are abolished by the administration of intestinal antiseptics such 

 as naphthalene or calomel, the ethereal sulphates practically disappear 

 from the urine. We cannot therefore regard the absence or diminution of 

 the ethereal sulphates during protein starvation as throwing any liglit on the 

 endogenous protein metabolism. On the other hand, the fact that the 

 neutral sulphur undergoes no decrease suggests that this part of the sulphur 

 output of the organism may be connected with tissue metabolism. 'Further 

 observations on the output of neutral sulphur during fever or wasting diseases 

 are necessary before a definite conclusion can be arrived at on this point. 



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