NUCLEIN OR PURINE METABOLISM 777 



If this is subjected to neutral hydrolysis, it loses the whole of its phosphoric acid and 

 sets free four nucleosides, viz. : guanosine, adenosine, uridine, and cytidine. 



FORMATION OF NUCLEINS IN THE BODY 



In the case of the proteins we saw reason to believe that in the higher 

 animals, at any rate, there was no power of converting one amino-acid into 

 another (with the exception of the lowest member of the series, namely, 

 glycine), and that on this account the food had to contain representatives 

 of every amino-acid (or perhaps of the corresponding oxy-fatty acid) 

 necessary to the building up of the tissue proteins. The nucleins, on the 

 other hand, can certainly be synthesised by the animal. This is shown by 

 the fact that the hen's egg before incubation contains practically no nuclein 

 or purine bases. During incubation tissues are formed, and there is a 

 rapid increase in the number of nuclei, so that the chick just before it is 

 hatched contains a considerable amount of nuclein from which purine bases 

 can be extracted. This nuclein must have been formed by a synthesis 

 from the phospho-proteins and phosphatides (phosphorised fats) which form 

 so prominent a constituent of the egg-yolk, and in the same way the purines 

 must have been formed by a process of synthesis. This synthesis may 

 occur by a conjugation of two urea molecules with the 3-carbon chain 

 which is so prominent a feature in the proximate principles of the body 

 (e.g. in lactic acid, alanine, and all the compound amino-acids of which 

 alanine is a constituent). Methyliminazol, representing one-half of the 

 purine ring, can be formed simply by allowing ammonia and glucose to 

 stand in contact with zinc hydroxide. The power of synthesis of purines 

 possessed by the body must complicate the question of their fate after 

 ingestion, since it is evident that they can either be destroyed and excreted 

 in some other form or that the products of their destruction may be built 

 up into fresh purine or nuclein molecules. In the same way, in the growing 

 child there is a rapid increase in the nuclein of the body, although the only 

 food ingested is milk, which contains but an insignificant amount of nuclein. 



FATE OF NUCLEINS IN THE BODY 



Nucleins and nucleic acids are dissolved by the pancreatic juice, but no 

 digestion of the nucleic acid occurs in the alimentary tract other than by 

 the action of micro-organisms. We must assume therefore that the nucleic 

 acid is taken up by the cells of the intestinal wall unchanged. 



Ingestion of nucleic acid is followed by an increased excretion of uric 

 acid in the urine, so that we regard this substance as the end-product of 

 nuclein metabolism in the body. It is evident that the uric acid of the 

 urine may be derived either from the nucleins of the food or from the 

 nucleins of the tissues of the body, the uric acid in these two cases being 

 spoken of as exogenous and endogenous respectively.' By digestion of 

 nucleic acids with animal tissues or extracts of animal tissues under varying 

 conditions, it is possible to bring about all the changes involved in the 

 conversion of the purine base contained in them into uric acid. In the 



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