NUCLEIN OR PURINE METABOLISM 877 



The nucleic acid obtained from the pancreas apparently contains 

 one molecule each of /-xylose, phosphoric acid, and guanine, and is 

 therefore spoken of as guanylic acid. In the same way an adenylic 

 acid has been described which contains only adenine, phosphoric acid, 

 and a pentose. 



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 corre- 

 sponding oxy-fatty acid) necessary to the building up of the tissue 

 proteins. The nucleins, on the other hand, can certainly be synthetised 

 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 consider- 

 able 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 there- 

 fore that the nucleic acid is taken up by the cells of the intestinal wall 

 unchanged. Most cells of the body contain nucleases, i.e. ferments 

 capable of hydrolysing nucleic acids and of setting free their purine 



