152 PHYSIOLOGY OF PURIN METABOLISM 



such manner that, according to Schittenhelm, 8 deamidization 

 may involve either free or fixed purin bodies ; and for that 

 reason it is essential to distinguish between purin- 

 deamidases and nudeosiddeamidases. 



It may be seen that in the catabolism of the purin bases 

 included in the nucleinic acid molecule into uric acid a great 

 many different possibilities enter, and that we must assume 

 a coordination of nucleases and nucleoside-splitting fer- 

 ments, of purin-deamidases and nudeosiddeamidases, as 

 well as a number of oxidases. According to Levene and 

 Medigreceanu 9 the nucleinic acids are made up of nucleo- 

 tids, a type of which, according to these authors, may be seen 

 in guanylic acid (Vol. I of this series, pp. 125-128, Chemistry 

 of the Tissues), to which they ascribe the simple constitution 

 of phosphoric acid-pentose-guanin. They then differentiate 

 in the fermentation-cleavage of nucleinic acids between 

 nucleinases, which split up the nucleinic acid molecule into 

 nucleotids, and nucleotidases, which in turn catabolize the 

 nucleotids. 



What an enormous amount of work is still to be accom- 

 plished before we can be in position to clearly define the 

 physiological and pathological influence of any one of these 

 factors ! As a matter of fact this is only the beginning of 

 the difficulty. 



Nuclear Destruction and Urinary Purins. The next 

 question is that of the origin of the endogenous and exog- 

 enous urinary purins, about which it is safe to say that 

 veritable rivers of ink have run dry in advancing to a point 

 where (and this is always a good sign) the matter can be 

 properly stated in a few words. At present we know that 

 the exogenous portion of the urinary purins depends in 

 mammals upon the quantity of free or combined purins in 

 the food, bearing in mind moreover the further conversion of 



A. Schittenhelm and K. Wiener (Erlangen), Zeitschr. f. physiol. Chem., 

 77, 77, 1912. 



P. A. Levene and F. Medigreceanu (Rockefeller Instit., New York), Jour, 

 of Biol. Chem., 9, 65, 375, 389, 1911. 



