NUCLEASES AND DEAMIDASES 151 



"nucleases" (cf. Vol. I of this series, p. 128, Chemistry of the 

 Tissues). From recent experiments of London, Schitten- 

 helm and K. Wiener, in which a series of dogs (normal, with- 

 out stomach, without pancreatic juice ligation of the excre- 

 tory ducts of the pancreas, and without pancreas) were fed 

 upon nucleinic acid, it was determined that the cleavage of 

 the nucleinic acid is to be entirely ascribed to the ferments 

 of the intestinal juice. The cleavage always stops at the 

 stage of nucleosides, which undergo no further dissociation 

 in the intestine, the purins remaining in combination with the 

 sugar of the nucleinic acid molecule (as do also the pyri- 

 midin bases) in all experiments. In the lower segments of 

 the bowel the splitting influence of bacteria may be associated 

 with that of the intestinal ferments. 5 The resorption of the 

 purin bodies takes place by way of the blood, not with the 

 lymph. 6 



Cleavage of the nucleinic acids in the animal tissues is 

 undoubtedly a very complicated process. Two kinds of 

 nucleases involved are differentiated: "purinnucleases," 

 which split off the purin bases, and "phosphornucleases," 

 which separate phosphoric acid from the molecule; the 

 nucleosides (combinations of purin bases and carbohy- 

 drate), however, remaining intact. 7 It may be recalled (cf. 

 Vol. I of this series, pp. 123-125, Chemistry of the Tissues) 

 that the carbohydrate group in the nucleinic acid molecule is 

 intercalated between phosphoric acid and the base : 



Phosphoric acid ^ Carbohydrate >. Base. 



Further complication of the situation arises from the fact 

 that deamidization of the purin bases may also take place at 

 this stage, provided they are still in organic combination, in 



5 E. S. London, A. Schittenhelm and K. Wiener (Erlangen and St. Peters- 

 burg), Zeitschr. f. physiol. Chem., 77, 86, 1912. 



6 J. Biberfeld and J. S. Schmid ( Breslau ) , Zeitschr. f . physiol. Chem., 60, 

 292, 1909. 



7 Amberg and W. Jones (Johns Hopkins Univ.), Zeitschr. f. physiol. Chem., 

 75, 407, 1911. 



