ENZYMES ATTACKING NUCLEIC ACIDS 



617 



Oh Oh 



HN^ ^C-" \ _ H^ HN^^C^ \ - 2c 



I II co^= = ^=^ I I CO 



OC. 



HN 

 I 

 OC. 



^N' 



^Sc^ 



^C\ 



\, 



CO 



^N 



Uric acid isomer with 

 ionized CH group 



III 



HN- 

 OC. 



H 



.CO 



IV 



End products 



+ HjO' 



End products 



COOH 



I H 



^C^ \ 



OC, 



CO 



\ ^c^ / 



H 

 II 



Fig. 9. Intermediary steps in uricolysis. 



Schuler and Reindel's concept 



Bentley and Neuberger's concept 



salt of hydroxyacetylenediureidocarboxylic acid (I). On heating on a boil- 

 ing water bath for 30 minutes, in 50% acetic acid, the silver salt yields al- 

 lantoin in 50% yield; by heating in alkali under similar conditions, the sym- 

 metric ring compound I is oxidized to uroxanic acid (diureidomalonic acid, 

 II) with opening of both rings. 



Schuler and Reindel reported-^" the isolation of a silver salt identical with 

 that of substance I from digests obtained by enzymic uricolysis. The initial 

 increase of the acidity of such digests also favors the assumption of the in- 

 termediary formation of a carboxyl compound prior to the formation of 

 carbon dioxide and allantoin. 



Bentley and Xeuberger raised two objections to the assumption that hy- 

 droxyacetylenediureidocarboxylic acid (I) would be the intermediary prod- 

 uct of enzymic uricolysis: (1) the transient increases of the light absorptions 

 at 260 and 325 ran during the enzymic uricolysis in phosphate buffers 

 (Praetorius-^^) ; (2) the relatively drastic conditions required for the non- 

 enzymic decarboxylation of I to allantoin. 



255 W Schuler and W. Reindel, Z. physiol. Chem. 215, 258 (1933). 

 "« E. Praetorius, Biochim. et Biophys. Acta 2, 602 (1949). 



