616 G. SCHMIDT 



According to Keilin and Hartree the quotient C02formed-O2con8umed has the 

 value of 1 with purified uricase preparations which are free of catalase. 

 Crude uricase preparations are always contaminated with catalase, and 

 their action results in an increased respiratory quotient. 



Mechanism of the decarboxylation reaction. Progress in the understanding 

 of uricase action was initiated by three approaches: (1) The direct experi- 

 mental proof for the origin of the carbon dioxide from the 6-C atom of uric 

 acid. This evidence was furnished by Bentley and Xeuberger^^'^ by the en- 

 zymic uricolysis of 6-C^*-labelled uric acid. (2) The experimental separation 

 of uricase action into its oxidation and decarboxylation phases. The feasi- 

 bility of such a separation was first demonstrated in 1929 by Felix, Scheel, 

 and Schuler,^*® who found that, at pH 8.9, the oxygen consumption was 

 much more rapid than the carbon dioxide formation. A further important 

 advance was Klemperer's observation^'*^ (1945) that borate ions have a spe- 

 cific inhibitory effect on the decarboxylation phase and allantoin formation 

 of uricase action. The study of enzymic uricolysis in borate buffers has 

 become an indispensable method for the exploration of the mechanism of 

 uricase action. (3) The oxidation of uric acid with alkaline permanganate 

 which also results in the formation of allantoin is a useful model reaction in 

 the search for the unstable intermediary of the biological formation of 

 allantoin.249-251 



Nature of the unstable intermediary product of the enzymic oxidation of uric 

 acid (see also Chapter 26). Cavalieri and Brown"- found that 1,3-N'^- 

 labelled uric acid yielded an allantoin which was equally labelled in both 

 ureido groups. The same holds true for allantoin isolated from the urine of 

 rats fed with 1 ,3-N^^-labelled uric acid. On the basis of these observations 

 Brown et al}^^ suggested an oxidation product of symmetrical structure as 

 the immediate precursor of allantoin. A similar postulate for the permanga- 

 nate oxidation of uric acid had already been made by Behrend,^^^ who ex- 

 plained by this assumption earlier observations by Fischer and Ach."^ These 

 authors found that permanganate oxidation of 1-methyluric acid and 7- 

 methyluric acid yielded 3-methylallantoin, whereas the oxidation of both 

 3-methyl uric acid and 9-methyluric acid yielded 1-methylallantoin. 



The postulated symmetrical intermediary (Fig. 9) formed during per- 

 manganate oxidation was isolated by Schuler and ReindeF" as the trisilver 



2« F. W. Klemperer, J. Biol. Chem. 160, 111 (1945). 



2" R. Behrend, Ann. 333, 141 (1904). 



"»R. Behrend and R. Schultz, Ann. 366, 21 (1909). 



2" W. Schuler and W. Reindel, Z. physiol. Chem. 208, 248 (1932). 



262 L. F. Cavalieri and G. B. Brown, J. Am. Chem. Soc. 70, 1242 (1948). 



2" G. B. Brown, P. M. Roll, A. A. Plentl, and L. F. Cavalieri, J. Biol. Chem. 172, 



469 (1948). 

 254 E. Fischer and F. Ach, Ber. 32, 2745 (1899). 



