BIOSYNTHESIS OF PURINES AND PYRIMIDINES 279 



Reaction 1 



O c 



II H CO, 



\j^'^^-^^ decomposition \j^/ ^^^ Y NHj 



H H H H 



Uric acid Allantoin Glyoxylic 



acid 



COOH 



I 4 5 



CH=N-NH-C0-NH2 + 30 *- HCOOH + Nj + 2CO2 + NH, 



4 



Reaction 2 



O 



II H II 



/C^ /N 7NH2 X. 1NH2 



I2 4 «/C=0 -— ^8C=0+ I2 J — — *2C = + 3C02 



o=c' 3 'a 9/ "^' I o=c. 3J.c=o pi^^^ I 



^N-^ ^N 9NH, ^N-^ 3NH, 



Uric acid Alloxan 



Fig. 1. Degradation of uric acid according to Buchanan et al.^^ 



labeled substances were administered to pigeons and the uric acid subse- 

 quently isolated from the excreta. The uric acid was degraded by previously 

 known reactions and the distribution of the isotope within the molecule 

 determined for each precursor given. 



Because of the extreme importance of the degradations in experiments 

 of this type, both here and in the work discussed below, outlines of the 

 degradative procedures are given. The scheme for the degradation of uric 

 acid is represented in Fig. 1. 



In the first reaction uric acid was oxidized by the procedure of Edson 

 et al}^ to allantoin and CO2 (carbon 6), and the allantoin subsequently 

 decomposed to yield urea and glyoxylic acid. Glyoxylic acid was isolated 

 as the semicarbazone and the latter oxidized to give formic acid (carbon 4) 

 and CO2 (carbon 5). 



In the second reaction the method of Liebig and Wohler^^ was used to 

 oxidize uric acid to alloxan and urea (carbon 8) and the alloxan degraded 

 to CO2 and urea (carbon 2). A combination of the two reactions permits 

 isolation and isotope analysis of each carbon atom from uric acid. 



The results of such degradations after administration of C^^Oo , HC'^- 

 OOH, NHsCHoC^^'OOH, dl-CHsCHOHCi^OOH, and dl-Ci^HsC'^HOH- 

 COOH are summarized in Table I. CO2 is utilized mainly for the synthesis 



15 J. C. Sonne, J. M. Buchanan, and A. M. Delluva, J. Biol. Chem. 173, 69 (1948). 

 i« J. M. Buchanan, J. C. Sonne, and A. M. Delluva, J. Biol. Chem. 173, 81 (1948). 

 "J. Liebig and F. Wohler, Ann. 26, 259, 262, .312 (1838). 



