Figure 22.7 shows pathways of purine catabolism leading to uric acid. As seen in the figure, AMP and GMP can both be hydrolyzed from their phosphates by nucleotidase, ultimately yielding the bases hypoxanthine and xanthine, respectively. Hypoxanthine is converted to xanthine by xanthine oxidase and xanthine is converted to uric acid, also by xanthine oxidase. In addition, AMP can be degraded first in a deamination to form IMP, which loses its phosphate to become inosine. Inosine, in turn, is converted to hyp0xanthine.

Uric acid, the end point of purine degradation in primates, is excreted. Most other animals, however, oxidize uric acid to allantoin, hydrolyze allantoin to allantoic acid and subsequently convert allantoic acid to urea or other possible excretion products, depending on the animal (Figure 22.8).

INTERNET LINKS:

1. Purine Metabolism

2. Purine and Pyrimidine Metabolism