Enzymatic Uricolysis and Its Use in Therapy

Abstract

Uric acid is the end product of purine metabolism in some species including man and not in others. In birds and reptiles for example, it is the final metabolite of protein as well as purine degradation. In those organisms in which uric acid is not the terminal excretory product of purine metabolism, the molecule is oxidized to allantoin by the enzyme, urate: O₂-oxidoreductase, also called urate oxidase or uricase (Fig. 1). This enzyme which opens the six-membered ring in the purine molecule, is found in various microorganisms, plants, and the livers and kidneys of most animals. In mammals allantoin is generally the major end product of purine metabolism, but in nonmammalian species there is further metabolism of allantoin. Amphibia and te-leost fishes convert allantoin to allantoic acid through the action of the enzyme, allantoinase. The latter opens the five-membered purine ring. Nonteleost fishes contain the enzyme allantoicase which breaks down allantoic acid into urea and glyoxylic acid. Finally, some invertebrates are known to convert urea to ammonia and carbon dioxide through the action of urease.