Purine nucleotide catabolism in rat liver. Certain preliminary aspects of uricase reaction

We investigated the mechanism of action of uricase, which oxidizes uric acid to allantoin, in the rat. Allantoin may decompose chemically to urea and hydantoin, containing the carbons in positions 2 and 8 of the purine ring, respectively. These carbons are derived by formylation, catalyzed by formyltransferase, in two reactions of de novo synthesis. Since uric acid and allantoin are represented in equivalent amounts in the liver, we expected to find identical incorporation of radioactivity in C(2) and C(8) of both compounds after administration of (14)C-formate. In the case of (14)C-allantoin, this was true, but not for (14)C-uric acid extracted from rat liver. We interpret these results through a series of experiments and considerations