Uricase purine oxidation

Uric acid is one of the principal products of purine metabolism in man 12 13). However, in many other organisms further oxidative degradation of the purine molecule occurs. One of the most important enzymes involved in uric acid oxidation is uricase, which has been studied to some extent in vitro. 

Purines and pyrimidines in excess of cellular requirements can be degraded. The extent of degradation depends on the organism. Humans cannot degrade purines beyond uric acid because we lack the enzyme uricase, which splits the purine ring to form allantoin. In humans excess AMP is deaminated to IMP by the action of a specific deaminase. IMP is then hydrolyzed by 5 -nucleotidase to form inosine. Inosine and guanine are oxidized to urate as follows ... 

Uricolysis oxidation and decarboxylation of uric acid to allantoin, catalysed by uricase as part of aerobic Purine degradation (see). 

Uricase. Many organisms, including humans, excrete uric acid as the end-product of purine metabolism. Most other mammals, however, oxidize uric acid further. The enzyme uricase has been known for over 60 years, but the nature of the reaction catalyzed is still uncertain. The enzyme has been purified in many laboratories, but until recently was... 

The degradation of purines in ammonotelic animals and in some ureo-telic animals proceeds to ammonia and urea, respectively. The oxypurines, hypoxanthine and xanthine, are oxidized to uric acid which is in turn oxidized, under the influence of uricase, to allantoin. Hydrolysis of allantoin proceeds in two stages to yield allantoic acid, and finally urea and gly-oxylic acid. In ammonotelic animals urease cleaves the urea into carbon dioxide and ammonia. 

Aerobic transformation of uric acid to allantoin (equation 119) is catalyzed by uricase, an enzyme widely distributed throughout the phylogenetic scale, which participates in the final degradation of purines (246,472). It catalyzes oxidation of uric acid only (396) substituted uric acids are not attacked. The course of oxidation is complex, the number of products and their relative proportions being dependent upon conditions of reaction. A summary of these reactions is given in Figure 33 (36,43,96,130-132,181,592). 

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