uricase

Uricase, also known as urate oxidase, is an enzyme that catalyzes the oxidation of uric acid to allantoin, using molecular oxygen and producing hydrogen peroxide and carbon dioxide as byproducts. It is found in many bacteria, fungi, and plants and serves to dispose of uric acid in those organisms. The enzymatic reaction can be summarized as uric acid + O2 + H2O → allantoin + CO2 + H2O2.

In humans and other higher primates, the uricase gene is nonfunctional, making humans unable to convert uric acid to allantoin. As a result, uric acid levels are maintained by renal excretion and endogenous production rather than by uricase-mediated degradation.

Uricase has diagnostic and therapeutic relevance. In clinical chemistry, uricase-based assays are used to measure uric acid in serum or urine; the enzyme converts uric acid to a product that, with a peroxidase step, yields a measurable color change proportional to uric acid concentration. Therapeutically, recombinant uricases have been developed to reduce hyperuricemia. Rasburicase is used to prevent tumor lysis–associated hyperuricemia, while pegloticase is a PEGylated form indicated for chronic gout in adults refractory to conventional therapy. Both enzymes lower serum uric acid by converting it to allantoin, which is more soluble and easily excreted.

Immunogenicity is a consideration with non-human uricases. Infusion reactions and hypersensitivity can occur, and rasburicase may cause oxidative stress–related hemolysis in individuals with G6PD deficiency due to hydrogen peroxide production.