Provided are a 4-ureido-5-carboxyl-imidazole-amide hydrolase and use thereof, particularly use in the treatment of gout.

Provided are a xanthine amide hydrolase and the use thereof, particularly the use thereof for treating gout.

Provided are a uricase activator and a uricase activation method which are capable of highly activating uricase. Also provided are a uric acid measurement reagent and a uric acid measurement method which have a wide measurable concentration range. Further provided are a uricase activator comprising hydroxyisourate hydrolase, and a uric acid measurement reagent for use in measuring a uric acid concentration in a sample collected from a living body, comprising uricase and hydroxyisourate.