Specifically deaminates 8-Oxoguanine (8-oxoG) to uric acid. 8-oxoG is formed via the oxidation of guanine within DNA by reactive oxygen species and leads, if uncorrected, to the incorporation of 8-oxoG:A mismatches and eventually to G:C to T:A transversions. 8-oxoguanine + H(+) + H2O = NH4(+) + urate Binds 1 zinc ion per subunit. kcat is 3.3 sec(-1) with guanine as substrate. kcat is 3.9 sec(-1) with isocytosine as substrate. Purine metabolism. Homodimer. Belongs to the metallo-dependent hydrolases superfamily. ATZ/TRZ family.