An enzyme from Pseudomonas aeruginosa, Pa0142 (gi vertical bar 9945972), that is able to catalyze the deamination of 8-oxoguanine (8-oxoG) to Uric acid has been identified for the first time. 8-Oxoguanine is formed by the oxidation of guanine residues within DNA by reactive oxygen species, and this lesion results in G:C to T.A transversions. The value of k(cat)/K-m for the deamination of 8-oxoG by Pa0142 at pH 8.0 and 30 degrees C is 2 0 x 10(4) M-1 s(-1). This enzyme can also catalyze the deamination of isocystosine and guanine at rates that are approximately an order of magnitude lower. The three-dimensional structure of a homologous enzyme (gi vertical bar 44264246) from the Sargasso Sea has been determined by X-ray diffraction methods to a resolution of 2.2 angstrom (PDB entry). The enzyme folds as a (beta/alpha)(8) barrel and is a member of the amidohydrolase superfamily with a single zinc in the active site. This enzyme catalyzes the deamination of 8-oxoG with a k(cat)/k(m) value of 2.7 x 105 M-1 s(-1). Computational docking of potential high-energy intermediates I-or the deamination reaction to the X-ray crystal structure suggests that active-site binding of 8-oxoG is facilitated by hydrogen-bond interactions From a conserved glutamine that follows beta-strand with the carbonyl group at C6. a conserved tyrosine that follows beta-strand 2 with N7. and a conserved cysteine residue that follows beta-strand 4 with the carbonyl group at C8. A bioinformatic analysis of available protein sequences suggests that similar to 200 other bacteria possess an enzyme capable of catalyzing the deamination of 8-oxoG.