Involved in the degradation of gentisate (PubMed:10049846). Catalyzes the conversion of gentisate (2,5-dihydroxybenzoate) to maleylpyruvate. Exhibits broad substrate specificities towards alkyl and halogenated gentisates (PubMed:10049846, PubMed:16237038). 2,5-dihydroxybenzoate + O2 = 3-maleylpyruvate + H(+) Completely inhibited by the presence of 5 mM Cu(2+). Partially inhibited with 5 mM Mn(2+), Zn(2+) or EDTA. kcat is 2433 min(-1) with gentisate as substrate. kcat is 3098 min(-1) with 3-methylgentisate as substrate. kcat is 613 min(-1) with 3-bromogentisate as substrate. kcat is 1573 min(-1) with 3-isopropylgentisate as substrate. Optimum pH is around 8.0. Optimum temperature is 50 degrees Celsius. Homotetramer. Shows relatively high basal levels of expression under non-inducing conditions. Induced by aromatic substrates, especially 3-hydroxybenzoate. Knockout mutant can still grow on minimal agar plates containing gentisate as the sole carbon source but GDO activity cannot be detected in uninduced cells. Belongs to the gentisate 1,2-dioxygenase family.