Involved in the degradation of salicylate via a pathway involving coenzyme A derivative. Catalyzes the oxygen-dependent ring fission of gentisate between the carboxyl and proximal hydroxyl groups at positions 1 and 2 of the aromatic ring to form maleylpyruvate. The substrate specificity is strong, since salicylate, catechol, protocatechuic acid, homogenetisate, 2,3-dihydroxybenzoate or 5-aminosalicylate cannot substitute for gentisate in the ring cleavage reaction. 2,5-dihydroxybenzoate + O2 = 3-maleylpyruvate + H(+) By salicylate. Cells lacking this gene accumulate gentisate. Belongs to the gentisate 1,2-dioxygenase family.