Oxygenase component of the salicylate 5-hydroxylase (S5H) multicomponent enzyme system which catalyzes the 5-hydroxylation of salicylate to gentisate. Active only on substrates with a ring-substituted carboxylate group with an adjacent hydroxyl group. Primarily active against salicylate and substituted salicylates, but not against 2-hydroxycinnamate, 3-hydroxycinnamate, 2-hydroxyphenylacetate, 3-hydroxyphenylacetate, 2-hydroxybenzophenone, 1-hydroxy-2-naphthoate, 4-methoxysalicylate or 2-hydroxyacetophenone. H(+) + NADH + O2 + salicylate = 2,5-dihydroxybenzoate + H2O + NAD(+) Binds 1 Fe cation per subunit. Binds 1 [2Fe-2S] cluster per subunit. Aromatic compound metabolism; naphthalene degradation. The salicylate 5-hydroxylase (S5H) multicomponent enzyme system is composed of an electron transfer component and an oxygenase component. The electron transfer component is comprised of a ferredoxin reductase (NagAa) and a ferredoxin (NagAb), and the oxygenase component is formed by a large subunit (NagG) and a small subunit (NagH). Cells lacking this gene are not able to convert salicylate to gentisate. Belongs to the bacterial ring-hydroxylating dioxygenase alpha subunit family.