FAD-dependent monooxygenase; part of the benzoic acid degradation pathway also known as the protocatechuic acid pathway (Ref.2). Benzoic acid debradation begins with the conversion of benzoic acid into 4-hydroxybenzoic acid through hydroxylation by the benzoate-4-monooxygenase bphA, and its partner NADPH-cytochrome P450 reductase cprA which act as a mediator in electron donation from NADPH (By similarity). 4-Hydroxybenzoic acid is then converted into 3,4-dihydroxybenzoic acid (also called protocatechuic acid) by the p-hydroxybenzoate-m-hydroxylase phhA (Ref.2). Protocatechuic acid is converted into 3-carboxy-cis,cis-muconic acid by the intradiol ring-cleavage dioxygenase prcA, which is further metabolized through the 3-oxoadipate pathway to finally enter the tricarboxylic acid cycle (TCA) (Ref.2). 4-hydroxybenzoate + H(+) + NADH + O2 = 3,4-dihydroxybenzoate + H2O + NAD(+) 4-hydroxybenzoate + H(+) + NADPH + O2 = 3,4-dihydroxybenzoate + H2O + NADP(+) Binds 1 FAD per subunit. Expression is induced in the presence of caffeic acid, p-coumaric acid, p-hydroxybenzoic acid, protocatechuic acid, and benzoic acid. Abolishes growth on benzoic acid, benzaldehyde, benzyl alcohol, p-anisic acid, p-anisyl alcohol, and p-hydroxybenzoic acid; and reduces growth on p-coumaric acid and cinnamic acid. Belongs to the PheA/TfdB FAD monooxygenase family.