HpaB Swiss:Q57160 encodes part of the 4-hydroxyphenylacetate 3-hydroxylase from Escherichia coli [2]. HpaB is part of a heterodimeric enzyme that also requires HpaC. The enzyme is NADH-dependent and uses FAD as the redox chromophore. This family also includes PvcC Swiss:O30372 may play a role in one of the proposed hydroxylation steps of pyoverdine chromophore biosynthesis [1].

1: The pvc gene cluster of Pseudomonas aeruginosa: role in synthesis of the pyoverdine chromophore and regulation by PtxR and PvdS. Stintzi A, Johnson Z, Stonehouse M, Ochsner U, Meyer JM, Vasil ML, Poole K; J Bacteriol 1999;181:4118-4124. PMID:10383985

2: Molecular characterization of 4-hydroxyphenylacetate 3-hydroxylase of Escherichia coli. A two-protein component enzyme. Prieto MA, Garcia JL; J Biol Chem 1994;269:22823-22829. PMID:8077235