Figure 6: Structure of phenol hydroxylase from T. cutaneum as determined by X-ray crystallography (PDB code: 1PN0), an enzyme also able to act over hydroquinone. (a) Overall fold showing the structure of the three structural domains and the location of FAD cofactor and phenolic substrate in the catalytic pocket of the enzyme between domains 1 and 2; (b) detailed view of the catalytic pocket, showing the phenolic substrate close to the FAD cofactor; (c) close-up view of the residues involved in the formation of a narrow substrate hole that accommodates monophenols, and located in a flexible protein region that also interacts with the FAD cofactor. The substrate-cofactor pocket is composed of a continuous cavity in the protein body, which is closed by the flavin ring of the FAD cofactor avoiding the escape of the substrate.