This model describes tryptophan 5-monooxygenase, a member of the family of tetrameric, biopterin-dependent aromatic amino acid hydroxylases found in metazoans. It is closely related to tetrameric phenylalanine-4-hydroxylase and tyrosine 3-monooxygenase, and more distantly related to the monomeric phenylalanine-4-hydroxylase found in some Gram-negative bacteria. [Energy metabolism, Amino acids and amines]