Tyrosine codon corresponds to topa quinone at the active site of copper amine oxidases.

Copper amine oxidase from Hansenula polymorpha: the crystal structure determined at 2.4 å resolution reveals the active conformation

“…CAOs use copper and a modified amino acid sidechain as redox cofactor to achieve substrate deamination and dioxygen reduction. In early studies, CAOs were shown to contain a reactive carbonyl group, leading to suggestions that covalently bound pyridoxal phosphate [33] or pyrroloquinonoline quinone [34,35] were the cofactor [36,37]. It has, however, since been demonstrated that the cofactor is a modified tyrosine designated 2,4,5-trihydroxyphenylalanine, or topaquinone (TPQ) [18,20,36,37].…”

“…In early studies, CAOs were shown to contain a reactive carbonyl group, leading to suggestions that covalently bound pyridoxal phosphate [33] or pyrroloquinonoline quinone [34,35] were the cofactor [36,37]. It has, however, since been demonstrated that the cofactor is a modified tyrosine designated 2,4,5-trihydroxyphenylalanine, or topaquinone (TPQ) [18,20,36,37]. Formation of the TPQ cofactor appears to occur via a self-catalytic mechanism in which a single tyrosine residue is oxidized by protein-bound copper and molecular oxygen [7,38].…”

Crystal structure of a quinoenzyme: copper amine oxidase of Escherichia coli at 2 å resolution

“…The cofactor was initially proposed to be 2,7,9-tricarboxypyrroloquinoline quinone (PQQ) in copper amine oxidases and in several other redox-active enzymes [5]. However, the cofactor was subsequently shown to be the quinone derived from 2,4,5-trihydroxyphenylalanine (TPQ) in bovine serum amine oxidase [6] and other copper amine oxidases [7][8][9]. In the other proposed PQQ-containing enzymes, namely methylamine dehydrogenase and galactose oxidase, the cofactors have since been shown to be tryptophan tryptophylquinone (TTQ) [10] and 3'-S-cysteinyltyrosine [11], respectively.…”

“…These cofactors are all formed by the post-translational modification of one or more amino acid side chains of the polypeptide chain. In the copper amine oxidases, the precursor of TPQ has been shown to be a tyrosine [7] and quinone formation is a self-processing phenomenon requiring only the copper bound in the active site of the enzyme and the presence of oxygen [8,12].…”

The nature of the coordination sites of transition metals in proteins

“…The coppercontaining amine oxides have been well studied by spectroscopic and kinetic methods (Klinman Sz Mu 1994) and comprise one copper atom and one organic cofactor per subunit. The cofactor was initially proposed to be 2,7,9-tricarboxypyrroloquinoline quinone (pqq) (Duine & Jongejan 1989) but was later identified to be the quinone derived from 2,4,5-trihydroxyphenylalanine (tpq) in bovine serum amine oxidase (Janes et al 1990) and in other copper amine oxidases (Mu et al 1992).…”