Protein which is posttranslationally modified on a tyrosine residue to form TPQ. This modification of a strictly conserved active-site tyrosine residue proceeds via the hydroxylation of tyrosine to Topa (Trihydroxyphenylalanine) and then to TPQ (Topaquinone). It is a self-processing pathway requiring only the protein, copper and molecular oxygen. TPQ is the redox cofactor of most copper-containing amine oxidases.
