Dopaquinone hydroxylation through topaquinone cofactor in copper amine oxidases: a simplified chemical model.

A simple model, 4-tert-butyl-1,2-benzoquinone, was chosen to study the hydroxylation step of the tyrosine-derived Dopaquinone residue at the active site of copper amine oxidases in the self-catalytic generation of the Topaquinone cofactor. This hydroxylation step was studied both in the presence and absence of free copper(II), and was found to be dependent on pH value but not on the presence of metal ions. It is therefore proposed that, hydroxide ion and not water should be the true reactive species in this key biosynthetic step of the Topaquinone cofactor, and that the active site Cu2+ is implied, at this point of cofactor biosynthesis, in the quinonisation of Topa rather than in the hydroxylation of Dopaquinone.