New mechanistic insights into coupled binuclear copper monooxygenases from the recent elucidation of the ternary intermediate of tyrosinase.

Tyrosinase is the most predominant member of the coupled binuclear copper (CBC) protein family. The recent trapping and spectroscopic definition of the elusive catalytic ternary intermediate (enzyme/O 2 /monophenol) of tyrosinase dictates a monooxygenation mechanism that revises previous proposals and involves cleavage of the μ-η 2 :η 2 -peroxide dicopper(II) O-O bond to accept the phenolic proton, followed by monophenolate coordination to copper concomitant with aromatic hydroxylation by the non-protonated μ-oxo. Here, we compare and contrast previously proposed and current mechanistic models for monophenol monooxygenation of tyrosinase. Next, we discuss how these recent insights provide new opportunities towards uncovering structure-function relationships in CBC enzymes, as well as understanding fundamental principles for O 2 activation and reactivity by bioinorganic active sites.