Abstract
AbstractCatechol oxidases are ubiquitous plant enzymes with a dinuclear type‐3 copper center. In the wound‐responsive mechanism of the plant, they catalyze the oxidation of a broad range of o‐diphenols to the corresponding o‐quinones coupled with the reduction of oxygen to water. The crystal structures of catechol oxidase from sweet potato in the resting Cu(II)–Cu(II) state, the reduced Cu(I)–Cu(I) form, and in complex with the inhibitor phenylthiourea were analyzed. The catalytic copper center in a central four‐helix bundle is located in a hydrophobic pocket close to the surface. Both metal sites are coordinated by three histidine ligands. His109, ligated to the CuA site, is covalently linked to Cys92 by an unusual thioether bond. On the basis of biochemical, spectroscopic, and structural data, a catalytic mechanism is proposed in which one of the oxygen atoms of the diphenolic substrate binds to CuB of the oxygenated enzyme. There are close structural relationships of catechol oxidase to different hemocyanins.
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