The third cupredoxin domain of plant Ascorbate oxidase
Ascorbate oxidase catalyzes the oxidation of ascorbic acid to dehydroascorbic acid. This multicopper oxidase (MCO) is found in cucurbitaceous plants such as pumpkin, cucumber, and melon. It can detect levels of ascorbic acid and eliminate it. The biological function of ascorbate oxidase is still not clear. Ascorbate oxidase belongs to MCO family which couple oxidation of substrates with reduction of dioxygen to water. MCOs are capable of oxidizing a vast range of substrates, varying from aromatic compounds to inorganic compounds such as metals. Although the members of this family have diverse functions, majority of them have three cupredoxin domain repeats. The copper ions are bound in several sites: Type 1, Type 2, and/or Type 3. The ensemble of types 2 and 3 copper is called a trinuclear cluster. MCOs oxidize their substrate by accepting electrons at a mononuclear copper center and transferring them to the active site trinuclear copper center. The cupredoxin domain 3 of 3-domain MCOs contains the Type 1 (T1) copper binding site and part the trinuclear copper binding site, which is located at the interface of domains 1 and 3.
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