InterPro domain: IPR034267

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 [ 1 ]; some studies suggest that it may play a crucial role in cell elongation and enlargement [ 2 ]. In pumpkin, its expression is increased during callus growth, fruit development and seedling elongation [ 3 ].

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 centre and transferring them to the active site trinuclear copper centre. 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 [ 4 ].

1. Ascorbate oxidase is the potential conductor of a symphony of signaling pathways. Plant Signal Behav 8, e23213
2. Regulation of ascorbate oxidase expression in pumpkin by auxin and copper. Plant Physiol. 100, 231-7
3. Marked increase in ascorbate oxidase protein in pumpkin callus by adding copper. Plant Physiol. 88, 656-60
4. Refined crystal structure of ascorbate oxidase at 1.9 A resolution. J. Mol. Biol. 224, 179-205