Catechol oxidase
![The reduced (Cu(I)-Cu(I)) and native (Cu(II)-Cu(II)) catechol oxidase di-copper active site from the Ipomoea batata crystal structure (PDB: 1BT1, 1BT2).](/Images/godic/202501/03/Catechol_Oxidase_Crystal_Structure_Enzyme_Active_Site0857.png")
![Proposed catalytic cycle of catechol oxidase purified from Ipomoea batata.](/Images/godic/202501/03/lossless-page1-440px-Catechol_Oxidase_Catalytic_Cycle.tif0857.png")
Catechol oxidase is a copper oxidase that contains a type 3 di-copper cofactor and catalyzes the oxidation of ortho-diphenols into ortho-quinones coupled with the reduction of molecular oxygen to water. It is present in a variety of species of plants and fungi including Ipomoea batatas (sweet potato) and Camellia sinensis (Indian tea leaf). Metalloenzymes with type 3 copper centers are characterized by their ability to reversibly bind dioxygen at ambient conditions. In plants, catechol oxidase plays a key role in enzymatic browning by catalyzing the oxidation of catechol to o-quinone in the presence of oxygen, which can rapidly polymerize to form the melanin that grants damaged fruits their dark brown coloration.