Polyphenol oxidase
Enzyme involved in fruit browning / From Wikipedia, the free encyclopedia
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Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in fruit browning, is a tetramer that contains four atoms of copper per molecule.[1]
Catechol oxidase | |||||||||
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Identifiers | |||||||||
EC no. | 1.10.3.2 | ||||||||
Alt. names | Polyphenol oxidase | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
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PPO may accept monophenols and/or o-diphenols as substrates.[2] The enzyme works by catalyzing the o-hydroxylation of monophenol molecules in which the benzene ring contains a single hydroxyl substituent to o-diphenols (phenol molecules containing two hydroxyl substituents at the 1, 2 positions, with no carbon between).[3] It can also further catalyse the oxidation of o-diphenols to produce o-quinones.[4] PPO catalyses the rapid polymerization of o-quinones to produce black, brown or red pigments (polyphenols) that cause fruit browning.
The amino acid tyrosine contains a single phenolic ring that may be oxidised by the action of PPOs to form o-quinone. Hence, PPOs may also be referred to as tyrosinases.[5]
Common foods producing the enzyme include mushrooms (Agaricus bisporus),[6][7] apples (Malus domestica),[8][9] avocados (Persea americana), and lettuce (Lactuca sativa).[10]