Polyphenol oxidase

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Polyphenol oxidase (PPO) enzymes catalyse the o-hydroxylation of monophenols (phenol molecules in which the benzene ring contains a single hydroxyl substituent) to o-diphenols (phenol molecules containing two hydroxyl substituents). They can also further catalyse the oxidation of o-diphenols to produce o-quinones. It is the rapid polymerisation of o-quinones to produce black, brown or red pigments (polyphenols) that is the cause of fruit browning. The amino acid tyrosine contains a single phenolic ring that may be oxidised by the action of PPOs to form o-quinone. Consequently PPOs may also be referred to as tyrosinases.[1]

Enzyme nomenclature differentiates between monophenol oxidase enzymes (tyrosinases) and o-diphenol:oxygen oxidoreductase enzymes (catechol oxidases). Therefore please refer to the tyrosinase and catechol oxidase articles for more information on polyphenol oxidase enzymes.

References

  1. Mayer, AM (2006). "Polyphenol oxidases in plants and fungi: Going places? A review". Phytochemistry. 67: 2318–2331. PMID 16973188.

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