Enzyme involved in fruit browning
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]
PPO may accept monophenols and/or o -diphenols[ 2] o -hydroxylation of monophenol molecules in which the benzene ring contains a single hydroxyl substituent to o -diphenolsphenol molecules containing two hydroxyl substituents at the 1, 2 positions, with no carbon between).[ 3] oxidation of o -diphenols to produce o -quinones[ 4] 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 lettuce (Lactuca sativa [ 10]
^ "Polyphenol Oxidase" . Worthington Enzyme Manual. Retrieved 13 September 2011 .^ McLarin, Mark-Anthony; Leung, Ivanhoe K. H. (2020). "Substrate Specificity of Polyphenol Oxidase". Crit. Rev. Biochem. Mol. Biol. 55 (3): 274–308. doi :10.1080/10409238.2020.1768209 . PMID 32441137 . S2CID 218831573 . ^ A Sánchez-Ferrer; J N Rodríguez-López; F García-Cánovas; F García-Carmona (1995). "Tyrosinase: A Comprehensive Review of Its Mechanism". Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology . 1247 (1): 1–11. doi :10.1016/0167-4838(94)00204-t . PMID 7873577 . ^ C Eicken; B Krebs; J C Sacchettini (1999). "Catechol Oxidase - Structure and Activity" . Current Opinion in Structural Biology 9 (6): 677–683. doi :10.1016/s0959-440x(99)00029-9 . PMID 10607672 . ^ Mayer AM (November 2006). "Polyphenol oxidases in plants and fungi: going places? A review". Phytochemistry . 67 (21): 2318–31. Bibcode :2006PChem..67.2318M . doi :10.1016/j.phytochem.2006.08.006 . PMID 16973188 . ^ Mauracher SG, Molitor C, Michael C, Kragl M, Rizzi A, Rompel A (March 2014). "High level protein-purification allows the unambiguous polypeptide determination of latent isoform PPO4 of mushroom tyrosinase" . Phytochemistry . 99 : 14–25. Bibcode :2014PChem..99...14M . doi :10.1016/j.phytochem.2013.12.016 . PMC 3969299 PMID 24461779 . ^ Mauracher SG, Molitor C, Al-Oweini R, Kortz U, Rompel A (September 2014). "Latent and active abPPO4 mushroom tyrosinase cocrystallized with hexatungstotellurate(VI) in a single crystal" . Acta Crystallographica. Section D, Biological Crystallography . 70 (Pt 9): 2301–15. doi :10.1107/S1399004714013777 . PMC 4157443 PMID 25195745 . ^ Kampatsikas I, Bijelic A, Pretzler M, Rompel A (August 2017). "Three recombinantly expressed apple tyrosinases suggest the amino acids responsible for mono- versus diphenolase activity in plant polyphenol oxidases" . Scientific Reports . 7 (1): 8860. Bibcode :2017NatSR...7.8860K . doi :10.1038/s41598-017-08097-5 . PMC 5562730 PMID 28821733 . ^ Kampatsikas I, Bijelic A, Pretzler M, Rompel A (May 2019). "A Peptide-Induced Self-Cleavage Reaction Initiates the Activation of Tyrosinase" . Angewandte Chemie . 58 (22): 7475–7479. doi :10.1002/anie.201901332 . PMC 6563526 PMID 30825403 . ^ Toledo L, Aguirre C (December 2017). "Enzymatic browning in avocado (Persea americana) revisited: History, advances, and future perspectives". Critical Reviews in Food Science and Nutrition . 57 (18): 3860–3872. doi :10.1080/10408398.2016.1175416 . PMID 27172067 . S2CID 205692816 .