|PDB structures||RCSB PDB PDBe PDBsum|
|Gene Ontology||AmiGO / QuickGO|
Polyphenol oxidase (PPO or monophenol monooxygenase or Polyphenol oxidase I, chloroplastic) is a tetramer that contains four atoms of copper per molecule, and binding sites for two aromatic compounds and oxygen. The enzyme catalyses 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). It can also further catalyse the oxidation of o-diphenols to produce o-quinones.
PPO causes 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.
Structure and function
PPO is listed as a morpheein, a protein that can form two or more different homo-oligomers (morpheein forms), but must come apart and change shape to convert between forms. It exists as a monomer, trimer, tetramer, octamer or dodecamer, creating multiple functions.
Distribution and applications
A mixture of monophenol oxidase and catechol oxidase enzymes is present in nearly all plant tissues, and can also be found in bacteria, animals, and fungi. In insects, cuticular polyphenol oxidases are present and their products are responsible for desiccation tolerance.
Grape reaction product (2-S glutathionyl caftaric acid) is an oxidation compound produced by action of PPO on caftaric acid and found in wine. This compound production is responsible for the lower level of browning in certain white wines.
There are two types of inhibitor of PPO, those competitive to oxygen in the copper site of the enzyme and those competitive to phenolics. Tentoxin has also been used in recent research to eliminate the PPO activity from seedlings of higher plants. Tropolone is a grape polyphenol oxidase inhibitor. Another inhibitor of this enzyme is potassium pyrosulphite (K2S2O5). Banana root PPO is strongly inhibited by dithiothreitol and sodium metabisulfite.
Potassium dithionite (or potassium hydrosulfite) is also an inhibitor of PPO.
Hemocyanin is homologous to the phenol oxidases (e.g. tyrosinase) since both enzymes sharing type copper active site coordination. Hemocyanin also exhibits PPO activity, but with slowed kinetics from greater steric bulk at the active site. Partial denaturation actually improves hemocyanin’s PPO activity by providing greater access to the active site.
Aureusidin synthase is homologous to plant polyphenol oxidase, but contains certain significant modifications.
- "Polyphenol Oxidase". Worthington Enzyme Manual. Retrieved 13 September 2011.
- Mayer, AM (November 2006). "Polyphenol oxidases in plants and fungi: Going places? A review". Phytochemistry. 67 (21): 2318–2331. PMID 16973188. doi:10.1016/j.phytochem.2006.08.006.
- Jolley Jr, RL; Mason, HS (1965). "The Multiple Forms of Mushroom Tyrosinase. Interconversion". The Journal of Biological Chemistry. 240: PC1489–91. PMID 14284774.
- Jolley Jr, RL; Robb, DA; Mason, HS (1969). "The multiple forms of mushroom tyrosinase. Association-dissociation phenomena". The Journal of Biological Chemistry. 244 (6): 1593–9. PMID 4975157.
- Mallette, MF; Dawson, CR (1949). "On the nature of highly purified mushroom tyrosinase preparations". Archives of Biochemistry. 23 (1): 29–44. PMID 18135760.
- Function of polyphenol oxidase in higher plants. Kevin C. Vaughn and Stephen O. Duke, Physiologia Plantarum, January 1984, Volume 60, Issue 1, pages 106–112, doi:10.1111/j.1399-3054.1984.tb04258.x
- Sugumaran M, Lipke H (May 1983). "Quinone methide formation from 4-alkylcatechols: a novel reaction catalyzed by cuticular polyphenol oxidase". FEBS Letters. 155 (1): 65–68. doi:10.1016/0014-5793(83)80210-5.
- Quesnel V.C.; Jugmohunsingh K. (May 2006). "Browning reaction in drying caco". Journal of the Science of Food and Agriculture. 21 (10): 537–541. doi:10.1002/jsfa.2740211011.
- "Novel Food Information - Arctic Apple Events GD743 and GS784". Novel Foods Section, Food Directorate, Health Products and Food Branch, Health Canada, Ottawa. 20 March 2015. Retrieved 5 November 2016.
- Duke SO, Vaughn KC (April 1982). "Lack of involvement of polyphenol oxidase in ortho-hydroxylation of phenolic compounds in mung bean seedlings". Physiologia Plantarum. 54 (4): 381–385. doi:10.1111/j.1399-3054.1982.tb00696.x.
- Time-dependent inhibition of grape polyphenol oxidase by tropolone. Edelmira Valero, Manuela Garcia-Moreno, Ramon Varon and Francisco Garcia-Carmona, J. Agric. Food Chem., 1991, 39 (6), pp 1043–1046, doi:10.1021/jf00006a007
- Del Signore A, Romeoa F, Giaccio M (May 1997). "Content of phenolic substances in basidiomycetes". Mycological Research. 101 (5): 552–556. doi:10.1017/S0953756296003206.
- Wuyts, N; De Waele, D; Swennen, R (2006). "Extraction and partial characterization of polyphenol oxidase from banana (Musa acuminata Grande naine) roots". Plant Physiol Biochem. 44 (5-6): 308–314. PMID 16814556. doi:10.1016/j.plaphy.2006.06.005.
- Immunity and the Invertebrates Beck, Gregory and Habicht, Gail S, Scientific American, November 1996, pages 60-66
- Decker H, Tuczek F (August 2000). "Tyrosinase/catecholoxidase activity of hemocyanins: structural basis and molecular mechanism". Trends Biochem. Sci. 25 (8): 392–7. PMID 10916160. doi:10.1016/S0968-0004(00)01602-9.