polyphenol oxidase

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,{{cite journal | vauthors = Jolley RL, Mason HS | title = The Multiple Forms of Mushroom Tyrosinase. Interconversion | journal = The Journal of Biological Chemistry | volume = 240 | pages = PC1489–91 | date = March 1965 | doi = 10.1016/S0021-9258(18)97603-9 | pmid = 14284774 | doi-access = free }}{{cite journal | vauthors = Jolley RL, Robb DA, Mason HS | title = The multiple forms of mushroom tyrosinase. Association-dissociation phenomena | journal = The Journal of Biological Chemistry | volume = 244 | issue = 6 | pages = 1593–9 | date = March 1969 | doi = 10.1016/S0021-9258(18)91800-4 | pmid = 4975157 | doi-access = free }} creating multiple functions.{{cite journal | vauthors = Mallette MF, Dawson CR | title = On the nature of highly purified mushroom tyrosinase preparations | journal = Archives of Biochemistry | volume = 23 | issue = 1 | pages = 29–44 | date = August 1949 | pmid = 18135760 }}

In plants, PPO is a plastidic enzyme with unclear synthesis and function. In functional chloroplasts, it may be involved in oxygen chemistry like mediation of pseudocyclic photophosphorylation.{{cite journal | vauthors = Vaughn KC, Duke SO | year = 1984 | title = Function of polyphenol oxidase in higher plants | journal = Physiologia Plantarum | volume = 60 | issue = 1| pages = 106–112 | doi = 10.1111/j.1399-3054.1984.tb04258.x }}

Enzyme nomenclature differentiates between monophenol oxidase enzymes (tyrosinases) and o-diphenol:oxygen oxidoreductase enzymes (catechol oxidases). The substrate preference of tyrosinases and catechol oxidases is controlled by the amino acids around the two copper ions in the active site.{{cite journal | vauthors = Kampatsikas I, Rompel A | title = Similar but Still Different: Which Amino Acid Residues Are Responsible for Varying Activities in Type-III Copper Enzymes? | journal = ChemBioChem | pages = 1161–1175 | date = October 2020 | volume = 22 | issue = 7 | pmid = 33108057 | doi = 10.1002/cbic.202000647|issn=1439-4227 | pmc = 8049008 | doi-access = free }}

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{{cite journal |vauthors=Sugumaran M, Lipke H | title = Quinone methide formation from 4-alkylcatechols: a novel reaction catalyzed by cuticular polyphenol oxidase | journal = FEBS Letters |date=May 1983 | volume = 155 | issue = 1 | pages = 65–68 | doi = 10.1016/0014-5793(83)80210-5 | s2cid = 84630585 }} 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.{{cn|date=July 2024}}

Plants make use of polyphenol oxidase as one in a suite of chemical defences against parasites.{{cite journal | vauthors = Thaler JS, Karban R, Ullman DE, Boege K, Bostock RM |author-link3=Diane Ullman| title = Cross-talk between jasmonate and salicylate plant defense pathways: effects on several plant parasites | journal = Oecologia | volume = 131 | issue = 2 | pages = 227–235 | date = April 2002 | pmid = 28547690 | doi = 10.1007/s00442-002-0885-9 | bibcode = 2002Oecol.131..227T | s2cid = 25912204 }}

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.{{cite journal |vauthors=Duke SO, Vaughn KC | title = Lack of involvement of polyphenol oxidase in ortho-hydroxylation of phenolic compounds in mung bean seedlings | journal = Physiologia Plantarum |date=April 1982 | volume = 54 | issue = 4 | pages = 381–385 | doi = 10.1111/j.1399-3054.1982.tb00696.x }} Tropolone is a grape polyphenol oxidase inhibitor.{{cite journal | vauthors = Valero E, Garcia-Moreno M, Varon R, Garcia-Carmona F | year = 1991 | title = Time-dependent inhibition of grape polyphenol oxidase by tropolone | journal = J. Agric. Food Chem. | volume = 39 | issue = 6| pages = 1043–1046 | doi = 10.1021/jf00006a007 }} Another inhibitor of this enzyme is potassium metabisulfite.{{cite journal |vauthors=Del Signore A, Romeoa F, Giaccio M |title=Content of phenolic substances in basidiomycetes | journal = Mycological Research |date=May 1997 | volume = 101 | issue = 5 | pages = 552–556 | doi = 10.1017/S0953756296003206}} Banana root PPO activity is strongly inhibited by dithiothreitol and sodium metabisulfite,{{cite journal | vauthors = Wuyts N, De Waele D, Swennen R | title = Extraction and partial characterization of polyphenol oxidase from banana (Musa acuminata Grande naine) roots | journal = Plant Physiology and Biochemistry | volume = 44 | issue = 5–6 | pages = 308–14 | year = 2006 | pmid = 16814556 | doi = 10.1016/j.plaphy.2006.06.005 }} as is banana fruit PPO by similar {{nowrap|sulfur-containing}} compounds including sodium dithionite and cysteine, in addition to ascorbic acid (vitamin C).{{cite journal | title = Banana polyphenoloxidase. Preparation and properties | vauthors = Palmer JK | volume = 38 | number = 5 | pages = 508–513 | year = 1963 | publisher = Oxford University Press | journal = Plant Physiology| doi = 10.1104/pp.38.5.508 | pmid = 16655824 | pmc = 549964 }}

Several assays were developed to monitor the activity of polyphenol oxidases and to evaluate the inhibition potency of polyphenol oxidase inhibitors. In particular, ultraviolet/visible (UV/Vis) spectrophotometry-based assays are widely applied.{{cite journal | vauthors = García-Molina F, Muñoz JL, Varón R, Rodríguez-López JN, García-Cánovas F, Tudela J | title = A review on spectrophotometric methods for measuring the monophenolase and diphenolase activities of tyrosinase | journal = Journal of Agricultural and Food Chemistry | volume = 55 | issue = 24 | pages = 9739–49 | date = November 2007 | pmid = 17958393 | doi = 10.1021/jf0712301 }} The most common UV/Vis spectrophotometry assay involves the monitoring of the formation of o-quinones, which are the products of polyphenol oxidase-catalysed reactions, or the consumption of the substrate.{{cite journal | vauthors = Haghbeen K, Wue Tan E | title = Direct spectrophotometric assay of monooxygenase and oxidase activities of mushroom tyrosinase in the presence of synthetic and natural substrates | journal = Analytical Biochemistry | volume = 312 | issue = 1 | pages = 23–32 | date = January 2003 | pmid = 12479831 | doi = 10.1016/S0003-2697(02)00408-6 }} Alternative spectrophotometric method that involves the coupling of o-quinones with nucleophilic reagents such as 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) was also used.{{cite journal | vauthors = Espín JC, Morales M, Varón R, Tudela J, García-Cánovas F | title = A continuous spectrophotometric method for determining the monophenolase and diphenolase activities of apple polyphenol oxidase | journal = Analytical Biochemistry | volume = 231 | issue = 1 | pages = 237–46 | date = October 1995 | pmid = 8678307 | doi = 10.1006/abio.1995.1526 }} Other techniques, such as activity staining assays with the use of polyacrylamide gel electrophoresis,{{cite journal | vauthors = Rescigno A, Sollai F, Rinaldi AC, Soddu G, Sanjust E | title = Polyphenol oxidase activity staining in polyacrylamide electrophoresis gels | journal = Journal of Biochemical and Biophysical Methods | volume = 34 | issue = 2 | pages = 155–9 | date = March 1997 | pmid = 9178091 | doi = 10.1016/S0165-022X(96)01201-8 }} tritium-based radioactive assays,{{cite journal | vauthors = Pomerantz SH | title = Tyrosine hydroxylation catalyzed by mammalian tyrosinase: an improved method of assay | journal = Biochemical and Biophysical Research Communications | volume = 16 | issue = 2 | pages = 188–94 | date = June 1964 | pmid = 5871805 | doi = 10.1016/0006-291X(64)90359-6 }} oxygen consumption assay,{{cite journal | vauthors = Naish-Byfield S, Riley PA | title = Oxidation of monohydric phenol substrates by tyrosinase. An oximetric study | journal = The Biochemical Journal | volume = 288 | issue = Pt 1 | pages = 63–7 | date = November 1992 | pmid = 1445282 | pmc = 1132080 | doi = 10.1042/bj2880063 }} and nuclear magnetic resonance (NMR)-based assay were also reported and used.{{cite journal |vauthors=Li Y, Zafar A, Kilmartin PA, Reynisson J, Leung IK | title = Development and Application of an NMR-Based Assay for Polyphenol Oxidases | journal = ChemistrySelect | volume = 2 | issue = 32 | pages = 10435–41 |date=November 2017 | doi = 10.1002/slct.201702144 }}

Polyphenol oxidase is an enzyme found throughout the plant and animal kingdoms,{{Cite journal | vauthors = Ünal MÜ |title=Properties of polyphenol oxidase from Anamur banana (Musa cavendishii) |journal=Food Chemistry |volume=100 |issue=3 |pages=909–913 |doi=10.1016/j.foodchem.2005.10.048|year=2007 }} including most fruits and vegetables.{{cite journal | vauthors = Vámos-Vigyázó L | title = Polyphenol oxidase and peroxidase in fruits and vegetables | journal = Critical Reviews in Food Science and Nutrition | volume = 15 | issue = 1 | pages = 49–127 | pmid = 6794984 | doi = 10.1080/10408398109527312 | year = 1981 }} PPO has importance to the food industry because it catalyzes enzymatic browning when tissue is damaged from bruising, compression or indentations, making the produce less marketable and causing economic loss.{{cite journal | vauthors = Thygesen PW, Dry IB, Robinson SP | title = Polyphenol oxidase in potato. A multigene family that exhibits differential expression patterns | journal = Plant Physiology | volume = 109 | issue = 2 | pages = 525–31 | date = October 1995 | pmid = 7480344 | pmc = 157616 | doi = 10.1104/pp.109.2.525 }} Enzymatic browning due to PPO can also lead to loss of nutritional content in fruits and vegetables, further lowering their value.

Because the substrates of these PPO reactions are located in the vacuoles of plant cells damaged mainly by improper harvesting, PPO initiates the chain of browning reactions.{{Cite journal | vauthors = Robinson SP, Loveys BR, Chacko EK |date=1993 |title=Polyphenol Oxidase Enzymes in the Sap and Skin of Mango Fruit |journal=Functional Plant Biology |volume=20 |issue=1 |pages=99–107 |doi=10.1071/pp9930099 |issn=1445-4416}} Exposure to oxygen when sliced or pureed also leads to enzymatic browning by PPO in fruits and vegetables. Examples in which the browning reaction catalyzed by PPO may be desirable include avocados, prunes, sultana grapes, black tea, and green coffee beans.

In mangoes, PPO catalyzed enzymatic browning is mainly caused by sap burn which leads to skin browning.{{citation needed|date=April 2018}} Catechol oxidase-type PPO is located in the chloroplasts of mango skin cells and its phenolic substrates in the vacuoles. Sap burn is therefore the initiating event of PPO in mango skin, as it breaks down cell compartments. PPO is located in mango skin, sap and pulp, with highest activity levels in skin.

PPO in avocados causes rapid browning upon exposure to oxygen, a multistep process involving oxidation reactions of both monophenols and polyphenols, resulting in o-quinone products subsequently converted irreversibly into brown polymeric pigments (melanins).{{cite web |author1=Shelby T. Peres |author2=Kelsey A. Oonk |author3=Kasandra J. Riley |title=The Avocado Lab: An Inquiry-Driven Exploration of an Enzymatic Browning Reaction |url=https://www.coursesource.org/sites/default/files/downloads/Peres-Avocado%20Lab-Inquiry-Driven%20Exploration%20of%20an%20Enzymatic%20Browning%20Reaction.pdf |publisher=Rollins College, CourseSource |access-date=8 March 2020 |date=29 October 2019}}

Present in the chloroplasts and mitochondria of all parts of an apple, PPO is the major enzyme responsible for enzymatic browning of apples.{{Cite journal | vauthors = Rocha AM, Cano MP, Galeazzi MA, Morais AM |date=1998-08-01 |title=Characterisation of 'Starking' apple polyphenoloxidase |journal=Journal of the Science of Food and Agriculture |volume=77 |issue=4 |pages=527–534 |doi=10.1002/(sici)1097-0010(199808)77:4<527::aid-jsfa76>3.0.co;2-e |issn=1097-0010|hdl=10261/114868 |hdl-access=free }} Due to an increase in consumer demand for pre-prepared fruits and vegetables, a solution for enzymatic browning has been a targeted area of research and new product development.{{Cite journal | vauthors = Son SM, Moon KD, Lee CY |title=Inhibitory effects of various antibrowning agents on apple slices |journal=Food Chemistry | date = April 2001 |volume=73 |issue=1 |pages=23–30 |doi=10.1016/s0308-8146(00)00274-0 }} As an example, pre-sliced apples are an appealing consumer product, but slicing apples induces PPO activity, leading to browning of the cut surfaces and lowering their esthetic quality. Browning also occurs in apple juices and purees when poorly handled or processed.{{cite journal | vauthors = Nicolas JJ, Richard-Forget FC, Goupy PM, Amiot MJ, Aubert SY | title = Enzymatic browning reactions in apple and apple products | journal = Critical Reviews in Food Science and Nutrition | volume = 34 | issue = 2 | pages = 109–57 | pmid = 8011143 | doi = 10.1080/10408399409527653 | year = 1994 }}

Arctic apples, an example of genetically modified fruit engineered to reduce PPO activity, are a suite of trademarked apples that contain a non-browning trait derived by gene silencing to suppress the expression of PPO, thus inhibiting fruit browning.{{cite web |url=http://www.hc-sc.gc.ca/fn-an/gmf-agm/appro/arcappsci-eng.php |title=Novel Food Information - Arctic Apple Events GD743 and GS784 |date=20 March 2015 |publisher=Novel Foods Section, Food Directorate, Health Products and Food Branch, Health Canada, Ottawa |access-date=5 November 2016}}

Apricot as a climacteric fruit undergoes fast post-harvest maturation. The latent PPO form can spontaneously activate during the first weeks of storage, generating the active enzyme with a molecular weight of 38 kDa.{{cite journal | vauthors = Derardja AE, Pretzler M, Kampatsikas I, Barkat M, Rompel A | title = Purification and Characterization of Latent Polyphenol Oxidase from Apricot (Prunus armeniaca L.) | journal = Journal of Agricultural and Food Chemistry | volume = 65 | issue = 37 | pages = 8203–8212 | date = September 2017 | pmid = 28812349 | pmc = 5609118 | doi = 10.1021/acs.jafc.7b03210 }} Ascorbic acid/protease combinations constitute a promising practical anti-browning method as treated apricot purees preserved their color.{{cite journal | vauthors = Derardja AE, Pretzler M, Kampatsikas I, Barkat M, Rompel A | title = Inhibition of apricot polyphenol oxidase by combinations of plant proteases and ascorbic acid | journal = Food Chemistry | volume = 4 | page = 100053 | date = December 2019 | pmid = 31650127 | pmc = 6804514 | doi = 10.1016/j.fochx.2019.100053 }}

Found in high concentrations in potato tuber peel and 1–2 mm of the outer cortex tissue, PPO is used in the potato as a defense against insect predation, leading to enzymatic browning from tissue damage.{{citation needed|date=April 2018}} Damage in the skin tissue of potato tuber causes a disruption of cell compartmentation, resulting in browning. The brown or black pigments are produced from the reaction of PPO quinone products with amino acid groups in the tuber. In potatoes, PPO genes are not only expressed in potato tubers, but also in leaves, petioles, flowers and roots.

In walnut (Juglans regia), two different genes (jr PPO1 and jr PPO2) encoding polyphenol oxidases have been identified. The two isoenzymes prefer different substrates, as jr PPO1 shows a higher activity towards monophenols, whereas jr PPO2 is more active towards diphenols.{{cite journal | vauthors = Panis F, Kampatsikas I, Bijelic A, Rompel A | title = Conversion of walnut tyrosinase into a catechol oxidase by site directed mutagenesis | journal = Scientific Reports | volume = 10 | issue = 1 | page = 1659 | date = February 2020 | pmid = 32015350 | pmc = 6997208 | doi = 10.1038/s41598-020-57671-x | bibcode = 2020NatSR..10.1659P }}{{cite journal | vauthors = Panis F, Rompel A | title = Identification of the amino acid position controlling the different enzymatic activities in walnut tyrosinase isoenzymes (jrPPO1 and jrPPO2) | journal = Scientific Reports | volume = 10 | issue = 1 | page = 10813 | date = July 2020 | pmid = 32616720 | pmc = 7331820 | doi = 10.1038/s41598-020-67415-6 | bibcode = 2020NatSR..1010813P }}

A monomeric catechol oxidase from Populus nigra converts caffeic acid to quinone and melanine at injured cells.{{Cite journal|last1=Trémolières|first1=Michèle|last2=Bieth|first2=Joseph G.|date=1984|title=Isolation and characterization of the polyphenoloxidase from senescent leaves of black poplar|journal=Phytochemistry|volume=23|issue=3|pages=501–505|doi=10.1016/s0031-9422(00)80367-2|bibcode=1984PChem..23..501T |issn=0031-9422}}{{Cite journal|last1=Rompel|first1=Annette|last2=Fischer|first2=Helmut|last3=Meiwes|first3=Dirk|last4=Büldt-Karentzopoulos|first4=K.|last5=Dillinger|first5=Renée|last6=Tuczek|first6=Felix|last7=Witzel|first7=Herbert|last8=Krebs|first8=B.|date=1999|title=Purification and spectroscopic studies on catechol oxidases from Lycopus europaeus and Populus nigra: Evidence for a dinuclear copper center of type 3 and spectroscopic similarities to tyrosinase and hemocyanin|journal=Journal of Biological Inorganic Chemistry|language=en|volume=4|issue=1|pages=56–63|doi=10.1007/s007750050289|pmid=10499103|s2cid=29871864|issn=1432-1327}}

Prophenoloxidase is a modified form of the complement response found in some invertebrates, including insects, crabs and worms.{{cite journal | vauthors = Beck G, Habicht GS | url = http://www.scs.carleton.ca/~soma/biosec/readings/sharkimmu-sciam-Nov1996.pdf | title = Immunity and the Invertebrates | journal= Scientific American | date = November 1996 | volume = 275 | issue = 5 | pages = 60–66 | doi = 10.1038/scientificamerican1196-60 | pmid = 8875808 | bibcode = 1996SciAm.275e..60B }}

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.{{cite journal | vauthors = Decker H, Tuczek F | title = Tyrosinase/catecholoxidase activity of hemocyanins: structural basis and molecular mechanism | journal = Trends in Biochemical Sciences | volume = 25 | issue = 8 | pages = 392–7 | date = August 2000 | pmid = 10916160 | doi = 10.1016/S0968-0004(00)01602-9 }}

Aureusidin synthase is homologous to plant polyphenol oxidase, but contains certain significant modifications.{{cn|date=July 2024}}

Aurone synthase{{cite journal | vauthors = Molitor C, Mauracher SG, Rompel A | title = Aurone synthase is a catechol oxidase with hydroxylase activity and provides insights into the mechanism of plant polyphenol oxidases | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 113 | issue = 13 | pages = E1806-15 | date = March 2016 | pmid = 26976571 | pmc = 4822611 | doi = 10.1073/pnas.1523575113 | bibcode = 2016PNAS..113E1806M | doi-access = free }} catalyzes the formation of aurones. Aurone synthase purified from Coreopsis grandiflora shows weak tyrosinase activity against isoliquiritigenin, but the enzyme does not react with the classic tyrosinase substrates {{sm|l}}-tyrosine and tyramine and must therefore be classified as catechol oxidase.{{cite journal | vauthors = Molitor C, Mauracher SG, Pargan S, Mayer RL, Halbwirth H, Rompel A | title = Latent and active aurone synthase from petals of C. grandiflora: a polyphenol oxidase with unique characteristics | journal = Planta | volume = 242 | issue = 3 | pages = 519–37 | date = September 2015 | pmid = 25697287 | pmc = 4540782 | doi = 10.1007/s00425-015-2261-0 }}

Laccase, a multi-copper oxidase, is often considered a subclass of polyphenol oxidase.{{cite book | url = https://doi.org/10.1016/C2022-0-01789-X | title = Laccase and Polyphenol Oxidase: Biochemistry and Biotechnological Applications | veditors = Leung IK | date = 2025 | doi = 10.1016/C2022-0-01789-X | isbn = 978-0-443-13301-5 | publisher = Academic Press }} Laccase and polyphenol oxidase differ in the type of substrates that they catalyse. Catachol oxidase (a type of polyphenol oxidase) catalyses the oxidation of ortho-diphenols to ortho-quinones. Tyrosinase (another type of polyphenol oxidase), catalyses both the oxidation of monophenols to ortho-diphenols, and the subsequent oxidation of ortho-diphenols to ortho-quinones. Laccase, in contrast, catalyses the oxidation of para-diphenols to para-quinones.{{cite journal | vauthors = Su J, Fu J, Wang Q, Silva C, Cavaco-Paulo A | title = Laccase: a green catalyst for the biosynthesis of poly-phenols | journal= Critical Reviews in Biotechnology | date = July 2017 | volume = 38 | issue = 2 | pages = 294-307 | doi = 10.1080/07388551.2017.1354353 | pmid = | hdl = 1822/51157 | hdl-access = free }}

• Catechol oxidase
• Tyrosinase

{{Reflist|2}}

{{Dioxygenases}}

{{Enzymes}}

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{{DEFAULTSORT:Polyphenol Oxidase}}

Category:EC 1.14.18

Category:Copper enzymes