Polyphenol oxidase explained

Catechol oxidase
Altnames:Polyphenol oxidase
Ec Number:1.10.3.2

See main article: Catechol oxidase.

See main article: Tyrosinase.

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 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]

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,[11] [12] creating multiple functions.[13]

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.[14]

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.[15]

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[16] 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.

Plants make use of polyphenol oxidase as one in a suite of chemical defences against parasites.[17]

Inhibitors

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.[18] Tropolone is a grape polyphenol oxidase inhibitor.[19] Another inhibitor of this enzyme is potassium metabisulfite.[20] Banana root PPO activity is strongly inhibited by dithiothreitol and sodium metabisulfite,[21] as is banana fruit PPO by similar compounds including sodium dithionite and cysteine, in addition to ascorbic acid (vitamin C).[22]

Assays

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.[23] 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.[24] Alternative spectrophotometric method that involves the coupling of o-quinones with nucleophilic reagents such as 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) was also used.[25] Other techniques, such as activity staining assays with the use of polyacrylamide gel electrophoresis,[26] tritium-based radioactive assays,[27] oxygen consumption assay,[28] and nuclear magnetic resonance (NMR)-based assay were also reported and used.[29]

Enzymatic browning

Polyphenol oxidase is an enzyme found throughout the plant and animal kingdoms,[30] including most fruits and vegetables.[31] 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.[30] [31] [32] Enzymatic browning due to PPO can also lead to loss of nutritional content in fruits and vegetables, further lowering their value.[10] [31]

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.[33] Exposure to oxygen when sliced or pureed also leads to enzymatic browning by PPO in fruits and vegetables.[31] Examples in which the browning reaction catalyzed by PPO may be desirable include avocados, prunes, sultana grapes, black tea, and green coffee beans.[10] [31]

In mango

In mangoes, PPO catalyzed enzymatic browning is mainly caused by sap burn which leads to skin browning. 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.[33] PPO is located in mango skin, sap and pulp, with highest activity levels in skin.[31]

In avocado

PPO in avocados causes rapid browning upon exposure to oxygen,[10] a multistep process involving oxidation reactions of both monophenols and polyphenols, resulting in o-quinone products subsequently converted irreversibly into brown polymeric pigments (melanins).[34]

In apple

Present in the chloroplasts and mitochondria of all parts of an apple,[31] PPO is the major enzyme responsible for enzymatic browning of apples.[35] 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.[36] 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.[36] Browning also occurs in apple juices and purees when poorly handled or processed.[37]

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.[38]

In apricot

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.[39] Ascorbic acid/protease combinations constitute a promising practical anti-browning method as treated apricot purees preserved their color.[40]

In potato

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. 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.[32] In potatoes, PPO genes are not only expressed in potato tubers, but also in leaves, petioles, flowers and roots.[32]

In walnut

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.[41] [42]

In black poplar

A monomeric catechol oxidase from Populus nigra converts caffeic acid to quinone and melanine at injured cells.[43] [44]

Related enzymes

Prophenoloxidase is a modified form of the complement response found in some invertebrates, including insects, crabs and worms.[45]

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.[46]

Aureusidin synthase is homologous to plant polyphenol oxidase, but contains certain significant modifications.

Aurone synthase[47] 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 L-tyrosine and tyramine and must therefore be classified as catechol oxidase.[48]

See also

Notes and References

  1. Web site: Polyphenol Oxidase. Worthington Enzyme Manual. 13 September 2011.
  2. McLarin, Mark-Anthony . Leung, Ivanhoe K. H. . Substrate Specificity of Polyphenol Oxidase. . . 55. 274–308. 2020 . 3 . 10.1080/10409238.2020.1768209 . 32441137 . 218831573 .
  3. A Sánchez-Ferrer . J N Rodríguez-López . F García-Cánovas . F García-Carmona . Tyrosinase: A Comprehensive Review of Its Mechanism. . Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 1247 . 1–11 . 1995 . 1 . 10.1016/0167-4838(94)00204-t . 7873577 .
  4. C Eicken . B Krebs . J C Sacchettini . Catechol Oxidase - Structure and Activity. . . 9 . 677–683 . 1999 . 6 . 10.1016/s0959-440x(99)00029-9 . 10607672 .
  5. Mayer AM . Polyphenol oxidases in plants and fungi: going places? A review . Phytochemistry . 67 . 21 . 2318–31 . November 2006 . 16973188 . 10.1016/j.phytochem.2006.08.006 . 2006PChem..67.2318M .
  6. Mauracher SG, Molitor C, Michael C, Kragl M, Rizzi A, Rompel A . High level protein-purification allows the unambiguous polypeptide determination of latent isoform PPO4 of mushroom tyrosinase . Phytochemistry . 99 . 14–25 . March 2014 . 24461779 . 3969299 . 10.1016/j.phytochem.2013.12.016 . 2014PChem..99...14M .
  7. Mauracher SG, Molitor C, Al-Oweini R, Kortz U, Rompel A . 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 . September 2014 . 25195745 . 4157443 . 10.1107/S1399004714013777 .
  8. Kampatsikas I, Bijelic A, Pretzler M, Rompel A . Three recombinantly expressed apple tyrosinases suggest the amino acids responsible for mono- versus diphenolase activity in plant polyphenol oxidases . Scientific Reports . 7 . 1 . 8860 . August 2017 . 28821733 . 5562730 . 10.1038/s41598-017-08097-5 . 2017NatSR...7.8860K .
  9. Kampatsikas I, Bijelic A, Pretzler M, Rompel A . A Peptide-Induced Self-Cleavage Reaction Initiates the Activation of Tyrosinase . Angewandte Chemie . 58 . 22 . 7475–7479 . May 2019 . 30825403 . 6563526 . 10.1002/anie.201901332 .
  10. Toledo L, Aguirre C . Enzymatic browning in avocado (Persea americana) revisited: History, advances, and future perspectives . Critical Reviews in Food Science and Nutrition . 57 . 18 . 3860–3872 . December 2017 . 27172067 . 10.1080/10408398.2016.1175416 . 205692816 .
  11. Jolley RL, Mason HS . The Multiple Forms of Mushroom Tyrosinase. Interconversion . The Journal of Biological Chemistry . 240 . PC1489–91 . March 1965 . 10.1016/S0021-9258(18)97603-9 . 14284774 . free .
  12. Jolley RL, Robb DA, Mason HS . The multiple forms of mushroom tyrosinase. Association-dissociation phenomena . The Journal of Biological Chemistry . 244 . 6 . 1593–9 . March 1969 . 10.1016/S0021-9258(18)91800-4 . 4975157 . free .
  13. Mallette MF, Dawson CR . On the nature of highly purified mushroom tyrosinase preparations . Archives of Biochemistry . 23 . 1 . 29–44 . August 1949 . 18135760 .
  14. Vaughn KC, Duke SO . 1984 . Function of polyphenol oxidase in higher plants . Physiologia Plantarum . 60 . 1. 106–112 . 10.1111/j.1399-3054.1984.tb04258.x .
  15. Kampatsikas I, Rompel A . Similar but Still Different: Which Amino Acid Residues Are Responsible for Varying Activities in Type-III Copper Enzymes? . ChemBioChem . 1161–1175 . October 2020 . 22 . 7 . 33108057 . 10.1002/cbic.202000647. 1439-4227 . 8049008 . free .
  16. Sugumaran M, Lipke H . Quinone methide formation from 4-alkylcatechols: a novel reaction catalyzed by cuticular polyphenol oxidase . FEBS Letters . May 1983 . 155 . 1 . 65–68 . 10.1016/0014-5793(83)80210-5 . 84630585 .
  17. Thaler JS, Karban R, Ullman DE, Boege K, Bostock RM . Cross-talk between jasmonate and salicylate plant defense pathways: effects on several plant parasites . Oecologia . 131 . 2 . 227–235 . April 2002 . 28547690 . 10.1007/s00442-002-0885-9 . 2002Oecol.131..227T . 25912204 .
  18. Duke SO, Vaughn KC . Lack of involvement of polyphenol oxidase in ortho-hydroxylation of phenolic compounds in mung bean seedlings . Physiologia Plantarum . April 1982 . 54 . 4 . 381–385 . 10.1111/j.1399-3054.1982.tb00696.x .
  19. Valero E, Garcia-Moreno M, Varon R, Garcia-Carmona F . 1991 . Time-dependent inhibition of grape polyphenol oxidase by tropolone . J. Agric. Food Chem. . 39 . 6. 1043–1046 . 10.1021/jf00006a007 .
  20. Del Signore A, Romeoa F, Giaccio M . Content of phenolic substances in basidiomycetes . Mycological Research . May 1997 . 101 . 5 . 552–556 . 10.1017/S0953756296003206.
  21. Wuyts N, De Waele D, Swennen R . Extraction and partial characterization of polyphenol oxidase from banana (Musa acuminata Grande naine) roots . Plant Physiology and Biochemistry . 44 . 5–6 . 308–14 . 2006 . 16814556 . 10.1016/j.plaphy.2006.06.005 .
  22. Banana polyphenoloxidase. Preparation and properties . Palmer JK . 38 . 5 . 508–513 . 1963 . Oxford University Press . Plant Physiology. 10.1104/pp.38.5.508 . 16655824 . 549964 .
  23. García-Molina F, Muñoz JL, Varón R, Rodríguez-López JN, García-Cánovas F, Tudela J . A review on spectrophotometric methods for measuring the monophenolase and diphenolase activities of tyrosinase . Journal of Agricultural and Food Chemistry . 55 . 24 . 9739–49 . November 2007 . 17958393 . 10.1021/jf0712301 .
  24. Haghbeen K, Wue Tan E . Direct spectrophotometric assay of monooxygenase and oxidase activities of mushroom tyrosinase in the presence of synthetic and natural substrates . Analytical Biochemistry . 312 . 1 . 23–32 . January 2003 . 12479831 . 10.1016/S0003-2697(02)00408-6 .
  25. Espín JC, Morales M, Varón R, Tudela J, García-Cánovas F . A continuous spectrophotometric method for determining the monophenolase and diphenolase activities of apple polyphenol oxidase . Analytical Biochemistry . 231 . 1 . 237–46 . October 1995 . 8678307 . 10.1006/abio.1995.1526 .
  26. Rescigno A, Sollai F, Rinaldi AC, Soddu G, Sanjust E . Polyphenol oxidase activity staining in polyacrylamide electrophoresis gels . Journal of Biochemical and Biophysical Methods . 34 . 2 . 155–9 . March 1997 . 9178091 . 10.1016/S0165-022X(96)01201-8 .
  27. Pomerantz SH . Tyrosine hydroxylation catalyzed by mammalian tyrosinase: an improved method of assay . Biochemical and Biophysical Research Communications . 16 . 2 . 188–94 . June 1964 . 5871805 . 10.1016/0006-291X(64)90359-6 .
  28. Naish-Byfield S, Riley PA . Oxidation of monohydric phenol substrates by tyrosinase. An oximetric study . The Biochemical Journal . 288 . Pt 1 . 63–7 . November 1992 . 1445282 . 1132080 . 10.1042/bj2880063 .
  29. Li Y, Zafar A, Kilmartin PA, Reynisson J, Leung IK . Development and Application of an NMR-Based Assay for Polyphenol Oxidases . ChemistrySelect . 2 . 32 . 10435–41 . November 2017 . 10.1002/slct.201702144 .
  30. Ünal MÜ . Properties of polyphenol oxidase from Anamur banana (Musa cavendishii) . Food Chemistry . 100 . 3 . 909–913 . 10.1016/j.foodchem.2005.10.048. 2007 .
  31. Vámos-Vigyázó L . Polyphenol oxidase and peroxidase in fruits and vegetables . Critical Reviews in Food Science and Nutrition . 15 . 1 . 49–127 . 6794984 . 10.1080/10408398109527312 . 1981 .
  32. Thygesen PW, Dry IB, Robinson SP . Polyphenol oxidase in potato. A multigene family that exhibits differential expression patterns . Plant Physiology . 109 . 2 . 525–31 . October 1995 . 7480344 . 157616 . 10.1104/pp.109.2.525 .
  33. Robinson SP, Loveys BR, Chacko EK . 1993 . Polyphenol Oxidase Enzymes in the Sap and Skin of Mango Fruit . Functional Plant Biology . 20 . 1 . 99–107 . 10.1071/pp9930099 . 1445-4416.
  34. Web site: Shelby T. Peres . Kelsey A. Oonk . Kasandra J. Riley . The Avocado Lab: An Inquiry-Driven Exploration of an Enzymatic Browning Reaction . Rollins College, CourseSource . 8 March 2020 . 29 October 2019.
  35. Rocha AM, Cano MP, Galeazzi MA, Morais AM . 1998-08-01 . Characterisation of 'Starking' apple polyphenoloxidase . Journal of the Science of Food and Agriculture . 77 . 4 . 527–534 . 10.1002/(sici)1097-0010(199808)77:4<527::aid-jsfa76>3.0.co;2-e . 1097-0010. 10261/114868 . free .
  36. Son SM, Moon KD, Lee CY . Inhibitory effects of various antibrowning agents on apple slices . Food Chemistry . April 2001 . 73 . 1 . 23–30 . 10.1016/s0308-8146(00)00274-0 .
  37. Nicolas JJ, Richard-Forget FC, Goupy PM, Amiot MJ, Aubert SY . Enzymatic browning reactions in apple and apple products . Critical Reviews in Food Science and Nutrition . 34 . 2 . 109–57 . 8011143 . 10.1080/10408399409527653 . 1994 .
  38. Web site: Novel Food Information - Arctic Apple Events GD743 and GS784 . 20 March 2015 . Novel Foods Section, Food Directorate, Health Products and Food Branch, Health Canada, Ottawa . 5 November 2016.
  39. Derardja AE, Pretzler M, Kampatsikas I, Barkat M, Rompel A . Purification and Characterization of Latent Polyphenol Oxidase from Apricot (Prunus armeniaca L.) . Journal of Agricultural and Food Chemistry . 65 . 37 . 8203–8212 . September 2017 . 28812349 . 5609118 . 10.1021/acs.jafc.7b03210 .
  40. Derardja AE, Pretzler M, Kampatsikas I, Barkat M, Rompel A . Inhibition of apricot polyphenol oxidase by combinations of plant proteases and ascorbic acid . Food Chemistry . 4 . 100053 . December 2019 . 31650127 . 6804514 . 10.1016/j.fochx.2019.100053 .
  41. Panis F, Kampatsikas I, Bijelic A, Rompel A . Conversion of walnut tyrosinase into a catechol oxidase by site directed mutagenesis . Scientific Reports . 10 . 1 . 1659 . February 2020 . 32015350 . 6997208 . 10.1038/s41598-020-57671-x . 2020NatSR..10.1659P .
  42. Panis F, Rompel A . Identification of the amino acid position controlling the different enzymatic activities in walnut tyrosinase isoenzymes (jrPPO1 and jrPPO2) . Scientific Reports . 10 . 1 . 10813 . July 2020 . 32616720 . 7331820 . 10.1038/s41598-020-67415-6 . 2020NatSR..1010813P .
  43. Trémolières. Michèle. Bieth. Joseph G.. 1984. Isolation and characterization of the polyphenoloxidase from senescent leaves of black poplar. Phytochemistry. 23. 3. 501–505. 10.1016/s0031-9422(00)80367-2. 1984PChem..23..501T . 0031-9422.
  44. Rompel. Annette. Fischer. Helmut. Meiwes. Dirk. Büldt-Karentzopoulos. K.. Dillinger. Renée. Tuczek. Felix. Witzel. Herbert. Krebs. B.. 1999. 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 of Biological Inorganic Chemistry. en. 4. 1. 56–63. 10.1007/s007750050289. 10499103. 29871864. 1432-1327.
  45. Beck G, Habicht GS . Immunity and the Invertebrates . Scientific American . November 1996 . 275 . 5 . 60–66 . 10.1038/scientificamerican1196-60 . 8875808 . 1996SciAm.275e..60B .
  46. Decker H, Tuczek F . Tyrosinase/catecholoxidase activity of hemocyanins: structural basis and molecular mechanism . Trends in Biochemical Sciences . 25 . 8 . 392–7 . August 2000 . 10916160 . 10.1016/S0968-0004(00)01602-9 .
  47. Molitor C, Mauracher SG, Rompel A . Aurone synthase is a catechol oxidase with hydroxylase activity and provides insights into the mechanism of plant polyphenol oxidases . Proceedings of the National Academy of Sciences of the United States of America . 113 . 13 . E1806-15 . March 2016 . 26976571 . 4822611 . 10.1073/pnas.1523575113 . 2016PNAS..113E1806M . free .
  48. Molitor C, Mauracher SG, Pargan S, Mayer RL, Halbwirth H, Rompel A . Latent and active aurone synthase from petals of C. grandiflora: a polyphenol oxidase with unique characteristics . Planta . 242 . 3 . 519–37 . September 2015 . 25697287 . 4540782 . 10.1007/s00425-015-2261-0 .

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Polyphenol oxidase".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy.