Biology:Polyphenol oxidase

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Short description: Enzyme involved in fruit browning
Catechol oxidase
Identifiers
EC number1.10.3.2
Alt. namesPolyphenol oxidase
Databases
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BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Main page: Biology:Catechol oxidase
Main page: Biology: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 sulfur-containing 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][30][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.[32][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.[citation needed] 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.[citation needed] 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

References

  1. ↑ "Polyphenol Oxidase". Worthington Enzyme Manual. http://www.worthington-biochem.com/TY/default.html. 
  2. ↑ 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. 
  3. ↑ 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. 
  4. ↑ 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. https://zenodo.org/record/896893. 
  5. ↑ "Polyphenol oxidases in plants and fungi: going places? A review". Phytochemistry 67 (21): 2318–31. November 2006. doi:10.1016/j.phytochem.2006.08.006. PMID 16973188. Bibcode: 2006PChem..67.2318M. 
  6. ↑ "High level protein-purification allows the unambiguous polypeptide determination of latent isoform PPO4 of mushroom tyrosinase". Phytochemistry 99: 14–25. March 2014. doi:10.1016/j.phytochem.2013.12.016. PMID 24461779. Bibcode: 2014PChem..99...14M. 
  7. ↑ "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. doi:10.1107/S1399004714013777. PMID 25195745. 
  8. ↑ "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. doi:10.1038/s41598-017-08097-5. PMID 28821733. Bibcode: 2017NatSR...7.8860K. 
  9. ↑ "A Peptide-Induced Self-Cleavage Reaction Initiates the Activation of Tyrosinase". Angewandte Chemie 58 (22): 7475–7479. May 2019. doi:10.1002/anie.201901332. PMID 30825403. 
  10. ↑ 10.0 10.1 10.2 10.3 "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. doi:10.1080/10408398.2016.1175416. PMID 27172067. 
  11. ↑ "The Multiple Forms of Mushroom Tyrosinase. Interconversion". The Journal of Biological Chemistry 240: PC1489–91. March 1965. doi:10.1016/S0021-9258(18)97603-9. PMID 14284774. 
  12. ↑ "The multiple forms of mushroom tyrosinase. Association-dissociation phenomena". The Journal of Biological Chemistry 244 (6): 1593–9. March 1969. doi:10.1016/S0021-9258(18)91800-4. PMID 4975157. 
  13. ↑ "On the nature of highly purified mushroom tyrosinase preparations". Archives of Biochemistry 23 (1): 29–44. August 1949. PMID 18135760. 
  14. ↑ "Function of polyphenol oxidase in higher plants". Physiologia Plantarum 60 (1): 106–112. 1984. doi:10.1111/j.1399-3054.1984.tb04258.x. 
  15. ↑ "Similar but Still Different: Which Amino Acid Residues Are Responsible for Varying Activities in Type-III Copper Enzymes?". ChemBioChem 22 (7): 1161–1175. October 2020. doi:10.1002/cbic.202000647. ISSN 1439-4227. PMID 33108057. 
  16. ↑ "Quinone methide formation from 4-alkylcatechols: a novel reaction catalyzed by cuticular polyphenol oxidase". FEBS Letters 155 (1): 65–68. May 1983. doi:10.1016/0014-5793(83)80210-5. 
  17. ↑ "Cross-talk between jasmonate and salicylate plant defense pathways: effects on several plant parasites". Oecologia 131 (2): 227–235. April 2002. doi:10.1007/s00442-002-0885-9. PMID 28547690. Bibcode: 2002Oecol.131..227T. 
  18. ↑ "Lack of involvement of polyphenol oxidase in ortho-hydroxylation of phenolic compounds in mung bean seedlings". Physiologia Plantarum 54 (4): 381–385. April 1982. doi:10.1111/j.1399-3054.1982.tb00696.x. 
  19. ↑ "Time-dependent inhibition of grape polyphenol oxidase by tropolone". J. Agric. Food Chem. 39 (6): 1043–1046. 1991. doi:10.1021/jf00006a007. 
  20. ↑ "Content of phenolic substances in basidiomycetes". Mycological Research 101 (5): 552–556. May 1997. doi:10.1017/S0953756296003206. 
  21. ↑ "Extraction and partial characterization of polyphenol oxidase from banana (Musa acuminata Grande naine) roots". Plant Physiology and Biochemistry 44 (5–6): 308–14. 2006. doi:10.1016/j.plaphy.2006.06.005. PMID 16814556. 
  22. ↑ "Banana polyphenoloxidase. Preparation and properties". Plant Physiology (Oxford University Press) 38 (5): 508–513. 1963. doi:10.1104/pp.38.5.508. PMID 16655824. 
  23. ↑ "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. doi:10.1021/jf0712301. PMID 17958393. 
  24. ↑ "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. doi:10.1016/S0003-2697(02)00408-6. PMID 12479831. 
  25. ↑ "A continuous spectrophotometric method for determining the monophenolase and diphenolase activities of apple polyphenol oxidase". Analytical Biochemistry 231 (1): 237–46. October 1995. doi:10.1006/abio.1995.1526. PMID 8678307. 
  26. ↑ "Polyphenol oxidase activity staining in polyacrylamide electrophoresis gels". Journal of Biochemical and Biophysical Methods 34 (2): 155–9. March 1997. doi:10.1016/S0165-022X(96)01201-8. PMID 9178091. 
  27. ↑ "Tyrosine hydroxylation catalyzed by mammalian tyrosinase: an improved method of assay". Biochemical and Biophysical Research Communications 16 (2): 188–94. June 1964. doi:10.1016/0006-291X(64)90359-6. PMID 5871805. 
  28. ↑ "Oxidation of monohydric phenol substrates by tyrosinase. An oximetric study". The Biochemical Journal 288 (Pt 1): 63–7. November 1992. doi:10.1042/bj2880063. PMID 1445282. 
  29. ↑ "Development and Application of an NMR-Based Assay for Polyphenol Oxidases". ChemistrySelect 2 (32): 10435–41. November 2017. doi:10.1002/slct.201702144. 
  30. ↑ 30.0 30.1 30.2 "Properties of polyphenol oxidase from Anamur banana (Musa cavendishii)". Food Chemistry 100 (3): 909–913. 2007. doi:10.1016/j.foodchem.2005.10.048. 
  31. ↑ 31.0 31.1 31.2 31.3 31.4 31.5 31.6 "Polyphenol oxidase and peroxidase in fruits and vegetables". Critical Reviews in Food Science and Nutrition 15 (1): 49–127. 1981. doi:10.1080/10408398109527312. PMID 6794984. 
  32. ↑ 32.0 32.1 32.2 32.3 "Polyphenol oxidase in potato. A multigene family that exhibits differential expression patterns". Plant Physiology 109 (2): 525–31. October 1995. doi:10.1104/pp.109.2.525. PMID 7480344. 
  33. ↑ 33.0 33.1 "Polyphenol Oxidase Enzymes in the Sap and Skin of Mango Fruit". Functional Plant Biology 20 (1): 99–107. 1993. doi:10.1071/pp9930099. ISSN 1445-4416. 
  34. ↑ "The Avocado Lab: An Inquiry-Driven Exploration of an Enzymatic Browning Reaction". Rollins College, CourseSource. 29 October 2019. https://www.coursesource.org/sites/default/files/downloads/Peres-Avocado%20Lab-Inquiry-Driven%20Exploration%20of%20an%20Enzymatic%20Browning%20Reaction.pdf. 
  35. ↑ "Characterisation of 'Starking' apple polyphenoloxidase". Journal of the Science of Food and Agriculture 77 (4): 527–534. 1998-08-01. doi:10.1002/(sici)1097-0010(199808)77:4<527::aid-jsfa76>3.0.co;2-e. ISSN 1097-0010. 
  36. ↑ 36.0 36.1 "Inhibitory effects of various antibrowning agents on apple slices". Food Chemistry 73 (1): 23–30. April 2001. doi:10.1016/s0308-8146(00)00274-0. 
  37. ↑ "Enzymatic browning reactions in apple and apple products". Critical Reviews in Food Science and Nutrition 34 (2): 109–57. 1994. doi:10.1080/10408399409527653. PMID 8011143. 
  38. ↑ "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. http://www.hc-sc.gc.ca/fn-an/gmf-agm/appro/arcappsci-eng.php. 
  39. ↑ "Purification and Characterization of Latent Polyphenol Oxidase from Apricot (Prunus armeniaca L.)". Journal of Agricultural and Food Chemistry 65 (37): 8203–8212. September 2017. doi:10.1021/acs.jafc.7b03210. PMID 28812349. 
  40. ↑ "Inhibition of apricot polyphenol oxidase by combinations of plant proteases and ascorbic acid". Food Chemistry 4: 100053. December 2019. doi:10.1016/j.fochx.2019.100053. PMID 31650127. 
  41. ↑ "Conversion of walnut tyrosinase into a catechol oxidase by site directed mutagenesis". Scientific Reports 10 (1): 1659. February 2020. doi:10.1038/s41598-020-57671-x. PMID 32015350. Bibcode: 2020NatSR..10.1659P. 
  42. ↑ "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. doi:10.1038/s41598-020-67415-6. PMID 32616720. Bibcode: 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. doi:10.1016/s0031-9422(00)80367-2. ISSN 0031-9422. Bibcode: 1984PChem..23..501T. 
  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" (in en). Journal of Biological Inorganic Chemistry 4 (1): 56–63. doi:10.1007/s007750050289. ISSN 1432-1327. PMID 10499103. 
  45. ↑ "Immunity and the Invertebrates". Scientific American 275 (5): 60–66. November 1996. doi:10.1038/scientificamerican1196-60. PMID 8875808. Bibcode: 1996SciAm.275e..60B. http://www.scs.carleton.ca/~soma/biosec/readings/sharkimmu-sciam-Nov1996.pdf. 
  46. ↑ "Tyrosinase/catecholoxidase activity of hemocyanins: structural basis and molecular mechanism". Trends in Biochemical Sciences 25 (8): 392–7. August 2000. doi:10.1016/S0968-0004(00)01602-9. PMID 10916160. 
  47. ↑ "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. doi:10.1073/pnas.1523575113. PMID 26976571. Bibcode: 2016PNAS..113E1806M. 
  48. ↑ "Latent and active aurone synthase from petals of C. grandiflora: a polyphenol oxidase with unique characteristics". Planta 242 (3): 519–37. September 2015. doi:10.1007/s00425-015-2261-0. PMID 25697287. 



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