MetaCyc Pathway: o-diquinones biosynthesis
Inferred from experiment

Enzyme View:

Pathway diagram: o-diquinones biosynthesis

This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Synonyms: biosynthesis of o-diquinones, fruit browning

Superclasses: BiosynthesisAromatic Compounds Biosynthesis

Some taxa known to possess this pathway include : Solanum lycopersicum, Solanum tuberosum, Vitis vinifera

Expected Taxonomic Range: Embryophyta

One of the reasons for fruit browning is the catalytic oxidation of phenolic substrates by polyphenoloxidase (PPO). Polyphenol oxidases catalyze two distinct reactions: the hydroxylation of monophenols to o-diphenols ( EC, tyrosinase), and the dehydrogenation of o-dihydroxyphenols to o-quinones ( EC, catechol oxidase). The products of the latter reaction are strong electrophiles that autoxidize, forming melanin, and are also capable of covalently modifying and crosslinking a variety of cellular nucleophiles. The formation of quinone adducts, usually brown or black, is the primary effect of PPO on fruit browning [Hunt93].

Some PPO endogenous substrates that have been identified in the pericarp tissues include flavan-3-ols and their dimers in lychee and longan, proanthocyanidins, (+)-catechin, and phlorizin in apple, dopamine in banana, and (-)-epicatechin and proanthocyanidin A2 in rambutan [Sun10a].

This pathway shows the biosynthesis of a typical o-diquinone, 1,2-benzoquinone, by the action of catechol oxidases in potato tubers [Hunt93] and fruits of tomato plants [Newman93]. In tomato the PPOs belong to a gene family of seven members. They fall into three structural classes and all are located on chromosome 8. The PPOs encode copper-binding sites typical of bacterial and fungal PPOs [Newman93].

Understanding this pathway is crucial to finding ways of delaying or preventing browning, as pericarp browning of fruits has serious commercial implications for storage and transport

Created 15-Mar-2011 by Pujar A, Boyce Thompson Institute


Hunt93: Hunt MD, Eannetta NT, Yu H, Newman SM, Steffens JC (1993). "cDNA cloning and expression of potato polyphenol oxidase." Plant Mol Biol 21(1);59-68. PMID: 7678763

Newman93: Newman SM, Eannetta NT, Yu H, Prince JP, de Vicente MC, Tanksley SD, Steffens JC (1993). "Organisation of the tomato polyphenol oxidase gene family." Plant Mol Biol 21(6);1035-51. PMID: 8098228

Sun10a: Sun J, Su W, Peng H, Zhu J, Xu L, Bruna NM (2010). "Two endogenous substrates for polyphenoloxidase in pericarp tissues of postharvest rambutan fruit." J Food Sci 75(6);C473-7. PMID: 20722899

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Shahar92: Shahar T, Hennig N, Gutfinger T, Hareven D, Lifschitz E (1992). "The tomato 66.3-kD polyphenoloxidase gene: molecular identification and developmental expression." Plant Cell 4(2);135-47. PMID: 1633491

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 19.5 on Mon Nov 30, 2015, BIOCYC11A.