Polyphenoloxidase


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Polyphenoloxidase

 

an oxidizing enzyme that is widespread in nature. Polyphenoloxidase is a protein of variable molecular weight (for example, 34,500 in mushrooms and 144,000 in tea leaves) that contains 0.2–0.3 percent copper. It catalyzes the oxidation of o-diphenols, as well as phenols, triphenols, and polyphenols, to produce the corresponding quinones; molecular oxygen acts as the hydrogen acceptor in this process.

Polyphenoloxidase apparently takes part in the respiration of plant cells (the reversible oxidation of polyphenols forms the intermediate stage for hydrogen transfer from a substrate to O2 in plants). By oxidizing the amino acid tyrosine in animals and humans, it plays a role in the formation of pigments called melanins, which are present in the skin, hair, and iris. Polyphenoloxidase also oxidizes tannins in tea leaves and causes the color of rye bread.

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The exposition of stone fruits to pre-storage before cold storage promotes the stability of cellular tissues and reduces the activity of oxidative enzymes such as polyphenoloxidase (Neves, Campos, Prill, & Roberto, 2013).
Along with its neutral salts, L-ascorbic acid is one of the main antioxidants used in plant products to prevent browning and other oxidative reactions in two ways: (1) by acting directly on the enzyme, complexing the copper of the prosthetic group of the polyphenoloxidase, causing its inhibition; and (2) by reducing the quinones to their previous form of phenols, preventing the formation of dark pigments (SAPERS; MILLER, 1998).
The enzymatic browning reaction occurs due to presence of the polyphenoloxidase enzyme (PPO) that catalyzes the oxidation reaction of phenolic compounds (Eissa, Fadel, Ibrahim, Hassan, & Elrashid 2006; Oliveira, Soares, Paula, & Viana 2008).
The surface color, pH, activity of phenylalanine ammonia-lyase, peroxidase and polyphenoloxidase enzymes, chlorophyll and carotenoids contents were evaluated.
It has been suggested that inactivating the enzymes responsible for browning (polyphenoloxidase, lipoxygenase, and peroxidase), during blanching improves both colour and flavour of vegetables [29].
Arnon, "Copper enzymes isolated chloroplasts, polyphenoloxidase in Beta vulgaris," Plant Physiology, vol.
Gu Y, Wang P, Kong CH (2009) Urease, invertase, dehydrogenase and polyphenoloxidase activities in paddy soil influenced by allelopathic rice variety.
Mishra, "Catalase, peroxidase, and polyphenoloxidase activities during rice leaf senescence," Plant Physiology, vol.
Increasing concentrations of lead, significantly (P < 0.05) decreased peroxidase enzyme activity (Figure 9), whereas polyphenoloxidase enzyme activity under different lead treatments were increased, but this different were not significant (Figure 10).
da Mota, "Effect of pH and temperature on peroxidase and polyphenoloxidase activities of litchi pericarp," Scientia Agricola, vol.