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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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).
12] Palou E, Lopez-Malo A, Barbosa-Canovas GV, Welti-Chanes J and BG Swanson Polyphenoloxidase activity and colour of blanched and hydrostatic pressure treated banana puree.
The homogenate was centrifuged at 10,000 g for 20 minutes and the supernatant was used as enzyme source for the assay of proteases, peroxidase, succinate dehydrogenase and polyphenoloxidase activities which were measured by the standard methodologies.
Cooper enzymes in isolated chloroplast: Polyphenoloxidase in Beta vulgaris.
Hydroxilated amino acids may be made into quinones in the presence of suitable enzymes such as a polyphenoloxidase (Thastrup 1985).
Although the activity of polyphenoloxidase was slightly enhanced, there was no perceptible change in the rate of browning.
Traditionally, the picked leaf is allowed to wither, or lose moisture, for a short time and then manipulated or rolled to partially rupture the leaf tissue, thus releasing plant juices containing active polyphenoloxidase enzymes.
Upon exposure to air, this chemical quickly begins darkening and turning sticky, owing to the presence of the enzyme polyphenoloxidase.