https://biocyclopedia.com/index/plant_protocols/enzymes/polyphenol_oxidase.php
Phenol oxidases are copper proteins of wide occurrence in nature which catalyze the aerobic oxidation of certain phenolic substrates to quinones which are autoxidized to dark brown pigments generally known as melanins. These enzymes are assumed to be single enzymes with broad specificity although there is some evidence for the presence of more than one phenol oxidase in certain tissues. Each individual enzyme tends to catalyze the oxidation of one particular phenol or phenolic compound more readily than others. The polyphenol oxidase (PPO)comprises of catechol oxidase and laccase. The activities of these enzymes are important with regard to (a) plant defense mechanism against pests and diseases and (b) appearance palatability and use of plant products. Fresh fruits, vegetables, mushroom etc. contain these enzymes considerably.
..
Dietary Polyphenols and Their Biological Significance
RE: Disease-X