Evidence about the catecholoxidase activity of the enzyme ascorbate oxidase extracted from Cucurbita pepo medullosa

Abstract Pure ascorbate oxidase ( l -ascorbate:oxygen oxidoreductase, EC 1.10.3.3) isolated from Cucurbita pepo medullosa , which is known to be specific for ascorbic acid, shows a secondary catecholoxidase activity at approx. pH 6.7. This activity was tested against natural and synthetic compounds possessing a catechol-like structure. Among natural compounds (+)-catechin furnishes the same complex oxidation mixture obtained with other oxidases. Among synthetic compounds, 3,5-di- t -butylcatechol and 4- t -butylcatechol give the corresponding o -quinones. The significance of this secondary activity in the darkening process of fruits and vegetables which contain ascorbate oxidase is also discussed.