Ascorbic acid oxidase from cucumber

Abstract

The ascorbic acid oxidase activity of cucumber juice was proportional to the Cu remaining after prolonged dialysis against water. The activity of such a prep. was about 100 X that of the Cu present in the ionic state. Complete removal of the Cu by dialysis against M/100 NaCN or M/100 HC1 inactivated the cucumber juice. Juice inactivated by dialysis against NaCN (but not HC1) and removal of excess NaCN was restored to activity by addition of Cu salts: with addition of 3 X the amt. of Cu originally present, 45% of the activity was restored, with 10 times, 67%. This activity was far greater than that of equivalent amts. of ionic Cu. The preps. from cucumber did not catalyse the oxidation of tyrosin or catechol. Cucumber juice evidently contained a discrete ascorbic acid oxidase, distinct from polyphenol oxidase, and having Cu as the presthetic group.