Abstract
The oxidase activity of cucumber juice is
proportional to the amount of copper in the juice
after all the "free" copper and other extraneous
materials have been removed by prolonged dialysis
against pure water. This activity is much greater
than the catalytic power of copper in the ionic
state or copper in loose non-specific combination
with protein.
Removal of the copper present in cucumber
juice after long dialysis against water by
further dialysis against cyanide or dilute
mineral acid inactivates the oxidase.
Oxidase preparations inactivated by dialysis
against cyanide are restored to activity by the
addition of small excesses of copper sulphate, the
restored enzyme showing greater catalytic activity
than the amount of copper effecting the restoration.
It is concluded that cucumber juice contains
a discrete ascorbic acid oxidase, a metal protein
in which the prosthetic group is copper and which
is not identical with polyphenol oxidase
preparations.
