Soperoxide dismutase activity in ripening cucumber and pepper fruit

Superoxide dismutase (SOD, EC 1.15.1.1) was identified from ripening cucumber (Cucumis sativus L.) and pepper(Capsicum annuum L.) fruits, Gel filtration revealed the presence of two major peaks of SOD with molecular masses of about 32 000 and 40 000. Peroxidase activity was observed mainly in material with a molecular mass above 70 000. SOD activity was inhibited by cyanide but not by chloroform‐ethanol, indicating a cupro‐zinc enzyme. SOD activity levels were high in immature‐green fruits of both species, declining in cucumbers to a minimum during the mature‐green stage and in peppers during the mature‐green and breaker stages. SOD levels increased again until peppers became orange and cucumbers turned yellow, and finally decreased with ripening. The possible connection between SOD activity and tolerance to sunscald is discussed.