Changes in the antioxidative systems in mitochondria during ripening of pepper fruits

The presence of enzymes of the ascorbate–glutathione cycle was studied in mitochondria purified from green and red pepper (Capsicum annuum L.) fruits. All four enzymes, ascorbate peroxidase (APX; EC 1.11.1.11), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) were present in the isolated mitochondria of both fruit ripening stages. The activity of the reductive ascorbate–glutathione cycle enzymes (MDHAR, GR and DHAR) was higher in mitochondria isolated from green than from red fruits, while APX and the antioxidative enzyme superoxide dismutase (SOD; EC 1.15.1.1) were higher in the red fruits. The levels of ascorbate and L-galactono-γ-lactone dehydrogenase (GLDH; EC 1.3.2.3) activity were found to be similar in the mitochondria of both fruits. The higher APX and Mn-SOD specific activities in mitochondria from red fruits might play a role in avoiding the accumulation of any activated oxygen species generated in these mitochondria, and suggests an active role for these enzymes during ripening.