(1)植物はなぜビタミンCを多く含むのか? : 光・酵素毒防御系への関与(生命システムにおけるビタミンC)

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In plants, vitamin C (L-ascorbic acid : AsA) can accumulate to millimolar concentrations in both photosynthetic and nonphotosynthetic tissues. Three main types of biological activity can be defined for AsA : its function as an enzyme cofactor, as a radical scavenger, and as a donor/acceptor in electron transport either at the plasma membrane or in the chloroplasts. Even under optimal conditions, many metabolic processes, including the chloroplastic, mitochondrial, and plasma membrane-liked electron transport systems of higher plants, produce active oxygen species (AOS). Furthermore, the imposition of various environmental stresses can cause excess concentrations of AOS, resulting in oxidative damage at the cellular level. Therefore, antioxidants and antioxidantive enzymes function to interrupt the cascades of uncontrolled oxidation in each organelle. It is clear that AsA is a major primary antioxidant, reacting directly with AOS and a powerful secondary antioxidant, reducing the oxidized form of α-tocopherol. Plants and algae have evolved the AsA-glutathione cycle, consisting of ascorbate peroxidase (APX) and the enzymes related to the regeneration of AsA. APX isoenzymes are distributed in stromal APX and thylakoid membrane-bound APX in chloroplasts, microbody membrane-bound APX, and cytosolic APX and play important roles in the metabolism of H_2O_2 in plants. In this paper, the focus will be on recent molecular and physiological findings concerning APX isoenzymes in higher plants and algae. We also introduce a new biosynthetic pathway of AsA which proceeds via GDP-_D-mannnose and DGP-_L-galactose.
日本ビタミン学会の論文
2003-07-25

(1)植物はなぜビタミンCを多く含むのか? : 光・酵素毒防御系への関与(生命システムにおけるビタミンC)

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