Monodehydroascorbate Reductase in Spinach Chloroplasts and Its Participation in Regeneration of Ascorbate for Scavenging Hydrogen Peroxide

The primary reaction product of chloroplast ascorbate peroxidase activity was shown to be monodehydroascorbate radical (MDA). MDA reductase (EC 1.6.5.4) was localized in spinach chloroplast stroma. The MDA reductase activity of spinach chloroplasts, using NAD(P)H as electron donor, could account for the regeneration of ascorbate from MDA produced by ascorbate peroxidase activity. In the absence of MDA reductase, MDA disproportionated to ascorbate (AsA) and dehydroascorbate (DHA). The DHA was reduced to AsA by DHA reductase (EC 1.8.5.1) in chloroplasts. Both NADH and NADPH served as the electron donor of partially purified MDA reductase from spinach leaves.