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Figure 2: Role of DHAR and MDAR in L-ascorbic acid recycling. Asc is synthesized from L-galactono-1,4-lactone by L-galactono-1,4-lactone dehydrogenase (GLDH). When Asc is oxidized to monodehydroascorbate (MDHA), it can be reduced to Asc by monodehydroascorbate reductase (MDAR) or it can disproportionate non-enzymatically to Asc and dehydroascorbate (DHA). DHA spontaneously hydrolyzes to 2,3-diketogulonic acid unless salvaged by dehydroascorbate reductase (DHAR) which uses glutathione (GSH) as the reductant. Oxidized glutathione (GSSG) is reduced by glutathione reductase (GR) using NADPH as the reductant.