title: Ascorbate regeneration in bovine ocular tissues by NADH-dependent semidehydroascorbate reductase.
abstract: Despite its fast autoxidation in vitro, ascorbate remains in its reduced form in vivo, indicating a special mechanism may be involved in its regeneration. The presence of an NADH-dependent reductase system, semidehydroascorbate reductase (SDR), for regeneration of ascorbate from its partially oxidized form, semidehydroascorbate (SDA), was demonstrated in bovine ocular tissues after extraction in Triton X-100. Highest SDR activity was detected in retinal extracts in the order of retina greater than pigment epithelium-choroid = ciliary body greater than iris. Minimal or no activity was observed in lens extracts or in aqueous fluid. Freezing and thawing, or boiling, destroyed the NADH-dependent SDR activity. NADH oxidation was significantly reduced (22% of total activity) when assays with retinal extracts were performed at 5 degrees C. Treatment with 4 mM, N-ethylmaleimide reduced the rate of NADH oxidation to 73 or 42% compared with control values with retinal or ciliary body extracts, respectively.
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D002417:Cattle; D003683:Dehydroascorbic Acid / Q000378:metabolism; D005123:Eye / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D012160:Retina / Q000201:enzymology
chemical_list: D009243:NAD; D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH); D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid