title: alpha-Lipoic acid dependent regeneration of ascorbic acid from dehydroascorbic acid in rat liver mitochondria.
abstract: Rat liver mitochondria were examined for their ability to reduce dehydroascorbic acid to ascorbic acid in an alpha-lipoic acid dependent or independent manner. The alpha-lipoic acid dependent reduction was stimulated by factors that increased the NADH dependent reduction of alpha-lipoic acid to dihydrolipoic acid in coupled reactions. Optimal conditions for dehydroascorbic acid reduction to ascorbic acid were achieved in the presence of pyruvate, alpha-lipoic acid, and ATP. Electron transport inhibitors, rotenone and antimycin A, further enhanced the dehydroascorbic acid reduction. The reactions were strongly inhibited by 1 mM iodoacetamide or sodium arsenite. Mitoplasts were qualitatively similar to intact mitochondria in dehydroascorbate reduction activity. Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase reduced dehydroascorbic acid to ascorbic acid in an alpha-lipoic acid, coenzyme A, and pyruvate or alpha-ketoglutarate dependent fashion. Dehydroascorbic acid was also catalytically reduced to ascorbic acid by purified lipoamide dehydrogenase in an alpha-lipoic acid (K0.5 = 1.4 +/- 0.8 mM) and lipoamide (K0.5 = 0.9 +/- 0.3 mM) dependent manner.
authors.affiliation: Department of Biochemistry, Michigan State University, East Lansing 48824, USA.
authors.forename: D P
authors.initials: DP
authors.lastname: Xu
authors.forename: W W
authors.initials: WW
authors.lastname: Wells
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001205:Ascorbic Acid / Q000378:metabolism*; D003683:Dehydroascorbic Acid / Q000378:metabolism*; D008058:Dihydrolipoamide Dehydrogenase / Q000378:metabolism; D066298:In Vitro Techniques; D007658:Ketone Oxidoreductases / Q000378:metabolism; D007700:Kinetics; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism*; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D012402:Rotenone / Q000494:pharmacology; D008063:Thioctic Acid / Q000494:pharmacology*; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D009097:Multienzyme Complexes; D014475:Uncoupling Agents; D012402:Rotenone; D000968:Antimycin A; D008063:Thioctic Acid; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D008058:Dihydrolipoamide Dehydrogenase; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid