title: Ascorbyl free radical and dehydroascorbate formation in rat liver endoplasmic reticulum.
abstract: The mechanism of ascorbate oxidation was studied in rat liver microsomes. A continuous consumption of the added ascorbate was observed, which was accompanied with a prompt appearance of ascorbyl free radical and dehydroascorbate. Microsomes sustained steady-state level of ascorbyl free radical and dehydroascorbate till ascorbate was present in the medium. Ascorbyl free radical formation was diminished when microsomes had been pretreated with heat or trypsine. It was also decreased by addition of quercetin, econazole or metal chelators, including the copper specific neocuproine. Enzymatic (superoxide dismutase, catalase) and nonenzymatic (dimethyl sulfoxide, mannitol) antioxidants did not modify the microsomal production of ascorbyl free radical. Investigation of the subcellular distribution of ascorbate oxidation showed that the microsomal fraction of liver had the highest activity. The decrease of ascorbate oxidation after protease treatment and the negligible increase upon permeabilization of microsomal vesicles showed that a membrane protein is responsible for the activity, which is exposed to the outer surface of the endoplasmic reticulum. The results indicate the presence of a primary enzymatic ascorbate oxidation in rat liver endoplasmic reticulum which is able to generate dehydroascorbate, an important source of the oxidizing environment in the endoplasmic reticulum.
authors.affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary.
authors.forename: András
authors.initials: A
authors.lastname: Szarka
authors.forename: Krisztián
authors.initials: K
authors.lastname: Stadler
authors.forename: Veronika
authors.initials: V
authors.lastname: Jenei
authors.forename: Eva
authors.initials: E
authors.lastname: Margittai
authors.forename: Miklós
authors.initials: M
authors.lastname: Csala
authors.forename: Judit
authors.initials: J
authors.lastname: Jakus
authors.forename: József
authors.initials: J
authors.lastname: Mandl
authors.forename: Gábor
authors.initials: G
authors.lastname: Bánhegyi
mesh_terms: D000818:Animals; D001204:Ascorbate Oxidase / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism*; D003683:Dehydroascorbic Acid / Q000378:metabolism*; D004721:Endoplasmic Reticulum; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D005609:Free Radicals; D011506:Proteins; D013438:Sulfhydryl Compounds; D001204:Ascorbate Oxidase; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid