title: Regulation of the plant-type 5'-adenylyl sulfate reductase by oxidative stress.
abstract: 5'-Adenylyl sulfate (APS) reductase (EC 1.8.4.9) catalyzes a key reaction in the plant sulfate assimilation pathway leading to the synthesis of cysteine and the antioxidant glutathione. In Arabidopsis thaliana APS reductase is encoded by a family of three genes. In vitro biochemical studies revealed that the enzyme product derived from one of them (APR1) is activated by oxidation, probably through the formation of a disulfide bond. The APR1 enzyme is 45-fold more active when expressed in a trxB strain of Escherichia coli than in a trxB(+) wild type. The enzyme is inactivated in vitro by treatment with disulfide reductants and is reactivated with thiol oxidants. Redox titrations show that the regulation site has a midpoint potential of -330 mV at pH 8.5 and involves a two-electron redox reaction. Exposure of a variety of plants to ozone induces a rapid increase in APS reductase activity that correlates with the oxidation of the glutathione pool and is followed by an increase in free cysteine and total glutathione. During the response to ozone, the level of immunodetectable APS reductase enzyme does not increase. Treatment of A. thaliana seedlings with oxidized glutathione or paraquat induces APS reductase activity even when transcription or translation is blocked with inhibitors. The results suggest that a posttranslational mechanism controls APS reductase. A model is proposed whereby redox regulation of APS reductase provides a rapidly responding, self-regulating mechanism to control the glutathione synthesis necessary to combat oxidative stress.
authors.affiliation: Biotechnology Center for Agriculture and the Environment and the Plant Science Department, Rutgers University, New Brunswick, New Jersey 08901-8520, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Bick
authors.forename: A T
authors.initials: AT
authors.lastname: Setterdahl
authors.forename: D B
authors.initials: DB
authors.lastname: Knaff
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: L H
authors.initials: LH
authors.lastname: Pitcher
authors.forename: B A
authors.initials: BA
authors.lastname: Zilinskas
authors.forename: T
authors.initials: T
authors.lastname: Leustek
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D001937:Brassica / Q000201:enzymology / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D004790:Enzyme Induction / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D019803:Glutathione Disulfide / Q000494:pharmacology; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000235:genetics; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D050862:Oxidoreductases Acting on Sulfur Group Donors; D010126:Ozone / Q000494:pharmacology; D010269:Paraquat / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013880:Thioredoxin-Disulfide Reductase / Q000096:biosynthesis / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D011994:Recombinant Proteins; D013438:Sulfhydryl Compounds; D010126:Ozone; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; D013880:Thioredoxin-Disulfide Reductase; C019618:adenylylsulfate reductase; D010269:Paraquat; D019803:Glutathione Disulfide