title: Selenite reduction by the thioredoxin system: kinetics and identification of protein-bound selenide.
abstract: Selenite (SeO(3)(2-)) assimilation into a bacterial selenoprotein depends on thioredoxin (trx) reductase in Esherichia coli, but the molecular mechanism has not been elucidated. The mineral-oil overlay method made it possible to carry out anaerobic enzyme assay, which demonstrated an initial lag-phase followed by time-dependent steady NADPH consumption with a positive cooperativity toward selenite and trx. SDS-PAGE/autoradiography using (75)Se-labeled selenite as substrate revealed the formation of trx-bound selenium in the reaction mixture. The protein-bound selenium has metabolic significance in being stabilized in the divalent state, and it also produced the selenopersulfide (-S-SeH) form by the catalysis of E. coli trx reductase (TrxB).
authors.affiliation: Department of Bioresources Chemistry, Graduate School of Natural Science and Technology, Okayama University, Kita-ku, Okayama, Japan. tktamura@cc.okayama-u.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Tamura
authors.forename: Kumi
authors.initials: K
authors.lastname: Sato
authors.forename: Kentaro
authors.initials: K
authors.lastname: Komori
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imai
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Kuwahara
authors.forename: Takahiro
authors.initials: T
authors.lastname: Okugochi
authors.forename: Hisaaki
authors.initials: H
authors.lastname: Mihara
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Esaki
authors.forename: Kenji
authors.initials: K
authors.lastname: Inagaki
mesh_terms: D000693:Anaerobiosis; D001345:Autoradiography; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D007700:Kinetics; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism*; D012644:Selenium Radioisotopes / Q000378:metabolism*; D051140:Selenoproteins / Q000235:genetics / Q000378:metabolism*; D018038:Sodium Selenite / Q000378:metabolism; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D012644:Selenium Radioisotopes; D051140:Selenoproteins; D013879:Thioredoxins; D009249:NADP; D013880:Thioredoxin-Disulfide Reductase; D018038:Sodium Selenite