Selenite reduction by the thioredoxin system: kinetics and identification of protein-bound selenide |
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Authors: | Tamura Takashi Sato Kumi Komori Kentaro Imai Takeshi Kuwahara Mitsuhiko Okugochi Takahiro Mihara Hisaaki Esaki Nobuyoshi Inagaki Kenji |
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Affiliation: | Department of Bioresources Chemistry, Graduate School of Natural Science and Technology, Okayama University, Kita-ku, Okayama, Japan. tktamura@cc.okayama-u.ac.jp |
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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). |
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