Journal Article

Bioconcentration Mechanism of Selenium by a Coccolithophorid, <i>Emiliania huxleyi</i>

Toshihiro Obata, Hiroya Araie and Yoshihiro Shiraiwa

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 10, pages 1434-1441
Published in print October 2004 | ISSN: 0032-0781
Published online October 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch164
Bioconcentration Mechanism of Selenium by a Coccolithophorid, Emiliania huxleyi

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We investigated the uptake and bioconcentration of the essential element selenium by a coccolithophorid, Emiliania huxleyi, using [75Se]selenite. The time course of 75Se uptake showed a biphasic pattern, namely a primary phase and a subsequent secondary phase. The primary and secondary phases are due to a rapid selenite uptake process that attained a stationary level within 2 min and a slow Se-accumulation process that continued at a constant rate for 4 h or longer, respectively. Kinetic analysis revealed that the selenite uptake process consists of two components, one saturable and one linearly related to substrate concentration. The Km of the saturable component was 29.8 nM selenite; the uptake activity of this component was suppressed by inhibitors of ATP biogenesis, suggesting that selenite uptake is driven by a high-affinity, active transport system. During a 6-h incubation of cells with [75Se]selenite, 70% of the intracellular 75Se was incorporated into low-molecular-mass compounds (LMCs), and 17% was incorporated into proteins, but [75Se]selenite was barely detectable. A pulse–chase experiment demonstrated that the 75Se that had accumulated in LMCs was transferred into proteins. When the syntheses of amino acids and proteins were each separately inhibited, 75Se incorporation into LMCs and proteins was decreased. These results suggest that E. huxleyi rapidly absorbs selenite, filling a small intracellular pool. Then, Se-containing LMCs are immediately synthesized from the selenite, creating a pool of LMCs that are then metabolized to selenoproteins.

Keywords: Keywords: Coccolithophorid — Emiliania huxleyi — Selenite uptake — Selenium accumulation.; Abbreviations: AOA, aminooxyacetic acid; CCCP, carbonyl cyanide 3-chlorophenylhydrazone; CHI, cycloheximide; DES, diethylstilbestrol; DIDS, 4,4′-diisothiocyanatostilbene-2,2′-disulfonate; DMSeP, dimethyl selenoniopropionate; ESM, Erd-Schreiber’s medium; l-MSO, l-Methionine sulfoximine; MA, Marine Art; LMC, low-molecular-mass compound; PS & NA, polysaccharides and nucleic acids; Se-Met, selenomethionine; SHAM, salicylhydroxamic acid; TCA, trichloroacetic acid.

Journal Article.  4308 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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