Synthesis of selenocysteine by cysteine synthases from selenium accumulator and non-accumulator plants |
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Authors: | BHock Ng John W Anderson |
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Institution: | Botany Department, La Trobe University, Bundoora, Victoria 3083, Australia |
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Abstract: | Cysteine synthases were partially purified from leaf tissue of 3 selenium-accumulator species (Neptunia amplexicaulis, Astragalus racemosus and A. bisulcatus) and 4 non-accumulators (peas, white clover, A. sinicus and A. hamosus). The properties of all 7 enzymes with respect to cysteine synthesis from S2? and O-acetylserine (OAS) were similar. All of the enzymes also catalysed the synthesis of selenocysteine when S2? was replaced with Se2?. There were no distinct differences between the properties of the enzymes from selenium-accumulator and non-accumulator plants with respect to selenocysteine synthesis. Se2? inhibited the synthesis of cysteine and S2? inhibited the synthesis of selenocysteine implying competition between S2? and Se2? for the enzyme. The affinities of the enzymes for Se2? were substantially greater than for S2?, and Vmax (selenocysteine) was ca 7–48% of Vmax (cysteine). Isolated pea chloroplasts catalysed the synthesis of selenocysteine from OAS and Se2? at a rate of ca 22–26 μmol/mg Chl/hr. Sonicating the chloroplasts slightly enhanced the rate. |
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Keywords: | peas Leguminosae selenocysteine synthesis selenide assimilation sulphide assimilation |
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