Cysteinyl-tRNA Synthetase from Astragalus Species

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Abstract
L-Cysteinyl-tRNA synthetases (EC 6.1.1.16) from four Astragalus species were partially purified. The substrate specificities of the cysteinyl-tRNA synthetase from three selenium accumulator species (A. crotalariae, A bisulcatus, and A. racemosus) were compared with those from two nonaccumulator species (A. lentigenosus and Phaseolus aureus). All species had similar Km values for cysteine, selenocysteine, and α-aminobutyric acid except A. bisulcatus which failed to use selenocysteine as a substrate and which had a Km for cysteine four times greater than the Km values for other species.