Cysteinyl-tRNA Synthetase from Phaseolus aureus: Purification and Properties 1


l-Cysteinyl-tRNA synthetase (EC from Phaseolus aureus was purified approximately 300-fold and was free of contaminating aminoacyl-tRNA synthetases. Optimum assay conditions were determined and substrate specificity and inhibitor properties were investigated using the ATP-PPi exchange reaction. The Km values for l-cysteine, ATP, and PPi were 6.20 × 10−5m, 1.15 × 10−3m, and 1 × 10−3m, respectively. Both l-selenocysteine (Km = 5 × 10−5m) and α-l-aminobutyric acid (Km = 1 × 10−2m) acted as alternative substrates of the purified cysteinyl-tRNA synthetase. The enzyme was sensitive to sulfhydryl group reagents; it was inhibited by sulfide, 0-acetylserine, and reduced glutathione.

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