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Articles

Cysteinyl-tRNA Synthetase from Phaseolus aureus

Purification and Properties ¹

Alex Shrift^b

^a Department of Physical Biochemistry, John Curtin School of Medical Research, Australian National University, Canberra City, Australia 2601, Department of Biological Sciences, State University of New York, Binghamton, New York 13901

L-Cysteinyl-tRNA synthetase (EC 6.1.1.16) 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 x 10^–5M, 1.15 x 10^–3M, and 1 x 10^–3M, respectively. Both L-selenocysteine (Km = 5 x 10^–5M) and -L-aminobutyric acid (Km = 1 x 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.