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Journal of Bacteriology, April 2003, p. 2277-2284, Vol. 185, No. 7
0021-9193/03/$08.00+0 DOI: 10.1128/JB.185.7.2277-2284.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Special Division for Human Life Technology, National Institute of Advanced Industrial Science and Technology (AIST, Kansai), Ikeda, Osaka 563-8577, Japan
Received 27 August 2002/ Accepted 6 January 2003
An O-acetylserine sulfhydrylase (OASS) from the hyperthermophilic archaeon Aeropyrum pernix K1, which shares the pyridoxal 5'-phosphate binding motif with both OASS and cystathionine ß-synthase (CBS), was cloned and expressed by using Escherichia coli Rosetta(DE3). The purified protein was a dimer and contained pyridoxal 5'-phosphate. It was shown to be an enzyme with CBS activity as well as OASS activity in vitro. The enzyme retained 90% of its activity after a 6-h incubation at 100°C. In the O-acetyl-L-serine sulfhydrylation reaction, it had a pH optimum of 6.7, apparent Km values for O-acetyl-L-serine and sulfide of 28 and below 0.2 mM, respectively, and a rate constant of 202 s-1. In the L-cystathionine synthetic reaction, it showed a broad pH optimum in the range of 8.1 to 8.8, apparent Km values for L-serine and L-homocysteine of 8 and 0.51 mM, respectively, and a rate constant of 0.7 s-1. A. pernix OASS has a high activity in the L-cysteine desulfurization reaction, which produces sulfide and S-(2,3-hydroxy-4-thiobutyl)-L-cysteine from L-cysteine and dithiothreitol.
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