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Acc Chem Res. 2001 Jan;34(1):49-59.

Pyridoxal 5'-phosphate-dependent alpha,beta-elimination reactions: mechanism of O-acetylserine sulfhydrylase.

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  • 1Department of Chemical Engineering, Chenshiu Institute of Technology, Kaohsiung, Taiwan, Republic of China.


O-Acetylserine sulfhydrylase catalyzes the replacement of the beta-acetoxy group of O-acetyl-L-serine with sulfide to generate L-cysteine. The reaction represents the final step in the biosynthesis of L-cysteine in enteric bacteria and plants. A quinonoid intermediate has not been detected using a variety of kinetic and spectroscopic probes for the wild-type or mutant enzymes, ruling out an E1 mechanism. The structure of the external Schiff base intermediate indicates an anti elimination. O-Acetylserine sulfhydrylase is the only known pyridoxal 5'-phosphate-dependent enzyme that catalyzes a beta-elimination reaction to have an anti E2 mechanism.

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