title: Pyridoxal 5'-phosphate-dependent alpha,beta-elimination reactions: mechanism of O-acetylserine sulfhydrylase.
abstract: 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.
authors.affiliation: Department of Chemical Engineering, Chenshiu Institute of Technology, Kaohsiung, Taiwan, Republic of China.
authors.forename: C H
authors.initials: CH
authors.lastname: Tai
authors.forename: P F
authors.initials: PF
authors.lastname: Cook
mesh_terms: D003547:Cysteine Synthase / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation; D011732:Pyridoxal Phosphate / Q000378:metabolism*
chemical_list: D011732:Pyridoxal Phosphate; D003547:Cysteine Synthase