O-Acetylserine sulfhydrylase

This enzyme [EC 4.2.99.8], also known as cysteine synthase and O-acetylserine sulfhydrylase, catalyzes the pyr-idoxal-phosphate-dependent reaction of H2S with O -acetylserine to produce cysteine and acetate. Some alkyl thiols, cyanide, pyrazole, and some other heterocyclic compounds can also act as acceptors. 

Cystathionine (3-lyase (cystathionase) O-Acetylserine sulfhydrylase (cysteine synthase)... 

Beta replacement is catalyzed by such enzymes of amino acid biosynthesis as tryptophan synthase (Chapter 25),184 O-acetylserine sulfhydrylase (cysteine synthase),185 186a and cystathionine (3-synthase (Chapter 24).187 188c In both elimination and (3 replacement an unsaturated Schiff base, usually of aminoacrylate or aminocrotonate, is a probable intermediate (Eq. 14-29). Conversion to the final products is usually assumed to be via hydrolysis to free aminoacrylate, tautomerization to an imino acid, and hydrolysis of the latter, e.g., to pyruvate and ammonium ion (Eq. 14-29). However, the observed stereospecific addition of a... 

The biosynthesis of L-cysteine entails the sulfhydryl transfer to an activated form of serine. This pathway to L-cysteine has been most thoroughly studied in E. coli. In the first step an acetyl group is transferred from acetyl-CoA to serine to yield (9-acetylserine (fig. 21.8a). The reaction is catalyzed by serine transacetylase. The formation of cysteine itself is catalyzed by O-acetylserine sulfhydrylase. 

Beta replacement is catalyzed by such enzymes of amino acid bios5mthesis as tryptophan synthase (Chapter 25), O-acetylserine sulfhydrylase (cysteine synihase), and cystathionine 3-synthase (Chapter In both elimination and (I replace-... 

S. L. (2005) The active site of O-acetylserine sulfhydrylase is the anchor point for bienzyme complex formation with serine acetyl-transferase./. Bacteriol. 187, 3201-3205. 

Cook, P.F., Tai, C.H., Hwang, C.C., Woehl, E.U., Dunn, M.F., and Schnackerz, K.D. (1996) Substitution of pyridoxal 5 -phosphate in the O-acetylserine sulfhydrylase from Salmonella typhimurium by cofactor analogs provides a test of the mechanism proposed for formation of the alpha-aminoacrylate intermediate. J. Biol. Chem. 271, 25842-25849. 

Pyridoxal 5 -phosphate-dependent a, -elimination reactions of O-acetylserine sulfhydrylase 01ACR49. 

Chirico, G, Bettati, S, Mozzarelli, A, Chen, Y, Muller, JD, and Gratton, E, Molecular heterogeneity of o-acetylserine sulfhydrylase by two-photon excited fluorescence fluctuation spectroscopy. Biophysical Journal80 (2001) 1973-1985. 

Francois, J.A. et al. (2006) Structural basis for interaction of O-acetylserine sulfhydrylase and serine acetyltransferase in ibc Arabidopsis cysteine synthase complex. Plant Cell 18,3647 3655... 

Kumaran, S. and Jez, J.M. (2007) Thermodynamics of the interaction between O-acetylserine sulfhydrylase and the C-terminus of serine acetyltransferase. Biochemistry (Mosc). 46, 5586-5594... 

A production method for the manufacture of cysteine by fermentation has been developed by Wacker Chemie. Building on this technology, an engineered E. coli strain overexpressing the enzyme O-acetylserine sulfhydrylase, which accepts a broad range of substrates, was used to produce a number of unnatural amino acids. This included triazole-1-yl-alanine, (S)-hydroxyethyl cysteine and phenylselenocysteine, which were prepared by feeding fermentations with unnatural precursor molecules (Figure 11.44) [287].These novel unnatural amino acids may prove useful for the synthesis of combinatorial (peptide) libraries. 

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