O-acetyl-L-serine + hydrogen sulfide <=> L-cysteine + acetate.

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	PMID	Title & Author	Abstract	Year
0	11010893	MET17 and hydrogen sulfide formation in Saccharomyces cerevisiae. A Spiropoulos , L F Bisson	Commercial isolates of Saccharomyces cerevisiae differ in the production of hydrogen sulfide (H(2)S) during fermentation, which has been attributed to variation in the ability to incorporate reduced sulfur into organic compounds. We transformed two commercial strains (UCD522 and UCD713) with a plasmid overexpressing the MET17 gene, which encodes the bifunctional O-acetylserine/O-acetylhomoserine sulfhydrylase (OAS/OAH SHLase), to test the hypothesis that the level of activity of this enzyme limits reduced sulfur incorporation, leading to H(2)S release. Overexpression of MET17 resulted in a 10- to 70-fold increase in OAS/OAH SHLase activity in UCD522 but had no impact on the level of H(2)S produced. In contrast, OAS/OAH SHLase activity was not as highly expressed in transformants of UCD713 (0.5- to 10-fold) but resulted in greatly reduced H(2)S formation. Overexpression of OAS/OAH SHLase activity was greater in UCD713 when grown under low-nitrogen conditions, but the impact on reduction of H(2)S was greater under high-nitrogen conditions. Thus, there was not a good correlation between the level of enzyme activity and H(2)S production. We measured cellular levels of cysteine to determine the impact of overexpression of OAS/OAH SHLase activity on sulfur incorporation. While Met17p activity was not correlated with increased cysteine production, conditions that led to elevated cytoplasmic levels of cysteine also reduced H(2)S formation. Our data do not support the simple hypothesis that variation in OAS/OAH SHLase activity is correlated with H(2)S production and release.	2000
1	27935278	The GLO1 Gene Is Required for Full Activity of O-Acetyl Homoserine Sulfhydrylase Encoded by MET17. Matias I Kinzurik , Kien Ly , Karine M David , Richard C Gardner , Bruno Fedrizzi	During glycolysis, yeast generates methylglyoxal (MG), a toxic metabolite that affects growth. Detoxification can occur when glyoxylase I (GLO1) and glyoxylase II (GLO2) convert MG to lactic acid. We have identified an additional, previously unrecognized role for GLO1 in sulfur assimilation in the yeast Saccharomyces cerevisiae. During a screening for putative carbon-sulfur lyases, the glo1 deletion strain showed significant production of H2S during fermentation. The glo1 strain also assimilated sulfate inefficiently but grew normally on cysteine. These phenotypes are consistent with reduced activity of the O-acetyl homoserine sulfhydrylase, Met17p. Overexpression of Glo1p gave a dominant negative phenotype that mimicked the glo1 and met17 deletion strain phenotypes. Western analysis revealed reduced expression of Met17p in the glo1 deletion, but there was no indication of an altered conformation of Met17p or any direct interaction between the two proteins. Unravelling a novel function in sulfur assimilation and H2S generation in yeast for a gene never connected with this pathway provides new opportunities for the study of this molecule in cell signaling, as well as the potential regulation of its accumulation in the wine and beer industry.	2017
2	12606119	Transcription, nucleosome positioning and protein binding modulate nucleotide excision repair of the Saccharomyces cerevisiae MET17 promoter. Neville G Powell , Jose Ferreiro, Nikoletta Karabetsou, Jane Mellor, Raymond Waters	We have assessed how transcription, chromatin structure and protein binding modulate nucleotide excision repair in the upstream regulatory region and early coding region of the endogenous Saccharomyces cerevisiae gene MET17. Removal of UV-induced cyclobutane pyrimidine dimers was measured from these regions, in which transcription and chromatin structure could be regulated independently of each other. Distinct repair trends were apparent depending on transcriptional state. When transcription was repressed nucleosome positioning and protein binding as determined by chromatin immunoprecipitation and quantitative real-time PCR, were significant factors. Nucleosome positioning and/or protein binding effects were most apparent on the strand that becomes transcribed, with repair occurring fastest in a nucleosome free region but being retarded where regulatory proteins bound within this region. When transcription was derepressed the rate of repair increased on both strands in a region beginning 200 bp upstream of the TATA box and extending downstream into the coding region. This effect overrode the influences of nucleosome positioning and protein binding.	2003
3	795806	O-Acetylserine and O-acetylhomoserine sulfhydrylase of yeast. Further purification and characterization as a pyridoxal enzyme. S Yamagata, K Takeshima	O-Acetylserine-O-acetylhomoserine sulfhydrylase [EC class 4.2.99], catalyzing the sulfhydrylation of both O-acetyl-L-serine (OAS) and O-acetyl-L-homoserine (OAH) (O-acetyl-L-serine(O-acetyl-L-homoserine) + H2S leads to L-cysteine (L-homocysteine) + acetate), was extracted and purified from bakers' yeast by an improved method. The purified enzyme was shown to be homogeneous on polyacrylamide gel electrophoresis both in the absence and presence of sodium dodecylsulfate and by ultracentrifugal analysis. The apo-enzyme was protected by pyridoxal phosphate (PALP) from inactivation by heat, urea, and trypsin [EC 3.4.21.4], suggesting that the binding of PALP to the apo-enzyme rendered the conformation of the protein more stable. The holo-enzyme showed absorption peaks at 420 and 330 nm due to bound PALP, in addition to a peak at 280 nm. Upon reduction with borohydride, the 420-nm peak disappeared and an increase in the 330-nm peak occurred concomitant with loss of the catalytic activity. Lysine appeared to be the pyridoxal binding site, based on identification of pyridoxyl-lysine in the hydrolyzate of the holo-enzyme. It was shown by both spectral and chemical determinations that 4 moles of PALP could bind to 200,000 g of apo-protein. The apo-enzyme showed a lower association constant with PALP than some other enzymes. Pyridoxal inhibited the activity competitively with respect to PALP. Based on these findings, it appears that the reaction mechanism of this enzyme is similar to those of other pyridoxal enzymes.	1976

Yamagata S , Takeshima K . O-Acetylserine and O-Acetylhomoserine Sulfhydrylase of Yeast Further Purification and Characterization as a Pyridoxal Enzyme[J]. Journal of Biochemistry, 1976, 80(4):777-785.