Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.5.1.47 (cysteine synthase)
 625 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

S-Sulfocysteine synthase was isolated from Salmonella typhimurium LT-2 to homogeneous form with polyacrylamide gel electrophoresis. The molecular weight of this enzyme was determined to be ca. 55,000. The enzyme consisted of two identically sized subunits, and it contained one pyridoxal phosphate per subunit. The enzyme catalyzed the biosynthesis of cysteine or S-methylcysteine from sulfide or methanethiol and O-acetylserine, respectively, in addition to the formation of S-sulfocysteine from thiosulfate and O-acetylserine. The enzyme is identical to cysteine synthase B. The intracellular level of this enzyme was regulated by lesser extents of the same factors as those effective for cysteine synthase A.
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PMID:Enzymatic proof for the identity of the S-sulfocysteine synthase and cysteine synthase B of Salmonella typhimurium. 637 37

Ferredoxin-dependent sulfite reductase (EC 1.8.7.1) catalyses the reduction of sulfite to sulfide, using reduced ferredoxin as an electron donor. An assay system was developed for measuring this enzyme activity in crude extracts and broken chloroplast preparations from leaves. The assay consists of a coupled system in which the sulfide formed is used for cysteine synthesis by added O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8). Cysteine thus formed is determined with ninhydrin under conditions where O-acetylserine does not react and serves as a measure for ferredoxin-dependent sulfite reductase activity. Cysteine synthesized in the assay can be determined from 10 to 200 nmol. One assay per minute can be performed.
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PMID:Measurement of ferredoxin-dependent sulfite reductase activity in crude extracts from leaves using O-acetyl-L-serine sulfhydrylase in a coupled assay system to measure the sulfide formed. 661 52

O-Acetylserine sulfhydrylase in cell-free extracts of Rhodospirillum tenue was markedly repressed after growth in the presence of sulfide or thiosulfate, whereas S-sulfocysteine synthase activity remained almost unchanged. Purification on DE52 cellulose resulted in the separation of two proteins: Protein I with a molecular weight of 57000 had O-acetylserine sulfhydrylase activity only, while protein II with a molecular weight of 46000 had S-sulfocysteine synthase activity in addition. The activity of protein II with O-acetylserine plus sulfide was about 1.5 of that with O-acetylserine plus thiosulfate. Protein I from sulfate-grown cells possessed 74% of the total O-acetylserine sulfhydrylase, protein II 26%. Growth with sulfide repressed only the synthesis of protein I, which after separation showed only 19% of the measurable O-acetylserine sulfhydrylase, whereas protein II now possessed 81%. Regulatory and kinetic phenomena of the two activities were studied. In addition to the phototrophic bacteria studied earlier, also Rhodomicrobium vannielii, Rhodopseudomonas acidophila, Rhodocyclus purpureus and Thiocystis violacea were found to contain O-acetylserine sulfhydrylase activities; the latter two species contained S-sulfocysteine synthase activities in addition.
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PMID:O-Acetylserine sulfhydrylase and S-sulfocysteine synthase activities of Rhodospirillum tenue. 661 27

Cell-free extracts of Salmonella typhimurium synthesize a mutagenic azide metabolite from sodium azide and O-acetylserine. S. typhimurium mutant DW379 (O-acetylserine sulfhydrylase-deficient) extracts were neither able to carry out this reaction not produce the mutagenic azide metabolite in vivo. The in vitro reaction was inhibited by sulfide but not by L-cysteine. The catalytic activity responsible for the mutagenic metabolite synthesis was stable to brief heating up to 55 degrees C and had a pH optimum between 7-7.4. These results suggest that the enzyme O-acetylserine sulfhydrylase catalyzes the reaction of azide with O-acetylserine to form a mutagenic azide metabolite.
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PMID:In vitro synthesis of a mutagenic azide metabolite by cell-free bacterial extracts. 680 99

L-Cystine and L-cysteine specifically reverse the mutagenic action of azide in Salmonella typhimurium and Escherichia coli. To establish whether the L-cysteine biosynthetic pathway is involved in azide-induced mutagenesis, several derivatives of a mutagen tester-strain of S. typhimurium bearing mutations in different cys genes were isolated. No mutagenic effect of azide was observed in a strain carrying mutation in the cysE gene, unless the incubation medium was supplemented with exogenous O-acetylserine. Our of 16 cysK mutants 14 were mutagenized by azide very poorly or not at all. These results indicate that the activity of O-acetylserine sulfhydrylase A, and the availability of O-acetylserine, one of the two co-substrates of the enzyme, are essential for the mutagenic action of azide in S. typhimurium.
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PMID:Involvement of the L-cysteine biosynthetic pathway in azide-induced mutagenesis in Salmonella typhimurium. 699 14

Studies with crude preparations obtained from a cysteine auxotroph of Saccharomyces cerevisiae showed that O-acetylserine sulfhydrylase could be separated from O-acetylhomoserine sulfhydrylase by chromatography on a DEAE-cellulose column and centrifugation in a sucrose density gradient. On the basis of sedimentation distance, the molecular weights of these enzymes were calculated to be about 99,000 and 182,000, respectively. The former did not react with the amino acid substrate of the latter, and vice versa. The wild-type strain was also demonstrated to possess O-acetylserine sulfhydrylase (molecular weight: about 96,000), in addition to a large amount of O-acetylserine-O-acetylhomoserine sulfhydrylase (Yamagata et al. (1974) J. Biochem. 75, 1221).
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PMID:Occurrence of low molecular weight O-acetylserine sulfhydrylase in the yeast Saccharomyces cerevisiae. 700 60

O-Acetyl-L-serine sulfhydrylase catalyzes the final step in the biosynthesis of cysteine from H2S and O-acetyl-L-serine in the fungus Cephalosporsium acremonium, a cephalosporin C-producing organism. We separated this enzyme from the closely related but less specific O-acetyl-L-homoserine sulfhydrylase and showed that O-acetyl-L-homoserine sulfhydrylase also catalyzes the formation of cysteine from O-acetyl-L-serine and H2S. The expression of O-acetyl-L-serine sulfhydrylase was regulated by exogenous methionine. In addition, this enzyme was inhibited by S-adenosyl-L-methionine and 5-formylpteroyl monoglutamic acid. The inhibition of both S-adenosyl-L-methionine and 5-formylpteroyl monoglutamic acid was noncompetitive. Results obtained with gel filtraton experiments in various buffer systems indicate an association-dissociation behavior of O-acetyl-L-serine sulfhydrylase.
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PMID:Regulatory properties of O-acetyl-L-serine sulfhydrylase of Cephalosporium acremonium: evidence of an isoenzyme and its importance in cephalosporin C biosynthesis. 719 Dec 38

Serine acetyltransferase (SATase; EC 2.3.1.30), which catalyzes the reaction connecting serine and cysteine/methionine metabolism, plays a regulatory role in cysteine biosynthesis in plants. We have isolated a cDNA clone encoding SATase by direct genetic complementation of a Cys- mutation in Escherichia coli using an expression library of Citrullus vulgaris (watermelon) cDNA. The cDNA encodes a polypeptide of 294 amino acids (31,536 Da) exhibiting 51% homology with that of E. coli SATase. DNA-blot analysis indicated the presence of a single copy of the SATase gene (sat) in watermelon. RNA hybridization analysis suggested the relatively ubiquitous and preferential expression in the hypocotyls of etiolated seedlings. Immunoblot analysis indicated the accumulation of SATase predominantly in etiolated plants. L-Cysteine, an end product of the cysteine biosynthetic pathway, inhibited the SATase in an allosteric manner, indicating the regulatory function of SATase in this metabolic pathway, whereas beta-(pyrazole-1-yl)-L-alanine, a secondary metabolite formed partly through the cysteine biosynthetic pathway, showed no inhibitory effect. A multi-enzyme complex was formed from recombinant proteins of SATase and cysteine synthase (O-acetylserine(thiol)-lyase) from watermelon, suggesting efficient metabolic channeling from serine to cysteine, preventing the diffusion of intermediary O-acetyl-L-serine.
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PMID:Molecular cloning and characterization of a plant serine acetyltransferase playing a regulatory role in cysteine biosynthesis from watermelon. 760

When cells of Escherichia coli are grown on lactate (or other carbon sources), an addition of serine to the medium causes growth inhibition. This growth inhibition is caused by inhibition by serine of homoserine dehydrogenase I, which is involved in threonine-isoleucine biosynthesis [Hama, H., Sumita, Y., Kakutani, Y., Tsuda, M., & Tsuchiya, T. (1990) Biochem. Biophys. Res. Commun. 168, 1211-1216]. We have cloned and sequenced genes which enhance the serine-sensitivity. Two open reading frames were found and designated as sseA and sseB. Introduction of either sseA or sseB gene, or both, into E. coli cells enhanced the serine-sensitivity. The sseA gene elicited stronger enhancement than sseB. The deduced amino acid sequence of SseA showed considerable similarity with that of bovine liver rhodanese, which catalyzes sulfur transfer from thiosulfate. We observed a twofold increase in rhodanese activity in E. coli cells harboring a plasmid carrying the sseA gene. The position of sseA in the genetic map is around 52'. However, sseA is different from cysM, which codes for O-acetylserine sulfhydrylase-B, an enzyme catalyzing sulfur transfer from thiosulfate to O-acetylserine, the map position of which is also around 52'.
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PMID:Enhancement of serine-sensitivity by a gene encoding rhodanese-like protein in Escherichia coli. 798 94

Three isoenzyme forms (designated A, B, and C) of O-acetylserine sulfhydrylase were purified from Datura innoxia suspension cultures. Isoenzyme A is the most abundant form, comprising 45-60% of the total activity. Isoenzymes C and B comprise 35-40% and 10-20% of the activity, respectively. The specific activities of the purified isoenzymes are similar (870-893 mumol of cysteine/min/mg of protein). Molecular masses for isoenzymes A, B, and C, estimated by analytical size exclusion high performance liquid chromatography, are 63, 86, and 63 kDa, respectively. Isoenzymes A and B are homodimers; isoenzyme C is a heterodimer. Spectral analysis indicates that these isoenzymes possess a pyridoxal 5'-phosphate cofactor that binds the O-acetylserine substrate. Binding is reversible by addition of the sulfide substrate. The O-acetylserine sulfhydrylase isoenzymes are active over a broad temperature range, with maximum activity between 42 and 58 degrees C. They are active only between pH 7 and 8, with optimal activity at pH 7.6. Kinetic analysis indicates these enzymes are allosterically regulated and exhibit positive cooperativity with respect to both substrates. They are inhibited by sulfide concentrations above 200 microM. The kinetic analysis together with the physical and spectrophotometric characteristics indicate that the O-acetylserine sulfhydrylase enzymes have two active sites.
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PMID:Purification and characterization of O-acetylserine sulfhydrylase isoenzymes from Datura innoxia. 811 66


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