Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Forteen species (17 strains) of phototrophic bacteria as well as one strain of Thiobacillus denitrificans were tested for cysteine synthase and S-sulfocysteine synthase. All strains contain cysteine sythase active with O-acetylserine; only the Chromatiaceae, two species of the Rhodospirillaceae and T. denitrificans contain S-sulfocysteine synthase. In six species repression by different sulfur compounds in the medium was studied. In Chromatium vinosum, cysteine synthase was found to be constitutive, while in the Rhodospirillaceae tested the enzyme is repressed by sulfide. Thiosulfate had a derepressive effect in Rhodopseudomonas globiformis but strongly repressed cysteine synthase in R. sulfidophila and R. palustris. Cysteine had only moderate effects with the species tested.
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PMID:Cysteine and S-sulfocysteine biosynthesis in phototrophic bacteria. 96 65

O-Acetylserine (thiol) lyase, the last enzyme in the cysteine biosynthetic pathway, was purified to homogeneity from spinach leaf chloroplasts. The enzyme has a molecular mass of 68,000 and consists of two identical subunits of Mr 35,000. The absorption spectrum obtained at pH 7.5 exhibited a peak at 407 nm due to pyridoxal phosphate, and addition of O-acetylserine induced a considerable modification of the spectrum. The pyridoxal phosphate content was found to be 1.1 per subunit of 35,000, and the chromophore was displaced from the enzyme by O-acetylserine, leading to a progressive inactivation of the holoenzyme. Upon gel filtration chromatography on Superdex 200, part of the chloroplastic O-acetylserine (thiol) lyase eluted in association with serine acetyltransferase at a position corresponding to a molecular mass of 310,000 (such a complex called cysteine synthase has been characterized in bacteria). The activity of O-acetylserine (thiol) lyase was optimum between pH 7.5 and 8.5. The apparent Km for O-acetylserine was 1.3 mM and for sulfide was 0.25 mM. The calculated activation energy was 12.6 kcal/mol at 10 mM O-acetylserine. The overall amino-acid composition of spinach chloroplast O-acetylserine (thiol) lyase was different than that determined for the same enzyme (cytosolic?) obtained from a crude extract of spinach leaves. A polyclonal antibody prepared against the chloroplastic O-acetylserine (thiol) lyase exhibited a very low cross-reactivity with a preparation of mitochondrial matrix and cytosolic proteins suggesting that the chloroplastic isoform was distinct from the mitochondrial and cytosolic counterparts.
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PMID:Purification and characterization of O-acetylserine (thiol) lyase from spinach chloroplasts. 137 15

Cysteine synthase (CSase) [O-acetyl-L-serine acetate-lyase (adding hydrogen sulfide), EC 4.2.99.8] catalyzes the formation of L-cysteine, the key step in sulfur assimilation in plants, from O-acetyl-L-serine and hydrogen sulfide. We report here the isolation and characterization of cDNA clones encoding cysteine synthase from spinach (Spinacia oleracea L.). Internal peptide sequences were obtained from V8 protease-digested fragments of purified CSase. A lambda gt10 cDNA library was constructed from poly(A)+ RNA of young green leaves of spinach. Screening with two synthetic mixed nucleotides encoding the partial peptide sequences revealed 19 positively hybridized clones among 2 x 10(5) clones. Nucleotide sequence analysis of two independent cDNA clones revealed a continuous open reading frame encoding a polypeptide of 325 amino acids with a calculated molecular mass of 34,185 Da. Sequence comparison of the deduced amino acids revealed 53% identity with CSases of Escherichia coli and Salmonella typhimurium. Sequence homology was also observed with other metabolic enzymes for amino acids in bacteria and yeast and with rat hemoprotein H-450. A bacterial expression vector was constructed and could genetically complement an E. coli auxotroph that lacks CSases. The accumulation of functionally active spinach CSase in E. coli was also demonstrated by immunoblotting and assaying enzymatic activity. Southern hybridization analysis showed the presence of two to three copies of the cDNA sequence in the genome of spinach. RNA blot hybridization suggested constitutive expression in leaves and roots of spinach.
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PMID:Molecular cloning and bacterial expression of cDNA encoding a plant cysteine synthase. 151 33

Regulation of the two enzymes in reverse trans-sulfuration was investigated in Saccharomyces cerevisiae. In wild-type strains, cystathionine gamma-lyase, but not cystathionine beta-synthase, was depressed nearly 15-fold if cells were starved for both inorganic and organic sulfur compounds. In a met17 strain which is defective of O-acetylserine and O-acetylhomoserine sulfhydrylase, the same enzyme was derepressed if organic sulfur compounds were limited; the repressive effect was in the order of glutathione greater than methionine greater than cysteine. The repressive effect of methionine was not observed, however, in a cys2 cys4 strain which is deficient of serine O-acetyltransferase and cystathionine beta-synthase, indicating that methionine itself is not the effector. The weak repressive effect of cysteine was attributed to inefficient uptake of this amino acid. Our observations indicate that cystathionine gamma-lyase is the target of regulation in reverse trans-sulfuration and that cysteine is very likely to be the effector of this regulation.
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PMID:Regulation of cystathionine gamma-lyase in Saccharomyces cerevisiae. 178 5

beta-(Isoxazolin-5-on-2-yl)alanine (BIA), a biosynthetic precursor of the neurotoxic amino acid beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (ODAP), was confirmed to be derived from O-acetyl-L-serine (OAS) and isoxazolin-5-one by cysteine synthase in higher plants. Some properties of this enzyme in the biosynthesis of BIA are described.
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PMID:Biosynthesis of beta-(isoxazolin-5-on-2-yl)alanine, the precursor of the neurotoxic amino acid beta-N-oxalyl-L-alpha,beta-diaminopropionic acid. 181 34

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

In order to ascertain the role of L-serine sulfhydro-lyase (L-serine hydro-lyase (adding homocysteine) EC 4.2.1.22) which also catalyzes sulfhydrylation of O-acetyl-L-serine (Yamagata, S. (1981) J. Bacteriol. 147, 688-690), the enzyme was partially purified from a wild-type strain and three cysteine auxotrophs of Saccharomyces cerevisiae, and the molecular and enzymatic properties of these preparations were compared. The results showed no significant difference in properties investigated, indicating that cysteine synthesis is exclusively performed in this organism through sulfhydrylation of O-acetyl-L-serine, catalyzed not by serine sulfhydro-lyase but by O-acetylserine . O-acetylhomoserine sulfhydro-lyase (Yamagata, S., Takeshima, K. and Naiki, N. (1974) J. Biochem. 75, 1221-1229). Insensitivity of the former enzyme to L-methionine also supported this conclusion.
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PMID:Partial purification and comparison of some properties of L-serine sulfhydro-lyase of Saccharomyces cerevisiae. 703 82

Extracts of Desulfovibrio vulgaris were found to contain serine transacetylase and cysteine synthase activities. When extracts were incubated with bisulfite and o-acetylserine, or acetyl coenzyme A plus L-serine, under a hydrogen atmosphere, cysteine was formed. Pyruvate served as a reductant for bisulfite reduction to sulfide and concomitantly provided the acetyl moiety for acetyl coenzyme A formation. Consequently, when extracts were incubated with pyruvate, bisulfite, and L-serine, cysteine synthesis resulted.
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PMID:Cysteine synthesis by Desulfovibrio vulgaris extracts. 736 31

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

Cystathionine beta-synthase (CBS) deficiency is the major cause of homocystinuria in humans. The most frequent symptoms of homocystinuria include: dislocated optic lenses, vascular disorders, skeletal abnormalities and mental retardation. Patients with this deficiency have elevated levels of homocyst(e)ine, methionine and low cysteine in their body fluids. These abnormal levels often partially or fully normalize upon treatment with pharmacological doses of vitamin B6. To investigate the molecular and biochemical basis for these conditions, it was necessary to determine the nucleotide and polypeptide sequence of CBS. We report here the human CBS cDNA sequence of 2,554 nucleotides encoding the CBS subunit of 551 amino acids. An intron of 214 bp appears to be retained in the 3'-untranslated region of most of the fibroblast and liver mRNA. We also report a frequent Mspl polymorphism in the 3'-untranslated sequence and two synonymous mutations in the coding region: 699C/T (Y233Y) and 1080C/T (A360A). The amino acid sequence similarity of human and rat CBS is greater than 90%; the enzyme also exhibits 52% similarity to O-acetylserine(thiol)-lyase from bacteria and plants. Lastly, we demonstrate that expression of the human enzyme in CHO cells yields enzymatically active protein of the expected size with a half-life of approximately 14 hrs.
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PMID:Human cystathionine beta-synthase cDNA: sequence, alternative splicing and expression in cultured cells. 790 80


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