Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:4.2.1.22 (cystathionine beta-synthase)
965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
...
PMID:Molecular cloning and bacterial expression of cDNA encoding a plant cysteine synthase. 151 33

Cystathionine was cleaved into 2-ketobutyric acid, cysteine and ammonia by cystathionase. 2-Ketobutyric acid was converted into 3-ethyl-2-hydroxy-6,7-dimethoxyquinoxaline (EHDQ) by reaction with 1,2-diamino-4,5-dimethoxybenzene. When EHDQ was measured in a mobile phase of pH 2.1 using high-performance liquid chromatography with ultraviolet detection, 250 pmol of L-cystathionine in 250 microliters of the reaction mixture could be determined. Because EHDQ has a strong fluorescence in a mobile phase of pH 6.5 at 447 nm, on excitation at 365 nm, as little as 2.5 pmol of cystathionine in 250 microliters of the reaction mixture could be determined by high-performance liquid chromatography with fluorimetric detection. Cystathionase activity was assayed on the basis of the same principle by determining cystathionine in as little as 63 ng of rat liver by fluorimetric detection. Cystathionine beta-synthase activity was measured by the same method by determining cystathionine formed in only 113 ng of wet weight of rat liver. Using these methods, both cystathionine beta- and gamma-lyase activities in Saccharomyces cerevisiae were determined, because quinoxaline derivatives from pyruvate and 2-ketobutyrate could be measured simultaneously by high-performance liquid chromatography.
...
PMID:Sensitive determination of cystathionine and assays for cystathionine beta- and gamma-lyase, as well as cystathionine beta-synthase, using high-performance liquid chromatography. 162 86

Glutathione-deficient mutants (gshA) of the yeast Saccharomyces cerevisiae, impaired in the first step of glutathione (GSH) biosynthesis were studied with respect to the regulation of enzymes involved in GSH catabolism and cysteine biosynthesis. Striking differences were observed in the content of the sulphur amino acids when gshA mutants were compared to wild-type strains growing on the same minimal medium. Furthermore, all mutants examined showed a derepression of gamma-glutamyltranspeptidase (gamm-GT), the enzyme initiating GSH degradation. However, gamma-cystathionase and cysteine synthase were unaffected by the GSH deficiency as long as the nutrient sulphate source was not exhausted. The results suggest that the mutants are probably not impaired in the sulphate assimilation pathway, but that the gamma-glutamyl cycle could play a leading role in the regulation of the sulphur fluxes. Studies of enzyme regulation showed that the derepression of gamma-GT observed in the gshA strains was most probably due to an alteration of the thiol status. The effectors governing the biosynthesis of cysteine synthase and gamma-cystathionase seemed different from those playing a role in gamma-GT regulation and it was only under conditions of total sulphate deprivation that all these enzymes were derepressed. As a consequence the endogenous pool of GSH was used in the synthesis of cysteine. GSH might, therefore, fulfil the role of a storage compound.
...
PMID:Glutathione as an endogenous sulphur source in the yeast Saccharomyces cerevisiae. 167 26

Eight classes of pyridoxal 5'-phosphate dependent enzymes have been investigated in Nippostrongylus brasiliensis in parallel with rat tissues. The range of decarboxylases detected in N. brasiliensis was limited in comparison with rat tissues. N. brasiliensis possessed a highly active L-serine hydroxymethyltransferase, but in contrast with rat liver, 5-aminolevulinic acid synthetase was absent. Similar levels of L-serine and L-threonine dehydratase activities were detected in N. brasiliensis and rat liver, and both organisms lacked L-alanine racemase, L-tryptophan synthetase and L-methionine gamma-lyase. The demonstration of cystathionine beta-synthase and gamma-cystathionase in N. brasiliensis suggests the presence of a functional trans-sulphuration sequence. The substrate specificities of the nematode cystathionine beta-synthase and gamma-cystathionase varied significantly from those of the corresponding mammalian enzymes. Particularly striking was the ability of N. brasiliensis cystathionine beta-synthase to catalyse the non-mammalian 'activated L-serine sulphydrase' reaction (L-cysteine + R-SH----cysteine thioether + H2S). N. brasiliensis and rat liver exhibited comparable abilities to transaminate amino acids via the 2-oxoglutarate: glutamate system.
...
PMID:Pyridoxal 5'-phosphate dependent enzymes in the nematode Nippostrongylus brasiliensis. 175 92

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.
...
PMID:Regulation of cystathionine gamma-lyase in Saccharomyces cerevisiae. 178 5

The activities of gamma-cystathionase and cystathionine beta-synthase were investigated in a range of gastrointestinal, free-living and entomophagous nematodes. Although nematode gamma-cystathionase used the same range of substrates as the mammalian hepatic enzyme, its activity was extremely low and there were significant interspecies variations with respect to the relative order of active substrates. Like the mammalian liver enzyme, nematode cystathionine beta-synthase showed activity in the directions of both cystathionine synthesis and the forward and reverse "L-serine sulphhydrase" reactions. However, the most important feature of the survey was the widespread ability of nematode cystathionine beta-synthase to catalyse the non-mammalian "activated L-serine sulphhydrase" reaction (L-cysteine + R-SH----cysteine thioether + H2S). Additional survey work revealed that the ability to catalyse the activated L-serine sulphhydrase reaction was almost universal amongst nematodes. Activated L-serine sulphhydrase activity was also demonstrated in the acanthocephalan Pomphorhynchus laevis but was absent from cestodes and digeneans.
...
PMID:Cystathionine beta-synthase and gamma-cystathionase in helminths. 180 16

We examined the change in glutathione metabolism in vitamin B-6-deficient rats. Vitamin B-6-deficient rats were fed a vitamin B-6-deficient diet containing 0.56% methionine and 0.075% cystine for 8 wk. Controls were fed an identical diet supplemented with 10 mg pyridoxine hydrochloride/kg diet. Glutathione concentrations in each organ examined were similar in control and vitamin B-6-deficient rats, and the values were comparably lower after intraperitoneal injection of diethylmaleate. However, buthionine sulfoximine caused a significantly greater decrease in glutathione levels in the liver and lungs of vitamin B-6-deficient rats relative to controls. Glutathione peroxidase activity in the liver of vitamin B-6-deficient rats was higher than in control animals; however, glutathione transferase activity in tissues other than liver of vitamin B-6-deficient rats was higher than in the controls. The activities of gamma-glutamyl-transferase in the liver and spleen of vitamin B-6-deficient rats were significantly lower than control values. The holoenzyme activities of cystathionine beta-synthase and cystathionine gamma-lyase in the liver of vitamin B-6-deficient rats were markedly reduced. These findings indicate that although the activities of enzymes that synthesize cysteine from methionine were decreased by vitamin B-6 deficiency, the level of synthesis and supply of cysteine in vitamin B-6-deficient rats were sufficient to maintain the same glutathione level as in controls, and that glutathione utilization in the liver was accelerated by vitamin B-6 deficiency.
...
PMID:Glutathione levels and related enzyme activities in vitamin B-6-deficient rats fed a high methionine and low cystine diet. 188 Jun 14

A yeast strain highly resistant to propargylglycine (an inhibitor of cystathionine gamma-lyase) was isolated from air. It was partially characterized, but it has not been identified with any known yeast species. Its sulphur amino acid metabolism differed from that of other fungi by the lack of the reverse transsulphuration pathway from methionine to cysteine, as no activity of cystathionine beta-synthase or cystathionine gamma-lyase was found. The functional lack of this pathway was confirmed by growth tests and by experiments with [35S]methionine. In contrast to Saccharomyces cerevisiae neither homocysteine synthase nor the sulphate assimilation pathway were repressible by methionine in the new strain; on the contrary, a regulatory effect of cysteine was observed.
...
PMID:A yeast with unusual sulphur amino acid metabolism. 207 24

To assess the extent to which low hepatic gamma-cystathionase levels affect methionine flux to cysteine in hepatocytes, the effect of inhibition of gamma-cystathionase activity with propargylglycine on the metabolism of L-[35S]methionine was determined in studies with freshly isolated rat hepatocytes. gamma-Cystathionase activity was inhibited 25%, 42%, 63% and 76% (maximal inhibition) by treatment with 2.5 mumol/L, 0.01 mmol/L, 0.02 mmol/L and 2 mmol/l propargylglycine, respectively. Inhibition of gamma-cystathionase activity with up to 0.02 mmol/L propargylglycine had no statistically significant effect on [35S]glutathione, [35S]sulfate or [35S]cysteine formation from [35S]methionine. However, treatment of cells with 2 mmol/L propargylglycine markedly inhibited the metabolism of [35S]methionine to [35S]glutathione by 93%, to [35S]sulfate by 88% and to [35S]cysteine by 89%; [35S]cystathionine accumulation in these incubation systems was 60 times control. Hepatic gamma-cystathionase activity in premature infants has been reported to be about 23% of mature levels (Zlotkin and Anderson, 1982; Pediatr. Res. 16: 65-68); this level of gamma-cystathionase activity may limit cysteine synthesis by the methionine transsulfuration pathway. No evidence for cysteine synthesis from serine and sulfide, which can be catalyzed by cystathionine beta-synthase, or for methionine metabolism by an S-adenosylmethionine-independent pathway was obtained.
...
PMID:Role of the transsulfuration pathway and of gamma-cystathionase activity in the formation of cysteine and sulfate from methionine in rat hepatocytes. 211 6

The addition of L-cysteine to hepatic cytosols causes inactivation of tyrosine aminotransferase. We have studied the mechanism of inactivation and the effect of streptozotocin-induced diabetes in the rat on the inactivation of tyrosine aminotransferase in the presence of fractions prepared from livers and kidneys. Diabetes increased the rate at which tyrosine aminotransferase was inactivated after addition of cysteine to hepatic cytosols. The inactivation was due to the production of thiocysteine (which contains sulfane sulfur) from cystine as a result of desulfuration catalyzed by gamma-cystathionase. Diabetes increased the content of cystathionine beta-synthase and gamma-cystathionase in liver. As a result, cytosols from diabetic animals converted homocysteine, cystathionine, cysteine and cystine to sulfane at an elevated rate, with resulting inactivation of tyrosine aminotransferase. In contrast, inactivation in kidney fractions was not affected by diabetes. Incubation with an inhibitor of gamma-cystathionase (propargylglycine) prevented inactivation of tyrosine aminotransferase. These results show that the potential for the formation of sulfane sulfur by the enzymes of the transsulfuration pathway is enhanced by chronic diabetes.
...
PMID:Experimental diabetes increases the formation of sulfane by transsulfuration and inactivation of tyrosine aminotransferase in cytosols from rat liver. 256 58


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---