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

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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)

Various vitamin B6 enzymes play important roles in mammalian and microbial metabolism of selenium amino acids. Selenocysteine is synthesized from selenohomocysteine by catalysis of cystathionine beta-synthase and cystathionine gamma-lyase, which both require pyridoxal phosphate. Selenocysteine beta-lyase, a new B6-enzyme, exclusively catalyzes beta-elimination of selenocysteine, and occurs in mammalian systems and bacteria. Methionine gamma-lyase, cysteine desulfurase, cysteine sulfinate desulfinase, and D-selenocystine alpha,beta-lyase, which are B6-enzymes, act on cysteine, cysteine sulfinate, D-cystine, and their derivatives, and their selenium counterparts indiscriminately. Their reaction mechanisms are comparatively described.
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PMID:Vitamin B6 enzymes participating in selenium amino acid metabolism. 1060 91

Transcription of the genes for sulfur assimilation and methionine biosynthesis in Saccharomyces cerevisiae is regulated by the size of the intracellular pool of an organic sulfur compound. The identity of this compound is not clear, but suggestions include S-adenosylmethionine (SAM) and cysteine. By studying the repression of selected sulfur assimilation (MET) genes, we found that the ability to form cysteine from homocysteine is crucial for methionine-mediated repression to take place. The transcription of MET14 and MET25 could not be repressed by methionine in strains in which either STR4 (which encodes cystathionine beta-synthase) or STR1 (cystathionine gamma-lyase) was disrupted, whereas the repression was independent of GSH1 (which encodes the enzyme responsible for the first step in glutathione biosynthesis from cysteine). In contrast, cysteine could repress the MET genes in all of these strains. Two genes that presumably encode cystathionine gamma-synthase and cystathionine beta-lyase were identified by genetic disruption (ORFs YJR130c and YGL184c), yielding yeast strains that cannot convert cysteine into homocysteine. Repression by cysteine was possible in either disruptant, suggesting a role in repression for cysteine alone. While some repression of MET genes could be accomplished by homocysteine in a strain that cannot form SAM from methionine, a low intracellular level of SAM seems to be necessary for full cysteine-mediated repression to take place.
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PMID:Cysteine is essential for transcriptional regulation of the sulfur assimilation genes in Saccharomyces cerevisiae. 1082 Nov 89

The concentrations of sulfur-containing amino acids, taurine, cystathionine, methionine and cystine, as well as cystathionine beta-synthase and gamma-lyase activities in various tissues of Agkistrodon blomhoffi (mamushi) were measured. The concentration of taurine in examined tissues was greater than the concentration of other sulfur-containing amino acids. The concentration of cystathionine in various tissues was also much higher than those of methionine and cystine, but the concentration of cystathionine in the brain was lower than that of methionine. In all tissues examined in this study, cystathionine beta-synthase activity was much higher than that of cystathionine gamma-lyase. The ratios of cystathionine beta-synthase to gamma-lyase activities in various tissues were 5.6 to approximately 85.6. The concentration of sulfur-containing amino acids in muscle and skin divided into eight portions of the body were also determined. The concentrations of methionine and cystine in each portion of muscle and skin were almost the same, but the concentrations of taurine and cystathionine in each portion of the body were varied.
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PMID:Contents of sulfur amino acids, and cystathionine beta-synthase and gamma-lyase activities in various tissues from agkistroden blomhoffi (mamushi). 1097 44

An elevated plasma level of homocysteine is a risk factor for the development of cardiovascular disease. The purpose of this study was to investigate the effect of glucagon on homocysteine metabolism in the rat. Male Sprague-Dawley rats were treated with 4 mg/kg/day (3 injections per day) glucagon for 2 days while control rats received vehicle injections. Glucagon treatment resulted in a 30% decrease in total plasma homocysteine and increased hepatic activities of glycine N-methyltransferase, cystathionine beta-synthase, and cystathionine gamma-lyase. Enzyme activities of the remethylation pathway were unaffected. The 90% elevation in activity of cystathionine beta-synthase was accompanied by a 2-fold increase in its mRNA level. Hepatocytes prepared from glucagon-injected rats exported less homocysteine, when incubated with methionine, than did hepatocytes of saline-treated rats. Flux through cystathionine beta-synthase was increased 5-fold in hepatocytes isolated from glucagon-treated rats as determined by production of (14)CO(2) and alpha-[1-(14)C]ketobutyrate from l-[1-(14)C]methionine. Methionine transport was elevated 2-fold in hepatocytes isolated from glucagon-treated rats resulting in increased hepatic methionine levels. Hepatic concentrations of S-adenosylmethionine and S-adenosylhomocysteine, allosteric activators of cystathionine beta-synthase, were also increased following glucagon treatment. These results indicate that glucagon can regulate plasma homocysteine through its effects on the hepatic transsulfuration pathway.
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PMID:Hyperglucagonemia in rats results in decreased plasma homocysteine and increased flux through the transsulfuration pathway in liver. 1155 9

Schizosaccharomyces pombe, in contrast to Saccharomyces cerevisiae and Aspergillus nidulans, lacks cystathionine beta-synthase and cystathionine gamma-lyase, two enzymes in the pathway from methionine to cysteine. As a consequence, methionine cannot serve as an efficient sulphur source for the fungus and does not bring about repression of sulphur assimilation, which is under control of the cysteine-mediated sulphur metabolite repression system. This system operates at the transcriptional level, as was shown for the homocysteine synthase encoding gene. Our results corroborate the growing evidence that cysteine is the major low-molecular-weight effector in the regulation of sulphur metabolism in bacteria, fungi and plants.
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PMID:Sulphur amino acid synthesis in Schizosaccharomyces pombe represents a specific variant of sulphur metabolism in fungi. 1175 80

A 0.5 kb fragment of Streptomyces venezuelae ISP5230 genomic DNA was amplified by PCR using primers based on consensus sequences of cysteine synthase isozyme A from bacteria. The deduced amino acid sequence of the PCR product resembled not only cysteine synthase sequences from prokaryotes and eukaryotes but also eukaryotic cystathionine beta-synthase sequences. Probing an Str. venezuelae genomic library with the PCR product located a hybridizing colony from which pJV207 was isolated. Sequencing and analysis of the Str. venezuelae DNA insert in pJV207 detected two ORFs. The deduced amino acid sequence of ORF1 matched both cysteine synthase and cystathionine beta-synthase sequences in GenBank, but its size favoured assignment as a cystathionine beta-synthase. ORF2 in the pJV207 insert was unrelated in function to ORF1; in its sequence the deduced product resembled acetyl-CoA transferases, but disruption of the ORF did not cause a detectable phenotypic change. Disruption of ORF1 failed to elicit cysteine auxotrophy in wild-type Str. venezuelae, but in the cys-28 auxotroph VS263 it prevented restoration of prototrophy with homocysteine or methionine supplements. The change in phenotype implicated loss of the transsulfuration activity that in the wild-type converts these supplements to cysteine. This study concludes that disruption of ORF1 inactivates a cbs gene, the product of which participates in cysteine synthesis by transsulfuration. Enzyme assays of Str. venezuelae mycelial extracts confirmed the formation of cysteine by thiolation of O-acetylserine, providing the first unambiguous detection of this activity in a streptomycete. Enzyme assays also detected cystathionine gamma-synthase, cystathionine beta-lyase and cystathionine gamma-lyase activity in the extracts and showed that the substrate for cystathionine gamma-synthase was O-succinyl-homoserine. Based on assay results, the cys-28 mutation in Str. venezuelae VS263 does not inactivate the cysteine synthase gene but impairs expression in cultures grown in minimal medium.
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PMID:Biosynthesis of sulfur-containing amino acids in Streptomyces venezuelae ISP5230: roles for cystathionine beta-synthase and transsulfuration. 1210 1

Abnormal elevation of plasma methionine may result from several different genetic abnormalities, including deficiency of cystathionine beta-synthase (CBS) or of the isoenzymes of methionine adenosyltransferase (MAT) I and III expressed solely in nonfetal liver (MAT I/III deficiency). Classically, these conditions have been distinguished most readily by the presence or absence, respectively, of elevated plasma free homocystine, detected by amino acid chromatography in the former condition, but absent in the latter. During the present work, we have assayed methionine, S-adenosylmethionine, S-adenosylhomocysteine, total homocysteine (tHcy), cystathionine, N-methylglycine (sarcosine), and total cysteine (tCys) in groups of both MAT I/III- and CBS-deficient patients to provide more evidence as to their metabolite patterns. Unexpectedly, we found that MAT I/III-deficient patients with the most markedly elevated levels of plasma methionine also had elevations of plasma tHcy and often mildly elevated plasma cystathionine. Evidence is presented that methionine does not inhibit cystathionine beta-synthase, but does inhibit cystathionine gamma-lyase. Mechanisms that may possibly underlie the elevations of plasma tHcy and cystathionine are discussed. The combination of elevated methionine plus elevated tHcy may lead to the mistaken conclusion that an MAT I/III-deficient patient is instead CBS-deficient. Less than optimal management is then a real possibility. Measurements of plasma cystathionine, S-adenosylmethionine, and sarcosine should permit ready distinction between the 2 conditions in question, as well as be useful in several other situations involving abnormalities of methionine and/or homocysteine derivatives.
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PMID:Elevated plasma total homocysteine in severe methionine adenosyltransferase I/III deficiency. 1214 70

Hydrogen sulfide (H2S) is a well-known toxic gas with the smell of rotten eggs. Since the first description of the toxicity of H2S in 1713, most studies about H2S have been devoted to its toxic effects. Recently, H2S has been proposed as a physiologically active messenger. Three groups discovered that the brain contains relatively high concentrations of endogenous H2S. This discovery accelerated the identification of an H2S-producing enzyme, cystathionine beta-synthase (CBS) in the brain. In addition to the well-known regulators for CBS, S-adenosyl-L-methionine (SAM) and pyridoxal-5'-phosphate, it was recently found that Ca2+/calmodulin-mediated pathways are involved in the regulation of CBS activity. H2S is produced in response to neuronal excitation, and alters hippocampal long-term potentiation (LTP), a synaptic model for memory. can also regulate the release of corticotropin-releasing hormone (CRH) from hypothalamus. Another H2S producing enzyme, cystathionine gamma-lyase (CSE), has been identified in smooth muscle, and H2S relaxes smooth muscle in synergy with nitric oxide (NO). Recent progress in the study of H2S as a novel neuromodulator/transmitter in the brain is briefly reviewed.
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PMID:Hydrogen sulfide as a neuromodulator. 1239 53

Some strains of Saccharomyces cerevisiae have detectable activities of L-serine O-acetyltransferase (SATase) and O-acetyl-L-serine/O-acetyl-L-homoserine sulfhydrylase (OAS/OAH-SHLase), but synthesize L-cysteine exclusively via cystathionine by cystathionine beta-synthase and cystathionine gamma-lyase. To untangle this peculiar feature in sulfur metabolism, we introduced Escherichia coli genes encoding SATase and OAS-SHLase into S. cerevisiae L-cysteine auxotrophs. While the cells expressing SATase grew on medium lacking L-cysteine, those expressing OAS-SHLase did not grow at all. The cells expressing both enzymes grew very well without L-cysteine. These results indicate that S. cerevisiae SATase cannot support L-cysteine biosynthesis and that S. cerevisiae OAS/OAH-SHLase produces L-cysteine if enough OAS is provided by E. coli SATase. It appears as if S. cerevisiae SATase does not possess a metabolic role in vivo either because of very low activity or localization. For example, S. cerevisiae SATase may be localized in the nucleus, thus controlling the level of OAS required for regulation of sulfate assimilation, but playing no role in the direct synthesis of L-cysteine.
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PMID:Role of Saccharomyces cerevisiae serine O-acetyltransferase in cysteine biosynthesis. 1258 6

Alterations in hepatic metabolism of S-amino acids were monitored over one week in male rats treated with a single dose of ethanol (3 g/kg, ip). Methionine and S-adenosylhomocysteine concentrations were increased rapidly, but S-adenosylmethionine, cysteine, and glutathione (GSH) decreased following ethanol administration. Activities of methionine adenosyltransferase, cystathionine gamma-lyase and cystathionine beta-synthase were all inhibited. gamma-Glutamylcysteine synthetase activity was increased from t = 8 hr, but GSH level did not return to control for 24 hr. Hepatic hypotaurine and taurine levels were elevated immediately, but reduced below control in 18 hr. Changes in serum and urinary taurine levels were consistent with results observed in liver. Cysteine dioxygenase activity was increased rapidly, but declined from t = 24 hr. The results show that a single dose of ethanol induces profound changes in hepatic S-amino acid metabolism, some of which persist for several days. Ethanol not only inhibits the cysteine synthesis but suppresses the cysteine availability further by enhancing its irreversible catabolism to taurine, which would play a significant role in the depletion of hepatic GSH.
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PMID:Alterations in hepatic metabolism of sulfur-containing amino acids induced by ethanol in rats. 1262 41


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