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)

Four enzymes necessary for the metabolism of methionine by the trans-sulfuration pathway, methionine adenosyltransferase (EC 2.5.1.6), adenosylhomocysteinase (EC 3.3.1.1), cystathionine beta-synthase (EC 4.2.1.22) and cystathionine gamma-lyase (EC 4.4.1.1) were identified in Tetrahymean pyriformis. The ability of these cells to transfer 35S from E135S]methionine to form [35S] cysteine was also observed and taken as direct evidence for the functional existence of this pathway in Tetrahymena. An intermediate in the pathway and an active methyl donor, S-adenosylmethionine, was qualitatively identified in Tetrahymena and its concentration was found to be greater in late stationary phase cells than in early stationary phase cells.
...
PMID:The transsulfuration pathway in Tetrahymena pyriformis. 1 63

Trypsin causes an activation of serine sulfhydrase in the liver extracts from intact animals, but inhibits enzyme activity in the liver of ethionine treated rats. Trypsin also decreases an elevation of serine sulfhydrase activity caused by S-adenosylmethionine.
...
PMID:Effect of trypsin, S-adenosylmethionine and ethionine on L-serine sulfhydrase activity. 89 94

The gene for rat cystathionine beta-synthase consists of 17 exons. Its transcripts are alternatively spliced, forming four distinct mRNA species. Type III consists of exons 1 through 12, 14, 15, and 17; type I also contains exon 16. The open reading frame of type IV spans exons 1-->13; type II, 3-->13. We cloned the corresponding cDNAs into appropriate expression vectors and inserted the constructs into Escherichia coli (I, III, and IV) and Chinese hamster (CH) cells (I through IV); all sequences were transcribed and translated. Catalytic activity was observed only for types I and III in lysates of transfected CH cells and transformed E. coli. The catalytic and kinetic properties of I and III were identical despite their structural difference (exon 16). Both isoforms exhibited 6 mM Km constants for homocysteine which were reduced approximately eightfold by AdoMet; this elucidates the mechanism by which AdoMet regulates synthase activity. The four isoforms were differentially degraded by transfected cultured cells. Type III (t1/2 = 18 h) was degraded at 1/3 the rate of type I (t1/2 = 6 h); thus the 14 amino acid residues encoded by exon 16 appear to enhance degradation of CBS. The half-lives of both types II and IV were markedly shorter (ca. 1 h). Western blots comparing rat liver to lysates from transfected CH cells revealed that hepatocytes express both isoforms. Type III was predominant, as predicted by its longer half-life and more abundant mRNA. PCR analysis of cDNA from various tissues revealed that type III mRNA was preferred in liver, kidney, and heart; equal amounts of I and III were found in brain.
...
PMID:Rat cystathionine beta-synthase: expression of four alternatively spliced isoforms in transfected cultured cells. 138 33

A clinically benign form of persistent hypermethioninaemia with probable dominant inheritance was demonstrated in three generations of one family. Plasma methionine concentrations were between 87 and 475 mumol/L (normal mean 26 mumol/L; range 10-40 mumol/L); urinary methionine and homocystine concentrations were normal. Plasma homocystine, cystathionine, cystine and tyrosine were virtually normal. The concentrations in serum and urine of metabolites formed by the methionine transamination pathway were normal or moderately elevated. Methionine loading of two affected family members revealed a diminished ability to catabolize methionine, but the activities of methionine adenosyltransferase and cystathionine beta-synthase were not decreased in fibroblasts from four affected family members. Fibroblast methylenetetrahydrofolate reductase activity and its inhibition by S-adenosylmethionine were also normal, indicating normal regulation of N5-methyltetrahydrofolate-dependent homocysteine remethylation. Serum folate concentrations were not increased. The findings in this family differ from those previously described for known defects of methionine degradation. Since the hepatic and fibroblast isoenzymes of methionine adenosyltransferase differ in their genetic control, this family's biochemical findings appear consistent with a mutation in the structural gene for the hepatic methionine adenosyltransferase isoenzyme.
...
PMID:Persistent hypermethioninaemia with dominant inheritance. 152 87

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

Using an in vitro system which contained enzymes, substrates, and other reactants at concentrations which approximated the in vivo conditions in rat liver, we measured the simultaneous product formation by three enzymes which utilize homocysteine. In the control system, 5-methyltetrahydrofolate homocysteine methyltransferase, betaine homocysteine methyltransferase, and cystathionine beta-synthase accounted for 27, 27, and 46%, respectively, of the homocysteine consumed. Subsequent studies demonstrated that the adaptation from a high protein diet to a low protein diet is achieved by a significant increase in betaine homocysteine methyltransferase, and 83% reduction in cystathionine synthase, and a total decrease of 55% in the consumption of homocysteine. S-Adenosylmethionine, by activating cystathionine synthase, contributes significantly to the regulation of the pathway.
...
PMID:Methionine metabolism in mammals. Distribution of homocysteine between competing pathways. 674 58

Hyperhomocysteinemia occurs in approximately 30% of the patients with premature occlusive arterial disease (POAD). Some of these exhibit significantly reduced fibroblast cystathionine beta-synthase (CBS) activities, suggesting that they may be heterozygous for CBS deficiency. To test this possibility, we studied cDNA derived from four well characterized patients with POAD, exhibiting hyperhomocysteinemia and reduced CBS activities, from four normal controls, and from four obligatory heterozygotes for CBS deficiency. Lysates of individual colonies of E.coli, containing full-length PCR-amplification products in the expression vector, pKK388.1, were tested for CBS activity. cDNA from at least seven of the eight possible independent POAD alleles encoded catalytically active, stable CBS which exhibited normal response to both PLP and AdoMet. The sequences of all 3'-untranslated regions of all seven isolated POAD alleles were identical to the normal, 'wild-type' CBS sequences. The results of the expression studies were confirmed for one POAD patient by determining the full-length cDNA sequences for both alleles; these were entirely normal over the complete length of the cDNA. In contrast, the screening method correctly distinguished mutant from normal alleles in all four obligatory heterozygotes studied. We conclude that CBS mRNAs from POAD individuals are free from inactivating mutations, including all 33 previously identified in heterozygous carriers and homocystinuric patients.
...
PMID:Hyperhomocysteinemia in premature arterial disease: examination of cystathionine beta-synthase alleles at the molecular level. 763 11

Rats fed with a vitamin B6-deficient 70% casein diet for 5 weeks were found to have decreased considerably in the content of phosphatidylcholine (PC) in liver microsomes, presumably because of the depressed PC biosynthesis from choline or phosphatidylethanolamine (PE). The activities of choline phosphokinase and choline phosphotransferase in liver decreased, apparently, as compared with the pair-fed control or control rats. The hepatic level of the PE methyltransferase co-substrate, S-adenosylmethionine (SAM), decreased about 1/3, but the level of the inhibitory metabolite, S-adenosylhomocysteine (SAH), was elevated due to the marked reduction in the activities of cystathionine beta-synthase and gamma-cystathionase. The resultant molar ratio of SAM/SAH decreased drastically such that the methylation of PE to PC was decreased in vivo, as confirmed by lowering the activity of PE methyltransferase in vitro in response to a decreased molar ratio of SAM/SAH. A similar effect on the PE methylation was also observed in the pair-fed control rats, but the PC biosynthesis from choline clearly compensated for the drop of PC biosynthesis from PE. Results of this study demonstrate that vitamin B6 deficiency modified methionine metabolism and decreased choline utilization, and thus indirectly affected the biosynthesis of PC in liver microsomes.
...
PMID:Alteration in the phosphatidylcholine biosynthesis of rat liver microsomes caused by vitamin B6 deficiency. 776 14

Cystathionine beta-synthase (CBS) purification from mammalian tissues is complicated by proteolysis and enzyme aggregation. To surmount these difficulties, we cloned human CBS cDNA in tandem with the beta-galactosidase sequence of the fusion vector, pAX5-, then expressed the fusion protein, beta-galactosidase/CBS, in transformed Escherichia coli cells. Proteolytic treatment of the ammonium sulfate fraction of bacterial lysates with endoproteinase Xa liberated CBS which could then be separated from its fusion partner by DEAE-cellulose chromatography. This nearly homogeneous enzyme preparation was purified 140-fold over the crude bacterial lysate with nearly 50% recovery, and its specific activity, 210 U/mg protein, was comparable to that purified from human liver. The purified enzyme contained pyridoxal 5'-phosphate and exhibited positive cooperativity toward S-adenosyl-L-methionine (Hill coefficient = 5.2; Kact = 34 microM). Km values of the cloned enzyme in the absence of AdoMet are 3.1 and 1.1 mM for serine and homocysteine, respectively. They are virtually identical to those from human hepatic CBS. A Soret absorbance band (lambda max = 428 nm) which shifted to 448 nm after reduction with sodium dithionite revealed the presence of heme in the enzyme. Expression of the fusion protein in E. coli with subsequent purification represents the first time this enzyme has been isolated in sufficient quantities for biophysical and biochemical investigation.
...
PMID:Expression of human cystathionine beta-synthase in Escherichia coli: purification and characterization. 782 2

Cystathionine beta-synthase (CBS) deficiency is the most common cause of homocystinuria in humans. The human gene maps to chromosome 21q22.3 and encodes the CBS subunit of 551 amino acid residues (63kDa). CBS, a tetramer of these subunits, binds its two substrates, homocysteine and serine, and three additional ligands: pyridoxal 5'-phosphate, S-adenosylmethionine, and haem. Screening for mutations by expressing patient cDNA segments in E. coli permitted us to separate the parental CBS alleles, localize each mutation within one third of the cDNA, and functionally analyse the mutant protein. Using this method we identified the first 14 mutations in homocystinuria. The most common mutation in patients of predominantly 'Celtic' origin is the G919A transition which substitutes serine for glycine 307.
...
PMID:Komrower Lecture. Molecular basis of phenotype expression in homocystinuria. 796 89


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

---