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)

Four new mutations in the cystathionine beta-synthase (CBS) gene have been identified in Italian patients with homocystinuria. The first mutation is a G-to-A transition at base 374 in exon 3, causing an arginine-to-glutamic acid substitution at position 125 of the protein (R125Q). This mutation has been found in homozygosity in a patient partially responsive to pyridoxine treatment. The second mutation is a C-to-T transition at base 770 in exon 7, causing a threonine-to-methionine substitution at amino acid 257 of the protein (T257M). This mutation has been observed in homozygosity in a patient nonresponsive to the cofactor treatment. The third mutation, found in heterozygosity in a patient responsive to pyridoxine treatment, is an insertion of 68 bp in exon 8 at base 844, which introduces a premature termination codon. The fourth mutation is C-to-T transition in exon 2 at base 262, causing a proline-to-serine substitution at position 88 of the protein (P88S). This mutation is carried on a single allele in three affected sisters responsive to the cofactor treatment. In addition, six previously reported mutations (A114V, E131D, P145L, I278T, G307S, and A1224-2C) have been tested in 14 independent Italian families. Mutations A114V and I278T are carried by three and by seven independent alleles, respectively. The other four mutations--including G307S and A1224-2C, common among northern European patients--have not been detected.
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PMID:The molecular basis of homocystinuria due to cystathionine beta-synthase deficiency in Italian families, and report of four novel mutations. 776 55

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.
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PMID:Alteration in the phosphatidylcholine biosynthesis of rat liver microsomes caused by vitamin B6 deficiency. 776 14

Moderate hyperhomocysteinaemia has recently been established as an independent risk factor for atherothrombotic disease. It might be caused by heterozygosity for cystathionine beta-synthase deficiency, an enzyme involved in the conversion of methionine to cysteine through the transsulphuration pathway or by inherited thermolability of the enzyme which remethylates homocysteine into methionine. In chronic renal failure (CRF) homocysteine levels are significantly elevated at a relatively early stage. The normal kidney possibly plays an important role in homocysteine catabolism, which cannot be performed in CRF. Alternatively, decreased extrarenal catabolism can contribute to the hyperhomocysteinaemia in this disease state. Treatment with folic acid, 5 mg daily, significantly lowers homocysteine levels in chronic renal patients.
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PMID:Hyperhomocysteinaemia: a role in the accelerated atherogenesis of chronic renal failure? 778 27

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.
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PMID:Expression of human cystathionine beta-synthase in Escherichia coli: purification and characterization. 782 2

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

The fission yeast Schizosaccharomyces pombe has a unique organization of sulfur amino acid metabolism: it has two distinct O-acetylhomoserine sulfhydrylases (homocysteine synthases). Similar to Enterobacteriaceae, S. pombe lacks cystathionine beta-synthase and cystathionine gamma-lyase-the enzymes of the reverse transsulfuration pathway, by which methionine is readily metabolized to cysteine-a likely effector in the sulfur metabolite repression system. Consequently no repression of sulfate assimilation is observed when methionine is added to the growth medium.
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PMID:Sulfur amino acid metabolism in Schizosaccharomyces pombe: occurrence of two O-acetylhomoserine sulfhydrylases and the lack of the reverse transsulfuration pathway. 792 67

We investigated the nitrous oxide-induced inactivation of methionine synthase and the concurrent homocysteine (Hcy) export in mutant fibroblasts with defects in the homocysteine catabolizing enzyme, cystathionine beta-synthase, or in methionine synthase, which carries out homocysteine remethylation. The fibroblasts were incubated in various concentrations of methionine to create conditions favoring methionine conservation or catabolism. In cystathionine beta-synthase-deficient cells, high medium methionine partly protected the enzyme against inactivation, as previously found in normal fibroblasts. The Hcy export rate at low methionine levels was low (0.2-0.6 nmol/h/10(6) cells), and increased 2-3-fold at high methionine levels. Nitrous oxide enhanced Hcy export rate at low methionine, so that in the presence of nitrous oxide, the Hcy export became less dependent of methionine. In cb1G cells, the enzyme inactivation was moderate and independent of medium methionine. The Hcy export rate was intermediate (0.5-0.8 nmol/h/10(6) cells) at low methionine levels, and increased moderately (< 2-fold) at high methionine levels or following nitrous oxide exposure. In cb1E mutants, the enzyme activity was not affected by nitrous oxide, and the Hcy export was high (0.8-1.6 nmol/h/10(6) cells) and independent of methionine and nitrous oxide. These data suggest that Hcy remethylation and cystathionine beta-synthase activity are major determinants of Hcy export at low and high methionine, respectively. The low susceptibility of methionine synthase to nitrous oxide in the presence of high methionine or in cb1G or cb1E mutants is probably related to low catalytic turnover.
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PMID:Effect of methionine and nitrous oxide on homocysteine export and remethylation in fibroblasts from cystathionine synthase-deficient, cb1G, and cb1E patients. 813 95

Mild homocysteinemia occurs surprisingly often in patients with premature vascular disease. We studied the possible enzymatic sources of this mild hyperhomocysteinemia and the control of homocysteine levels in plasma by treatment of patients with the cofactors and cosubstrates of homocysteine catabolism. We assessed homocysteine metabolism in 131 patients who had premature disease in their coronary, peripheral, or cerebrovascular circulation by using a standard oral methionine-load test. Impaired homocysteine metabolism occurred in 28 patients. We assayed levels of the primary enzymes of homocysteine catabolism in cultured skin fibroblast extracts from 15 of these 28 patients. The patients' cystathionine beta-synthase levels (3.68 +/- 2.52 nmol/h per milligram of cell protein, mean +/- SD) were markedly depressed compared with those from 31 healthy adult control subjects (7.61 +/- 4.49, P < .001). The patients' levels of 5-methyltetrahydrofolate: homocysteine methyltransferase were normal. While betaine: homocysteine methyltransferase was not expressed in skin fibroblasts, 24-hour urinary betaine and N,N-dimethylglycine measurements were consistent with normal or enhanced remethylation of homocysteine by betaine: homocysteine methyltransferase in the 13 patients tested. When treated daily with choline and betaine, pyridoxine, or folic acid, there was a normalization of the postmethionine plasma homocysteine level in 16 of 19 patients. Our results indicate that mild homocysteinemia in premature vascular disease may be caused by either a folate deficiency or deficiencies in cystathionine beta-synthase activity. It does not necessarily involve deficiencies of either 5-methyltetrahydrofolate:homocysteine methyltransferase or betaine:homocysteine methyltransferase. Effective treatment regimens are also defined.
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PMID:Disordered methionine/homocysteine metabolism in premature vascular disease. Its occurrence, cofactor therapy, and enzymology. 836 9

Elevated circulating homocyst(e)ine is a risk factor for occlusive vascular disease. We explored whether elevated plasma homocyst(e)ine is associated with increased plasma lipid hydroperoxides that might trigger vascular disease. We obtained plasma containing high levels of homocyst(e)ine from four patients with a homozygous deficiency of cystathionine beta-synthase activity and also from four heterozygotes with a deficiency of this enzyme after an oral methionine load. The mean plasma non-protein-bound homocyst(e)ine level in all subjects was more than 11-fold higher than the mean normal fasting value. Levels of high density lipoprotein (HDL) cholesteryl ester hydroperoxides (CEOOH), normalized against the concentration of free cholesterol in HDL, were not elevated in our subjects (mean +/- SD, 0.0091 +/- 0.0061) compared with values for 14 fasting healthy donors (0.0164 +/- 0.0086). An inverse dependency was observed between plasma total homocyst(e)ine and HDL CEOOH (r = -0.78, p = 0.023). Also, the ubiquinol-10/ubiquinone-10 ratio in HDL, which is expected to fall during oxidative stress, increased with plasma homocyst(e)ine. Since HDL contains the majority of detectable plasma lipid hydroperoxides, of which CEOOHs are the most abundant, our data suggest that an elevated plasma homocyst(e)ine level does not enhance oxidative stress, increase the levels of lipid hydroperoxides in plasma, or generate vascular damage by this mechanism.
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PMID:Circulating lipid hydroperoxide levels in human hyperhomocysteinemia. Relevance to development of arteriosclerosis. 846 86

Homocysteine can be methylated to form methionine by the cobalamin- (Cbl) and folate-dependent enzyme, methionine synthase; serum levels of total homocysteine are elevated in greater than 95% of patients with either Cbl or folate deficiency. Homocysteine can also condense with serine to form cystathionine in a pyridoxal phosphate-dependent reaction catalyzed by cystathionine beta-synthase. Cystathionine is subsequently cleaved to cysteine and alpha-ketobutyrate by the pyridoxal phosphate-dependent enzyme gamma-cystathionase. To assess levels of cystathionine in Cbl and folate deficiency, we developed a new capillary gas chromatographic-mass spectrometric assay and measured cystathionine in the serum of normal subjects and patients with clinically confirmed deficiencies of these vitamins. The normal range for serum cystathionine was 65 to 301 nmol/L (median = 126 nmol/L) for 50 normal blood donors. In 30 patients with clinically confirmed Cbl deficiency, values for cystathionine ranged from 208 nmol/L to 2,920 nmol/L (median = 816 nmol/L) and 26 (87%) had levels above the normal range. In 20 patients with clinically confirmed folate deficiency, cystathionine concentrations ranged from 138 nmol/L to 4,150 nmol/L (median = 1,560 nmol/L) and 19 (95%) had values above the normal range. Five homozygotes for cystathionine beta-synthase deficiency had high values for serum-total homocysteine and low or low-normal values for serum cystathionine that ranged from 30 nmol/L to 114 nmol/L even though they were on treatment with pyridoxine and had partially responded. One patient with a defect in the synthesis of 5-CH3-tetrahydrofolate and five patients with defects in the synthesis of CH3-Cbl had high values for serum-total homocysteine and high values for cystathionine that ranged from 311 nmol/L to 1,500 nmol/L even though they were on treatment with folic acid and Cbl, respectively, and had partially responded. We conclude that levels of cystathionine are evaluated in the serum of most patients with Cbl and folate deficiency and that they are useful in the differential diagnosis of an elevated serum-total homocysteine level.
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PMID:Elevation of serum cystathionine levels in patients with cobalamin and folate deficiency. 850 76


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