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)

The neurologic complications of cystathionine beta-synthase deficiency are thought to be secondary to accumulation of homocyst(e)ine in the CNS. Treatment of this disorder with betaine has been shown to improve the behavior of individuals, to reduce plasma total homocysteine, and to correct secondary abnormalities of serine. To test the hypothesis that homocyst(e)ine accumulates within the CNS and that this can be reduced by treatment with betaine, we measured total homocysteine and related metabolites in the plasma of 10 children with cystathionine beta-synthase deficiency and cerebrospinal fluid of five children before and during betaine therapy. In plasma, betaine significantly lowered total homocysteine (but not to the normal range) and had a variable effect on methionine. In the cerebrospinal fluid, total homocysteine was raised before treatment (mean 1.2 microM) and was significantly reduced by betaine (mean 0.32 microM) but not to the normal range (<0.10 microM). Cerebrospinal fluid methionine was raised before and during treatment, but betaine did not cause a significant further increase. Cerebrospinal fluid serine was significantly reduced before treatment and rose to the normal range with betaine. Cerebrospinal fluid S-adenosylmethionine was normal before treatment and rose significantly with treatment; there were no significant changes in cerebrospinal fluid 5-methyltetrahydrofolate. The demonstration of accumulation of homocysteine within the CNS lends support to the hypothesis that this may be one cause of the neurologic complications of cystathionine beta-synthase deficiency. Betaine is effective in reducing cerebrospinal fluid homocysteine, but concentrations are still significantly raised during treatment.
...
PMID:Cerebrospinal fluid and plasma total homocysteine and related metabolites in children with cystathionine beta-synthase deficiency: the effect of treatment. 935 26

Epidemiological studies have provided strong evidence that an elevated plasma homocysteine concentration is an important independent risk factor for cardiovascular disease. We have shown, in the rat, that the kidney is a major site for the removal and subsequent metabolism of plasma homocysteine [Bostom, Brosnan, Hall, Nadeau and Selhub (1995) Atherosclerosis 116, 59-62]. To characterize the role of the kidney in homocysteine metabolism further, we measured the disappearance of homocysteine in isolated renal cortical tubules of the rat. Renal tubules metabolized homocysteine primarily through the transulphuration pathway, producing cystathionine and cysteine (78% of homocysteine disappearance). Methionine production accounted for less than 2% of the disappearance of homocysteine. Cystathionine, and subsequently cysteine, production rates, as well as the rate of disappearance of homocysteine, were sensitive to the level of serine in the incubation medium, as increased serine concentrations permitted higher rates of cystathionine and cysteine production. On the basis of enrichment profiles of cystathionine beta-synthase and cystathionine gamma-lyase, in comparison with marker enzymes of known location, we concluded that cystathionine beta-synthase was enriched in the outer cortex, specifically in cells of the proximal convoluted tubule. Cystathionine gamma-lyase exhibited higher enrichment patterns in the inner cortex and outer medulla, with strong evidence of an enrichment in cells of the proximal straight tubule. These studies indicate that factors that influence the transulphuration of homocysteine may influence the renal clearance of this amino acid.
...
PMID:Characterization of homocysteine metabolism in the rat kidney. 935 66

Cystathionine beta-synthase (CBS) deficiency is an autosomal recessive disorder which results in extremely elevated levels of total plasma homocysteine (tHcy) and high risk of thromboembolic events. About half of all patients diagnosed with CBS deficiency respond to pyridoxine treatment with a significant lowering of tHcy levels. We examined 12 CBS-deficient patients from 10 Norwegian families for mutations in the CBS gene and identified mutations in 18 of the 20 CBS alleles. Five of the seven patients classified as pyridoxine-responsive contain the newly identified point mutation, G797A (R266K). This point mutation is tightly linked with a previously identified 'benign' 68 bp duplication of the intron 7-exon 8 boundary within the CBS gene. We tested the effect of all of the mutations identified on human CBS function utilizing a yeast system. Five of the six mutations had a distinguishable phenotype in yeast, indicating that they were in fact pathogenic. Interestingly, the G797A allele had no phenotype when the yeast were grown in high concentrations of pyridoxine, but a severe phenotype when grown in low concentrations, thus mirroring the behavior in humans. These studies show that the G797A mutation is an important cause of pyridoxine-responsive CBS deficiency and demonstrate the utility of yeast functional assays in the analysis of human mutations.
...
PMID:Functional modeling of vitamin responsiveness in yeast: a common pyridoxine-responsive cystathionine beta-synthase mutation in homocystinuria. 936 Oct 25

Mildly elevated plasma homocysteine has been shown to be associated with an elevated risk for cardiovascular disease. In this study, we analyzed the frequency of a common 844ins68 insertion variant in the cystathionine beta-synthase gene (CBS) in patients with arterial occlusive disease and in controls and assessed the association between the insertion variant and plasma homocysteine concentrations. The insertion variant was equally distributed between both study groups. Furthermore, the presence of this insertion variant, either in the heterozygous or the homozygous state, is not associated with hyperhomocysteinemia. We therefore conclude that this common 844ins68 variant is a neutral insertion variant.
...
PMID:A common 844INS68 insertion variant in the cystathionine beta-synthase gene. 936 94

Cystathionine beta-synthase (CBS) catalyzes the irreversible, serine-dependent conversion of homocysteine to cystathionine via a transsulfuration pathway. CBS deficiency not only is the leading cause of homocystinuria, an inherited genetic disorder, but may contribute to cardiovascular disease as well. We isolated three new isoforms of human CBS mRNA from a human liver cDNA library. We designate these CBS mRNAs as CBS 3, CBS 4, and CBS 5, and the CBS mRNAs reported previously by Kraus et al. (1993) (Hum. Mol. Genet. 2, 1933-1938) and Kruger and Cox (1994) (Proc. Natl. Acad. Sci. USA 91, 6614-6618) as CBS 1 and CBS 2, respectively. Sequence analyses show that the only difference among the five CBS mRNAs is at the beginning of the 5'-untranslated region. Tissue distribution studies reveal that liver and pancreas have the highest amounts of CBS mRNAs. CBS mRNA is present in all regions of the brain tested. We also report the differential distribution of CBS mRNA isoforms in tissues, showing that pancreas contains all five CBS isoforms and the liver has four CBS mRNA isoforms, CBS 1-4. The kidney contains only CBS 1 and CBS 2. In human fetal tissues, CBS 2 is present in the liver and kidney. PCR-based quantitative analyses of CBS mRNA isoforms in human liver demonstrate that CBS 1 and CBS 2 are the major species, with CBS 2 being more abundant, while CBS 3-5 are the minor species. Furthermore, results from our human liver cDNA screening and primer extension experiments show that each of the five CBS transcripts begins with a different exon, suggesting that CBS gene transcription might be regulated by more than one promoter.
...
PMID:Identification and tissue distribution of human cystathionine beta-synthase mRNA isoforms. 946 25

We have screened a rat brain library to identify proteins which interact with the 5'-end of huntingtin (amino acids 1-171), including the polyglutamine tract, in the yeast two-hybrid system. We detected an interaction with cystathionine beta-synthase (CBS) [L-serine hydrolyase (adding homocysteine), EC 4.2.1.22], which was confirmed in vitro using His-tagged CBS expressed in Escherichia coli , which was able to specifically bind both rat and human full-length huntingtin. Neither normal nor expanded polyglutamine repeat alone interacted with CBS in the yeast two-hybrid system and nor did constructs containing SBMA or DRPLA with normal or expanded polyglutamine tracts. CBS therefore appears to bind specifically to huntingtin. CBS deficiency is associated with homocystinuria, which is known to affect various physiological systems, including the central nervous system. Homocysteine, one of the substrates of CBS, is known to accumulate in homocystinuria and is metabolized to homocysteate and homocysteine sulphinate, both known to be powerful excitotoxic amino acids. It has been suggested that Huntington's disease involves the action of excitotoxic amino acids and this interaction with CBS may suggest a mechanism for such excitotoxic damage.
...
PMID:Huntingtin interacts with cystathionine beta-synthase. 946 92

The mechanism by which homocysteine causes endothelial cell (EC) injury and/or dysfunction is not fully understood. To examine the stress-inducing effects of homocysteine on ECs, mRNA differential display and cDNA microarrays were used to evaluate changes in gene expression in cultured human umbilical-vein endothelial cells (HUVEC) exposed to homocysteine. Here we show that homocysteine increases the expression of GRP78 and GADD153, stress-response genes induced by agents or conditions that adversely affect the function of the endoplasmic reticulum (ER). Induction of GRP78 was specific for homocysteine because other thiol-containing amino acids, heat shock or H2O2 did not appreciably increase GRP78 mRNA levels. Homocysteine failed to elicit an oxidative stress response in HUVEC because it had no effect on the expression of heat shock proteins (HSPs) including HSP70, nor did it activate heat shock transcription factor 1. Furthermore homocysteine blocked the H2O2-induced expression of HSP70. In support of our findings in vitro, steady-state mRNA levels of GRP78, but not HSP70, were elevated in the livers of cystathionine beta-synthase-deficient mice with hyperhomocysteinaemia. These studies indicate that the activation of stress response genes by homocysteine involves reductive stress leading to altered ER function and is in contrast with that of most other EC perturbants. The observation that homocysteine also decreases the expression of the antioxidant enzymes glutathione peroxidase and natural killer-enhancing factor B suggests that homocysteine could potentially enhance the cytotoxic effect of agents or conditions known to cause oxidative stress.
...
PMID:Characterization of the stress-inducing effects of homocysteine. 957 70

Homocysteine is an independent risk factor for arteriosclerotic disease. Deficiency of cystathionine beta-synthase (CBS) is the major cause of inherited homocysteinemia. The CBS gene is 25-30 kbp long and encodes a subunit of 63 kDa. The active form of the enzyme is a homotetramer that contains one heme and one pyridoxal 5'-phosphate per each subunit. It can also bind 1 mol of S-adenosylmethionine per mol of subunit. To date, an analysis of 205 homocystinuric alleles has been performed and 64 mutations found. The best studied, relatively "homogeneous" patient populations are those of Ireland, Holland, and Italy. While the overall frequency of the two most frequent mutations is 24% for I278T and 31% for G307S, the breakdown between the countries varies greatly. For instance, the B6-nonresponsive G307S mutation accounts for > 70% alleles in Ireland and B6-responsive I278T mutation on the continent approaches 45%. In conclusion, further research is needed to define the mutations in individual countries to facilitate screening and genotype/phenotype correlations. Future biochemical studies will likely elucidate the role of heme in the enzyme and the tertiary structure of CBS.
...
PMID:Biochemistry and molecular genetics of cystathionine beta-synthase deficiency. 958 26

Moderate hyperhomocysteinaemia (MHH) is a risk factor for arteriosclerosis and thrombosis. About 10%-20% of the normal population have homocysteine levels contributing to an increased risk for arterial and venous disease. Main regulating enzymes of homocysteine metabolism are cystathionine beta-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR). Heterozygosity for CBS deficiency is most likely not an important cause for MHH in vascular disease. A recently discovered cause of MHH is reduced MTHFR activity due to a homozygous C677T mutation in the coding region of MTHFR. This mutation has been related to an increased risk for cardiovascular disease, although a number of studies are not confirmative. The elevated homocysteine levels due to this mutation can be normalized by administration of vitamins involved in homocysteine metabolism, in particular folate.
...
PMID:Mutated 5,10-methylenetetrahydrofolate reductase and moderate hyperhomocysteinaemia. 958 41

Mutations in cystathionine beta-synthase (CBS) are known to cause homocystinuria, a recessive disorder characterized by excessive levels of total homocysteine (tHcy) in plasma. The primary cause of mortality is thromboembolism induced by the excessive tHcy levels. Mild increases in tHcy levels are a significant risk factor in the development of vascular disease in the general population. This can result from heterozygosity at the CBS locus or polymorphic variation in other enzymes involved in homocysteine re-methylation. We report here that a mutation which deletes the carboxy-terminal 145 amino acids of CBS can functionally suppress the phenotype of several CBS mutant alleles found in homocystinurics when expressed in yeast. This C-terminal domain of CBS acts to inhibit enzymatic activity and is in turn regulated by S-adenosylmethionine (AdoMet), a positive effector of CBS. Our results indicate that most mutations found in homocystinurics do not cause dysfunction of the catalytic domain, but rather interfere with the activation of the enzyme. These findings suggest a new drug target to treat homocystinuria and homocysteine-related vascular disease.
...
PMID:Correction of disease-causing CBS mutations in yeast. 959 Feb 98


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

---