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)

Twenty-nine amino acids were analyzed in the sera of 105 adult Senegambian goitrous patients classified as stages I, II, and III according to World Health Organization recommendations. Mean serum concentration of all essential amino acids revealed highly significant drops (p less than 0.001) as goiter stage increased, except for methionine (Met). Most nonessential amino acids (NEAA) and intermediary metabolites were similarly characterized by a general decrease to the subnormal range, although some resisted depression in stages II and III. Homocystine (Hcy) demonstrated a unique pattern in that it was the only NEAA distinguished by regularly rising serum levels. These data are consistent with the view that endemic goiter is associated with overall stepwise downregulation in protein metabolism. In addition to iodine restriction, generalized malnutrition may aggravate the goitrogenic processes. Serum levels of Met and Hcy strongly suggest that the first step of the transsulfuration pathway is impaired in protein-depleted states due to cystathionine beta-synthase (EC 4.2.1.22) deficiency.
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PMID:Nutritional significance of alterations in serum amino acid patterns in goitrous patients. 308 Aug 69

Two separate metabolic pathways that methylate homocysteine to methionine are known in humans, utilizing, respectively, 5-methyltetrahydrofolate and betaine as methyl donors. Deficiency of the folate-dependent methylation system is linked to hyperhomocysteinemia. Our data suggest that this deficiency leads to concurrent metabolic down-regulation of homocysteine transsulfuration that may contribute to hyperhomocysteinemia. By contrast, no instances have been reported of hyperhomocysteinemia resulting from deficiencies of betaine-dependent homocysteine methylation. Long-term betaine supplementation of 10 patients, who had pyridoxine-resistant homocystinuria and gross hyperhomocysteinemia due to deficiency of cystathionine beta-synthase activity, caused a substantial lowering of plasma homocysteine, which has now been maintained for periods of up to 13 years. Betaine had to be taken regularly because the effect soon disappeared when treatment was stopped. In conclusion, depressed activity of the transsulfuration pathway may contribute to hyperhomocysteinemia because of primary deficiencies of enzymes of either the transsulfuration or of the folate-dependent methylation pathways. Stimulation of betaine-dependent homocysteine remethylation causes a commensurate decrease in plasma homocysteine that can be maintained as long as betaine is taken.
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PMID:Human homocysteine catabolism: three major pathways and their relevance to development of arterial occlusive disease. 864 74

The major cause of homocystinuria is mutation of the gene encoding the enzyme cystathionine beta-synthase (CBS). Deficiency of CBS activity results in elevated levels of homocysteine as well as methionine in plasma and urine and decreased levels of cystathionine and cysteine. Ninety-two different disease-associated mutations have been identified in the CBS gene in 310 examined homocystinuric alleles in more than a dozen laboratories around the world. Most of these mutations are missense, and the vast majority of these are private mutations. The two most frequently encountered of these mutations are the pyridoxine-responsive I278T and the pyridoxine-nonresponsive G307S. Mutations due to deaminations of methylcytosines represent 53% of all point substitutions in the coding region of the CBS gene.
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PMID:Cystathionine beta-synthase mutations in homocystinuria. 1033 90

Deficiency of cystathionine beta-synthase (CBS) is the commonest cause of primary homocystinuria. Homocysteine metabolism is intimately linked with the metabolism of folate, vitamin B12 (cobalamin) and pyridoxine. It is hypothesised that the pathogenesis of neuropsychiatric manifestations in homocystinuria, folate and cobalamin deficiencies are related to imbalance neurotransmitters in the CNS through disturbances in the pathways linking the metabolism of homocysteine and these vitamins. Although neuropsychiatric disorders are relatively common among patients with homocystinuria, it is not well recognised as the causative factor among patients presenting with neuropsychiatric disorders. A 31 year old woman presented with a three week history of delirium and inappropriate and labile affect. There was no history suggestive of drug or alcohol abuse, nutritional deficiency or organic disorders. EEG, cerebral CT, MRI and microbiological investigations did not reveal any organic causes. Because of a diagnosis of pyridoxine-responsive homocystinuria seven years previously, the possibility of homocystinuria was considered and investigated. Laboratory tests revealed macrocytosis and a high concentration of urinary total homocystine. Commencement of pyridoxine at 400 mg/day resulted in disappearance of homocystine in urine within four days with remarkable clinical improvement. Homocystinuria should be considered in the differential diagnosis of unexplained neuropsychiatric disorders in patients who have past or family history of homocystinuria, mental retardation, thromboembolic episodes, vascular diseases or clinical and laboratory features resembling folate and/or vitamin B12 deficiencies. Homocystinuria-associated neuropsychiatric disturbances can easily be treated with pyridoxine in 50% of cases.
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PMID:Homocystinuria and psychiatric disorder: a case report. 1050 67

Cystathionine beta-synthase (CBS) is a unique heme enzyme that catalyzes a PLP-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an autosomal recessively inherited disease of sulfur metabolism. A truncated form of CBS in which the C-terminal amino-acid residues have been deleted has been prepared. The truncated CBS subunits form a dimer, in contrast to the full-length subunits which form tetramers and higher oligomers. The truncated CBS yielded crystals diffracting to 2.6 A which belong to space group P3(1) or P3(2). This is the first comprehensive structural investigation of a PLP and heme-containing enzyme.
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PMID:Crystallization and preliminary X-ray diffraction analysis of the active core of human recombinant cystathionine beta-synthase: an enzyme involved in vascular disease. 1117 83

Cystathionine beta-synthase (CBS) is a unique heme- containing enzyme that catalyzes a pyridoxal 5'-phosphate (PLP)-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an inherited disease of sulfur metabolism characterized by increased levels of the toxic metabolite homocysteine. Here we present the X-ray crystal structure of a truncated form of the enzyme. CBS shares the same fold with O-acetylserine sulfhydrylase but it contains an additional N-terminal heme binding site. This heme binding motif together with a spatially adjacent oxidoreductase active site motif could explain the regulation of its enzyme activity by redox changes.
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PMID:Structure of human cystathionine beta-synthase: a unique pyridoxal 5'-phosphate-dependent heme protein. 1148 94

It has been known for decades that babies born to women that have a dietary deficiency in folic acid (folate) are at increased risk for birth defects, and that the nervous system is particularly susceptible to such defects. Folate deficiency in adults can increase risk of coronary artery disease, stroke, several types of cancer, and possibly Alzheimer's and Parkinson's diseases. Recent findings have begun to reveal the cellular and molecular mechanisms whereby folate counteracts age-related disease. An increase in homocysteine levels is a major consequence of folate deficiency that may have adverse effects on multiple organ systems during aging. Humans with inherited defects in enzymes involved in homocysteine metabolism, including cystathionine beta-synthase and 5,10-methylenetetrahydrofolate reductase, exhibit features of accelerated aging and a marked propensity for several age-related diseases. Homocysteine enhances accumulation of DNA damage by inducing a methyl donor deficiency state and impairing DNA repair. In mitotic cells such DNA damage can lead to cancer, while in postmitotic cells such as neurons it promotes cell death. The emerging data strongly suggest that elevated homocysteine levels increase the risk of multiple age-related diseases, and point to dietary supplementation with folate as a primary means of normalizing homocysteine levels and increasing healthspan.
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PMID:Folic acid and homocysteine in age-related disease. 1203 51

Cystathionine beta-synthase (CBS) is a unique heme-containing enzyme that catalyses a pyridoxal 5'-phosphate (PLP)-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an inherited disease of sulfur amino acid metabolism characterised by increased levels of homocysteine and methionine and decreased levels of cysteine. Presently, more than 100 CBS mutations have been described which lead to homocystinuria with different degrees of severity in the patients. We have recently solved the crystal structure of a truncated form of this enzyme, which enables us to correlate some of these mutations with the structure.
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PMID:Structural insights into mutations of cystathionine beta-synthase. 1268 34

Recent studies suggest that apart from nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H2S) is another inorganic gaseous mediator in the cardiovascular system. H2S is synthesized from L-cysteine by either cystathionine beta-synthase (CBS) or cystathionin gamma--lyase (CSE), both using pyridoxal 5'-phosphate (vitamin B6) as a cofactor. CBS is the main H2S-producing enzyme in the brain and CSE is involved in H2S formation in the cardiovascular system. H2S induces hypotension in vivo and vasodilation vitro by opening KATP channels in vascular smooth muscle cells. Chronic administration of CSE inhibitor induces arterial hypertension in the rat. In addition, decreased H2S generation has been demonstrated in the vasculature of spontaneously hypertensive rat, in experimental hypertension induced by NO synthase blockade, and in hypoxia-induced pulmonary hypertension, and administration of exogenous H2S donor has significant therapeutic effects in these models. Deficiency of H2S may contribute to atherogenesis in some patients with hyperhomocysteinemia, in whom the metabolism of homocysteine to cysteine and H2S is compromised by vitamin B6 deficiency. Reduced H2S production in the brain was observed in patients with Alzheimer's disease. On the other hand, excess of H2S may lead to mental retardation in patients with Down's syndrome and may be involved in the pathogenesis of hypotension associated with septic shock.
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PMID:[Hydrogen sulfide as a biologically active mediator in the cardiovascular system]. 1528 Jul 98

Elevated plasma homocysteine has been linked to pregnancy complications and developmental diseases. Whereas hyperhomocysteinemia is frequently observed in populations at risk of malnutrition, hypoxia may alter the remethylation of homocysteine in hepatocytes. We aimed to investigate the combined influences of early deficiency in nutritional determinants of hyperhomocysteinemia and of neonatal hypoxia on homocysteine metabolic pathways in developing rats. Dams were fed a standard diet or a diet deficient in vitamins B12, B2, folate, month, and choline from 1 mo before pregnancy until weaning of the offspring. The pups were divided into four treatment groups corresponding to "no hypoxia/standard diet," "hypoxia (100% N2 for 5 min at postnatal d 1)/standard diet," "no hypoxia/deficiency," and "hypoxia/deficiency," and homocysteine metabolism was analyzed in their liver at postnatal d 21. Hypoxia increased plasma homocysteine in deficient pups (21.2 +/- 1.6 versus 13.3 +/- 1.2 microM, p < 0.05). Whereas mRNA levels of cystathionine beta-synthase remained unaltered, deficiency reduced the enzyme activity (48.7 +/- 2.9 versus 83.6 +/- 6.3 nmol/h/mg, p < 0.01), an effect potentiated by hypoxia (29.4 +/- 4.7 nmol/h/mg, p < 0.05). The decrease in methylene-tetrahydrofolate reductase activity measured in deficient pups was attenuated by hypoxia (p < 0.05), and methionine-adenosyltransferase activity was slightly reduced only in the "hypoxia/deficiency" group (p < 0.05). Finally, hypoxia enhanced the deficiency-induced drop of the S-adenosylmethionine/S-adenosylhomocysteine ratio, which is known to influence DNA methylation and gene expression. In conclusion, neonatal hypoxia may increase homocysteinemia mainly by decreasing homocysteine transsulfuration in developing rats under methyl-deficient regimen. It could therefore potentiate the well-known adverse effects of hyperhomocysteinemia.
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PMID:Mild neonatal hypoxia exacerbates the effects of vitamin-deficient diet on homocysteine metabolism in rats. 1584 41


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