Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The steady-state kinetics of the two substrate reaction of L-cysteine desulfation in the presence of 2-mercaptoethanol catalyzed by serine sulfhydrase from bakers yeast -- a pyridoxal phosphate-containing enzyme of the beta -- substituting lyase type -- were studied. Highly purified enzyme preparations (approximately 90% purity) of Saccharomyces cerevisiae with specific activity of 25 mumoles of H2S per 1 hr per mg of protein were used. The values of V, KS1, KS2 and alpha were calculated from the initial rates of the reaction under constant concentration of L-cysteine (S1) and variable concentration of 2-mercaptoethanol (S2) and vice versa. The data obtained suggest that under conditions of a two-substrate reaction catalyzed by serine sulfhydrase and in case of beta-cyanoalanine synthase of blue lupin the substrate binding to the enzyme is interdependent and obeys a unordered mechanism with o formation of a ternary aminosubstrate-pyridoxal phosphateenzyme-cosubstrate complex (alpha = 2.6).
 ...
PMID:[Steady-state kinetics of reactions catalyzed by serine sulfhydrases of Saccharomyces serevisiae]. 38 Jun 61

Cystathionine beta-synthase has been purified from human liver more than 3000-fold by a series of steps including high speed centrifugation, ammonium sulfate fractionation, chromatography on hydroxylapatite and DEAE-cellulose, gel filtration, preparative polyacrylamide gel electrophoresis, and glycerol density gradient centrifugation. The enzyme obtained is homogeneous as judged by polyacrylamide gel electrophoresis in four different systems: native, isoelectric focusing, in sodium dodecyl sulfate, and in 8 M urea. The native enzyme has an estimated molecular weight of 94,000 and is composed of two apparently identical subunits of 48,000. The pure enzyme has a specific activity of 160 units/mg of protein and contains tightly bound cofactor, pyridoxal 5' -phosphate. It is possesses serine sulfhydrase as well as cystathionine synthase activity. It has a broad pH optimum from 8.4 to 9.0, apparent Km values for L-serine of 1.15 mM and for L-homocysteine of 0.59 mM, and a pI of 5.2 The enzyme is stable over a pH range from 6.5 to 8.0 in phosphate buffers and can be stored in 40% glycerol at -15 degrees C for at least 1 month.
 ...
PMID:Purification and properties of cystathionine beta-synthase from human liver. Evidence for identical subunits. 68 63

Theoretic and experimental arguments are surveyed which justify the setting up, within the family of pyridoxal-P-dependent lyases, of a special subgroup that comprizes several enzymes catalyzing exclusively beta-replacement reactions of alpha-aminoacids with electronegative substituents in the beta-position. The authors and their associates have studied the physico-chemical and catalytic properties of four high purity enzymes belonging to this subgroup, namely: cysteine lyase (EC 4.1.1.10) from embryonic chicken yolk-sac, serine sulfhydrase from chicken liver and the closely analogous or synonymic cystathionine beta-synthase (EC 4.4.1.8) from rat liver, and beta-cyanoalanine synthase (EC 4.4.1.9) from lupine seedlings, in comparison with some pyridoxal-P-requiring lyases differing in reaction specificity, for example, gamma-specific, alphabeta-eliminating or plurifunctional lyases such as gamma-cystathionase (EC 4.4.1.1) of animal tissues. The results of these studies, relating to subtrate and cosubstrate specificities of the enzymes mentioned, their interactions with some selective inhibitors, catalysis of isotopic exchange of hydrogen atoms in substrates and substrate analogs, etc., indicate that lyases of the exclusively beta-replacing type substantially differ in reaction mechanism from other subgroups of this enzyme family. Thus, it appears highly improbable that transient formation of an alphabeta-unsaturated, coenzyme-substrate imine, considered as an obligatory step in the action of lyases in the alphabeta-eliminating and other subgroups, should occur in the sequences of reaction intermediates in the case of beta-replacing lyases. Suggested features of the presumable catalytic mechanism of these lyases are discussed, such as : fixed conformation of the aminoacid substrate in the ES complex (protein-bound pyridoxal-P aldimine), with beta-substituent in orientation cis (rather than trans) to the Halpha atom ; role of the binding of appropriate cosubstrates (nucleophilic replacing agent, Cs) inducing essential electronic and/or steric transitions in the catalytic site of the ternanry CsES complexes, etc.
 ...
PMID:The pyridoxal-phosphate-dependent enzymes exclusively catalyzing reactions of beta-replacement. 78 60

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

Characterization of the physical and catalytic properties of the enzyme responsible for nematode "activated L-serine sulfhydrase" activity (L-cysteine + R-SH-->cysteine thioether + H2S) has led to its identification as a novel, variant form (allelozyme) of cystathionine beta-synthase that is distinct from a mammalian-type synthase also present in nematodes. Additional work has demonstrated the ability of live Panagrellus redivivus to produce H2[35S] from exogenous L-[35S]cysteine and 2-mercaptoethanol, thus providing preliminary evidence for the in vivo operation of the activated L-serine sulfhydrase reaction in nematodes.
 ...
PMID:The identification of a variant form of cystathionine beta-synthase in nematodes. 149 73

We determined the molecular basis of cystathionine beta-synthase (CBS) deficiency in three siblings with pyridoxine responsive homocystinuria using a significantly improved mutation screening method in bacteria. The phenotypic expression of the siblings differed even though their CBS genotypes were identical. The paternal allele contained a linked pair of mutations, C233G and G306C, corresponding to P78R and K102N in the polypeptide chain. Together, these inactivated the enzyme; however, expressed separately, they reduced activity by about one half. The single maternal mutation G715A (E239K) effectively abolished CBS activity. Subunits of CBS were absent from patient fibroblast extracts; however, E. coli, transformed with plasmids containing patient CBS cDNA, expressed the subunits, although in reduced amounts. The mother, an obligate heterozygote, was free from all signs of homocystinuria; nonetheless, extracts of her fibroblasts were devoid of CBS protein and activity. We conclude that fibroblast levels of CBS are only partially effective as prognosticators of disease severity and that it is important to test the in vivo response to vitamin B6 in all cases of homocystinuria, including those in which the mutations lead to the absence of the enzyme in cultured fibroblasts.
 ...
PMID:Identical genotypes in siblings with different homocystinuric phenotypes: identification of three mutations in cystathionine beta-synthase using an improved bacterial expression system. 798 78

Human cystathionine beta-synthase (CBS; EC 4.2.1.22) deficiency results in a recessive genetic disorder whose clinical and biochemical manifestations vary greatly among affected individuals. In an effort to identify and analyze mutations in the human CBS gene, we have developed a yeast expression system for human CBS. We have cloned and sequenced a human cDNA that codes for CBS and have expressed the human CBS protein in yeast cells lacking endogenous CBS. The human enzyme produced in yeast is functional both in vitro and in vivo. We have also cloned and sequenced the yeast gene, CYS4, that codes for CBS. The predicted human and yeast CBS proteins are 38% identical and 72% similar to each other, as well as sharing significant similarity with bacterial cysteine synthase. These results demonstrate the evolutionary conservation of CBS and establish the utility of a yeast expression system for studying human CBS.
 ...
PMID:A yeast system for expression of human cystathionine beta-synthase: structural and functional conservation of the human and yeast genes. 802 26

Mutations in the human cystathionine beta-synthase (CBS) gene are known to cause homocystinuria and may also be a significant risk factor for premature atherosclerosis. We have previously shown that the human CBS protein can substitute for the endogenous yeast CBS protein in Saccharomyces cerevisiae. We now show that expression of three different CBS mutants known to be associated with reduced enzyme activity in humans fail to complement growth in the yeast assay. In addition, we have used the yeast CBS assay to identify eight mutant CBS alleles in cell lines from patients with CBS deficiency. These mutant alleles include two previously identified and five novel CBS mutations. Our results also demonstrate that the yeast CBS assay can detect a large percentage of individuals heterozygous for mutations in CBS. This system should be useful in determining the relationship between CBS mutations and human disease.
 ...
PMID:A yeast assay for functional detection of mutations in the human cystathionine beta-synthase gene. 852 2

RT-PCR and direct sequence analyses were used to define mutations in the cystathionine beta-synthase (CBS) gene in two unrelated male patients with vitamin B6 nonresponsive homocystinuria. Both patients were compound heterozygotes for CBS alleles containing point mutations. One patient had a maternally derived G->A transition in the splice-donor site of intron 1, resulting in aberrant splicing of CBS mRNA. The other allele contained a missense mutation resulting in the previously reported E144K mutant CBS protein. The second patient had a maternally derived 4 bp insertion in exon 17, predicted to cause a CBS peptide of altered amino acid sequence. A 494G->A transition was found in exon 4 of the other allele, predicting a C165Y substitution. Expression of recombinant CBS protein, containing the C165Y mutation, had no detectable catalytic activity. Each mutation was confirmed in genomic DNA.
 ...
PMID:Mutational analysis of the cystathionine beta-synthase gene: a splicing mutation, two missense mutations and an insertion in patients with homocystinuria. Mutations in brief no. 120. Online. 1021 8

At least some mammalian tissues produce H2S in vitro from L-cysteine at rates sufficient to have physiological effects. To determine whether tissues of macrofaunal invertebrates have the same capacity, we measured H2S production in tissue homogenates of the Manila clam Tapes philippinarum and the lugworm Arenicola marina. Tissue homogenates from both animals produced significant quantities of H2S gas upon addition of L-cysteine and the enzyme cofactor pyridoxal-5PRIME;-phosphate (10 mmol l(-1) and 2 mmol l(-1), respectively), while only tissues from T. philippinarum produced measurable H2S in the absence of added substrate or cofactor. In T. philippinarum tissues, H2S production was completely inhibited by the cystathionine beta-synthase (CBS) inhibitor aminooxyacetic acid (AOAA), suggesting that the majority of H2S production was via CBS pathways, while in A. marina body wall, AOAA inhibited only half of the total H2S production, indicating that the CBS pathway was not the only major source of H2S production. H2S production in tissues of T. philippinarum but not A. marina was doubled by the addition of a second thiol substrate (2.5 mmol l(-1) 2-mercaptoethanol), suggesting the presence of an 'activated serine sulfhydrase pathway', which had previously been demonstrated only in some microfauna.
 ...
PMID:Enzymatic hydrogen sulfide production in marine invertebrate tissues. 1216 Aug 76


1 2 Next >>