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)

The effect of lactation on a number of enzymes involved in transmethylation reactions and the secretion of major methyl compounds into milk have been examined in sheep. The activities of hepatic phospholipid methyltransferase and 5-methyltetrahydrofolate-homocysteine methyltransferase were significantly higher in lactating ewes, compared with those in non-lactating ewes, while the activity of both hepatic and pancreatic glycine methyltransferase was significantly lower in the lactating state. No differences were observed in the activities of hepatic guanidoacetate methyltransferase, betaine-homocysteine methyltransferase and cystathionine beta-synthase on lactation. These results suggest that the extra demand for methyl groups for the secretion of methyl compounds in the milk is facilitated by enhancing the rate of de novo methyl group synthesis and lowering the rate of physiologically nonessential methylation.
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PMID:Regulation of methyl group metabolism in lactating ewes. 406 54

Cystathionine beta-synthase [L-serine hydrolyase (adding homocysteine), EC 4.2.1.22] was studied in cultured skin fibroblasts from two control subjects and three patients with pyridoxine-responsive homocystinuria. In crude cell sonicates, cystathionine synthase activity detected in each mutant line was less than 5% of control values. After differential centrifugation, ammonium sulfate fractionation, and calcium phosphate gel treatment, the specific activity of synthase from control lines increased 5- to 7-fold with 70-79% yield. These same steps led to only 2- to 3-fold purification of mutant synthase and a reduced yield (26-44%). Michaelis-Menten analyses with the partially purified enzyme revealed that each mutant synthase had a marked reduction in affinity for its coenzyme, pyridoxal 5'-phosphate, as well as reduced affinity and maximum velocity for both co-substrates, L-homocysteine and L-serine. Even at saturating concentrations of coenzyme, mutant synthase activity was less than 3% of control. Mutant synthase was also far more thermolabile than control enzyme. In the absence of added coenzyme, heating for 10 min at 55 degrees led to complete loss of mutant activity whereas control activity was reduced by 60%. Significantly, addition of saturating concentration of coenzyme prior to heating increased thermostability of both control and mutant synthase, the fractional increase being considerably greater in the mutants. We conclude that these patients suffer from a mutation of the synthase apoenzyme which impairs coenzyme binding, and that this primary abnormality results in reduced total enzyme activity in two ways: by reducing holoenzyme formation; and by accelerating apoenzyme degradation. We propose that pharmacologic amounts of pyridoxine increase holoenzyme formation modestly, thereby enhancing catalytic activity and slowing apoenzyme turnover.
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PMID:On the mechanism of pyridoxine responsive homocystinuria. II. Properties of normal and mutant cystathionine beta-synthase from cultured fibroblasts. 453 Oct 18

Cell-free extracts of Bacillus megaterium form beta-cyanoalanine (beta-CNA)-(14)C from Na(14)CN and l-cysteine, O-acetyl-l-serine or, to a lesser extent, l-serine. However, the presence of cyanide in the growth medium does not increase the capacity of cell extracts to catalyze the formation of beta-CNA from cysteine and cyanide. The formation of beta-CNA is readily detected in extracts of cells grown in synthetic media with sulfate or l-djenkolic acid as sulfur sources; such cells also exhibit an increased ability to form cysteine when compared with cells grown on cysteine as the sulfur source. beta-CNA formation could not be detected in extracts of cells grown on cysteine as the sulfur source. A 40-fold purification of the O-acetyl-serine sulfhydrylase resulted in the co-purification of the beta-CNA-forming activity. The sulfhydrylase and the beta-CNA-forming activity co-chromatographed on diethyl-aminoethyl cellulose and Sephadex G-100.
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PMID:Formation of -cyanoalanine by O-acetylserine sulfhydrylase. 500 Nov 94

The formic acid extracts of several glutathione-deficient strains of Escherichia coli have been assayed for the presence of the mixed disulfide of CoA and glutathione, CoASSG. Strains deficient in gamma-glutamyl-cysteine synthase (EC 6.3.2.2) produced only CoA dimer. Strains deficient in glutathione synthase (EC 6.3.2.3) produced the mixed disulfide of CoA and the gamma-glutamylcysteine dipeptide. The pool size of total CoA in the cell did not change significantly even in the absence of glutathione.
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PMID:Effect of glutathione deficiency on the pool of CoA-glutathione mixed disulfide in Escherichia coli. 611 90

We have purified three low-abundance hepatic mRNAs to near homogeneity by polysome immunoadsorption. The mRNAs coding for the precursor of ornithine transcarbamoylase [carbamoylphosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3], the precursor of the beta-subunit of propionyl-CoA carboxylase [propionyl-CoA:carbon dioxide ligase (ADP-forming), EC 6.4.1.3], and cystathionine beta-synthase [L-serine hydro-lyase (adding homocysteine), EC 4.2.1.22], representing approximately 0.20, 0.02, and 0.015% of total hepatic mRNA, respectively, were purified 450- to 6,300-fold. We used the following steps: interaction of rat liver polysomes with an IgG fraction of monospecific antisera raised against each polypeptide; immobilization of polysome-antibody complexes on a protein A-Sepharose column; removal of the bulk of polysomes by extensive washing; dissociation of ribosomal subunits and elution of specific mRNA with EDTA; and isolation of the eluted mRNA by chromatography on an oligo(dT)-cellulose column. It seems likely that this procedure will permit isolation of other low-abundance mRNAs and subsequent cloning of their respective cDNAs.
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PMID:Purification of low-abundance messenger RNAs from rat liver by polysome immunoadsorption. 618 Apr 33

The immunochemical reactivity of unfractionated antibodies elicited by denatured beta 2 subunits of Escherichia coli tryptophan synthase [L-serine hydro-lyase (adding indole) EC 4.2.1.20] with the homologous antigen and with the native enzyme is examined. These antibodies recognize the native apoenzyme nearly as well as the denatured protein. On the contrary, after binding of its cofactor, pyridoxal 5'-phosphate, the protein exhibits a much lower immunoreactivity toward these antibodies. This decrease of affinity becomes even more pronounced when the beta 2 protein interacts with the alpha subunit. Similarly, reduction of the Schiff base formed between the cofactor and the protein leads to a strong decrease of immunoreactivity. To account for these results, it is proposed that apo-beta 2 must be a dynamic flexible structure that easily exposes to the solvent regions of its polypeptide chain that normally are buried in its interior. The increase in rigidity of this structure upon binding of the cofactor, reduction of Schiff base, and formation of the alpha 2 beta 2 complex would then account for the decreased immunoreactivity of these various states of the native beta 2 protein.
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PMID:Immunochemical evidence for conformational flexibility and its modulation by specific ligands in the beta 2 subunit of Escherichia coli tryptophan synthase. 619 71

Control of coenzyme A (CoA) synthesis was studied in isolated perfused rat hearts. The data obtained support the hypothesis that phosphorylation of pantothenic acid by pantothenate kinase is the flux-generating reaction in the pathway of CoA synthesis. This reaction operated in the cell far removed from its thermodynamic equilibrium; it was saturated with substrates under all conditions studied; and the concentration of substrate changed in the opposite direction to flux when flux was altered. The reaction was subject to control by external factors associated with oxidation of glucose, pyruvate, or palmitate. CoA synthesis from 4'-phosphopantothenic acid was not inhibited by glucose and pyruvate, suggesting that pantothenate kinase is the only reaction in the pathway that is controlled in isolated hearts. Maximum rates of CoA synthesis in perfused hearts with pantothenate kinase stimulation were dependent on a supply of exogenous cysteine. Perfusate [14C]cysteine was incorporated into intermediates of this pathway and CoA. When protected from oxidation to cystine by low concentrations of dithiothreitol, 0.1 mM cysteine in the perfusate resulted in maximum rates of CoA synthesis. Evidence was obtained that indicates that addition of cysteine relieves a substrate limitation at the 4'-phosphopantothenyl cysteine synthase reaction.
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PMID:Pantothenate kinase and control of CoA synthesis in heart. 632 96

Mutants carrying defects in cysteine synthase A or B or both were isolated from Salmonella typhimurium LT2. Parent strains were able to grow on minimal media containing sulfate, sulfite, sulfide, or thiosulfate as sulfur sources. Mutants lacking cysteine synthase B were unable to grow on thiosulfate, whereas mutants lacking cysteine synthase A grew on the four inorganic sulfur sources described above with little difference in their growth rates. Mutants lacking both cysteine synthases failed to grow on media containing any of the inorganic sulfur sources tested. Purification of cysteine synthase B resulted in the copurification of S-sulfocysteine synthase. In addition, the two activities were also cotransduced. These activities appear to be associated with the cysM gene, and this is able to be cotransducted with the cysK gene at a high frequency. From these results, it may be concluded that thiosulfate is assimilated via S-sulfocysteine exclusively with the aid of S-sulfocysteine synthase.
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PMID:Evidence that thiosulfate assimilation by Salmonella typhimurium is catalyzed by cysteine synthase B. 635 63

S-Sulfocysteine synthase was isolated from Salmonella typhimurium LT-2 to homogeneous form with polyacrylamide gel electrophoresis. The molecular weight of this enzyme was determined to be ca. 55,000. The enzyme consisted of two identically sized subunits, and it contained one pyridoxal phosphate per subunit. The enzyme catalyzed the biosynthesis of cysteine or S-methylcysteine from sulfide or methanethiol and O-acetylserine, respectively, in addition to the formation of S-sulfocysteine from thiosulfate and O-acetylserine. The enzyme is identical to cysteine synthase B. The intracellular level of this enzyme was regulated by lesser extents of the same factors as those effective for cysteine synthase A.
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PMID:Enzymatic proof for the identity of the S-sulfocysteine synthase and cysteine synthase B of Salmonella typhimurium. 637 37

Several sul-reg mutants of Aspergillus nidulans isolated as constitutive for arylsulphatase were studied with respect to the regulation of enzymes involved in cysteine and homocysteine synthesis and to the pool of sulphur amino acids. All mutants examined showed a decreased concentration of glutathione as compared with the wild type, and all mutants, with one exception, had a decreased total pool of sulphur amino acids. The results suggest that the mutants are leaky in the sulphate assimilation pathway. They show derepression of cysteine synthase, homocysteine synthase, cystathionine beta-synthase and gamma-cystathionase. In spite of having derepressed homocysteine synthase, the enzyme which constitutes an alternative pathway for homocysteine synthesis, the sul-reg mutations do not suppress lesions in genes required for the main homocysteine-synthesizing pathway. This indicates that the derepression of homocysteine synthase is not in itself sufficient for physiological functioning of this enzyme, but seems to depend also on the effectiveness of cysteine synthesis and sulphide formation.
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PMID:Mutations affecting the sulphur assimilation pathway in Aspergillus nidulans: their effect on sulphur amino acid metabolism. 638 43


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