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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 enzymes necessary for the metabolism of methionine by the trans-sulfuration pathway, methionine adenosyltransferase (EC 2.5.1.6), adenosylhomocysteinase (EC 3.3.1.1), cystathionine beta-synthase (EC 4.2.1.22) and cystathionine gamma-lyase (EC 4.4.1.1) were identified in Tetrahymean pyriformis. The ability of these cells to transfer 35S from E135S]methionine to form [35S] cysteine was also observed and taken as direct evidence for the functional existence of this pathway in Tetrahymena. An intermediate in the pathway and an active methyl donor, S-adenosylmethionine, was qualitatively identified in Tetrahymena and its concentration was found to be greater in late stationary phase cells than in early stationary phase cells.
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PMID:The transsulfuration pathway in Tetrahymena pyriformis. 1 63

Genetic exchange between the structural genes for the alpha chain of tryptophan synthetase [tryptophan synthase; L-serine hydro-lyase (adding indoleglycerol-phosphate), EC 4.2.1.20] of E. coli and S. typhimurium yielded recombinant genes that specified functional hybrid polypeptides. The alpha chains produced by three recombinants appeared to be identical but differed from those of E. coli and S. typhimurium by at least 27 and 8 amino acid residues, respectively. In vivo and in vitro tests of enzyme function suggest that the hybrid alpha chains are near-equivalent to their fully active parental proteins.
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PMID:Structure and properties of a hybrid tryptophan synthetase of alpha chain produced by genetic exchange between Escherichia coli and Salmonella typhimurium. 6 83

Serine dehydratase (L-serine hydro-lyase, EC 4.2.1.13) WAS DEMONSTRATED IN LIVER TISSUE OF RATS BY AN INdirect immunofluorescent method. In the adult rat liver, serine dehydratase was localized to periportal hepatocytes, diffusely in their cytoplasm. The enzyme-specific fluorescence was absent or extremely low in the centrolobular hepatocytes. It was not demonstrated in nonparenchymal cells. Feeding a 90% protein diet for 5 days caused marked induction of this enzyme in the periportal and midzonal hepatocytes but no induction in the centrolobular hepatocytes. In the newborn rat liver, there was no apparent intralobular heterogeneity seen in the distribution of serine dehydratase, either before or after dietary induction. After 1 week of age, there was a gradual development of the intralobular hetero-geneity of the enzyme, which was emphasized by dietary stimulation. A comparative study of the induction pattern between the livers of intact and adrenalectomized rats suggested that there is no heterogeneity among serine-dehydratase-positive cells with respect to hormonal regulation of this enzyme by either glucagon or cortisone.
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PMID:Immunohistochemical demonstration of serine dehydratase in rat liver. 16 93

ATP-sulfurylase, cysteine synthase, homocysteine synthase, arylsulfatase and beta-cystathionase in Saccharomycopsis lipolytica are repressed on the addition of methionine, homocysteine or cysteine to the growth medium. The use of appropriate mutants enabled us to demonstrate that the synthesis of these enzymes is regulated by the system involving at least two low-molecular weight effectors--most likely cysteine and methionine (or their close derivatives).
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PMID:Regulation of s-amino acids biosynthesis in Saccharomycopsis lipolytica. 28 1

Globular proteins often appear to consist of distinct compact "domains," and the assumption is frequently implicitly made that these domains correspond to intermediate structures in the folding process. If this assumption is correct, the polypeptide fragment that builds up a domain should be able to spontaneously fold into its native conformation even when isolated. In an attempt to isolate and study such a fragment, the beta2 subunit of tryptophan synthetase [tryptophan synthase, L-serine hydro-lyase (adding indoleglycerol-phosphate), EC 4.2.1.20] has been subjected to controlled proteolysis. The resulting protein is shown to be a dimer, the protomer of which contains two nonoverlapping polypeptide chains of molecular weights 12,000 and 29,000. Though inactive, the nicked protein is shown to be in a conformation that closely resembles that of the original enzyme, since it still can form an enzyme-bound intermediate of the catalytic reactions. The fluorescence of this intermediate is used to characterize the binding sites for the cofactor (pyridoxal-P) and substrates, which are shown to exist on the nicked protein. The possibility is discussed of using the fragments isolated from the nicked protein to study individual steps of the enzymatic reaction, intracistronic complementation, and the folding process in the normal beta2 subunit.
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PMID:Preparation and characterization of a modified form of beta2 subunit of Escherichia coli tryptophan synthetase suitable for investigating protein folding. 32 25

Tryptophan synthase from Escherichia coli (L-serine hydro-lyase (adding indole), EC 4.2.1.20) synthesizes L-trypotophan from indoleglycerol phosphate and L-serine, releasing glyceraldehyde 3-phosphate, or from indole and L-serine. The latter reaction (B reaction), catalyzed either by the beta2 species or by the (alpha2 beta2) complex, has been studied by steady-state methods. A sequential mechanism is indicated. Inhibition experiments with the substrate analogue benzimidazole were carried out in order to distinguish between random and ordered mechanisms. The results are compatible with a random sequential mechanism. The dissociation constants of the enzyme-substrate complexes are evaluated. When catalyzed by the tetrameric complex (alpha2 beta2) the B reaction is inhibited by higher concentrations of the substrate indole. This inhibition does not follow the usual substrate inhibition pattern. The question whether the binding of indole to the alpha-subunit exerts an inhibitory effect on the beta2 species, possibly by reversing the activation by the alpha subunit of the beta2 species, is discussed.
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PMID:On the mechanism of action of Escherichia coli tryptophan synthase. Steady-state investigations. 34 87

Association of the apo-beta 2 and the holo-(beta-PLP)2 subunits of tryptophan synthase from Escherichia coli (L-serine hydro-lyase (adding indole) (EC 4.2.1.20)) with alpha subunits of the same enzyme has been studied by microcalorimetry. The results obtained from thermometric titrations clearly demonstrate that only the native complex alpha2beta 2 is formed, independent of an excess of alpha protein. The reaction of the holo-(beta-PLP)2 with alpha subunits at 25 degrees C is accompanied by a negative enthalpy change, which is almost twice as large as that for complex formation with the apo-beta 2 protein, thus indicating that the interaction enthalpy becomes more favorable in the presence of the coenzyme pyridoxal 5'-phosphate (PLP). Both reaction enthalpies show very large negative temperature coefficients, -3600 +/- 100 cal K-1 (Mol of beta 2)-1 being the value for the formation of the apoenzyme and -2300 +/- 100 cal K-1 (mol of beta 2)-1 pertaining to formation of the holoenzyme. The studies on the association of alpha and beta2 subunits in the two buffers revealed that at 25 degrees C approximately 0.75 proton are absorbed in the presence and absence of the coenzyme, whereas at 35 degrees C one proton is taken up from the solution when PLP is present, but two if the apo-beta 2 complex reacts. These results are a clear indication of energetic linkage between intersubunit interaction, hydrogen ion equilibria, and the binding of the coenzyme.
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PMID:Subunit interaction in tryptophan synthase of Escherichia coli: calorimetric studies on association of alpha and beta 2 subunits. 37 96

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).
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PMID:[Steady-state kinetics of reactions catalyzed by serine sulfhydrases of Saccharomyces serevisiae]. 38 Jun 61

1. Cystathionine beta-synthase activity isolated from fibroblast cultures obtained from the skin of a normal and a homocystinuric individual were both cross-reactive with normal human liver cystathionine beta-synthase antibody. 2. Isoelectric focusing revealed a substantial difference in the isoelectric points of the normal and abnormal fibroblast enzymes. 3. Treatment of purified samples of normal and abnormal fibroblast enzymes with sodium dodecylsulphate followed by polyacrylamide gel electrophoresis indicated that both normal and abnormal enzymes were composed of two sub-units of molecular weights 53000 and 70000. 4. A combination of urea and sodium dodecylsulphate treatment revealed that the respective 53000 molecular weight sub-units were different. 5. It has been concluded that the molecular defect in the case of pyridoxine non-responsive homocystinuria examined in the present investigation arises as a result of an alteration in the structural gene which codes for the lower molecular weight sub-unit of cystathionine beta-synthase.
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PMID:The molecular defect in a case of (cystathionine beta-synthase)-deficient homocystinuria. 40 47

Characteristics of a mutant of Cephalosporium acremonium with enhanced potential to utilize sulfate for cephalosporin C production were investigated with sulfur-starved cells. DL-Norleucine showed an inhibitory effect on cephalosporin C and penicillin N production by the mutant in the presence of a sulfur source such as sulfate, sulfite, thiosulfate, and L-cystine, but it exhibited no effect when it was added after a certain period of incubation. On the contrary, antibiotic production by the parent was stimulated by norleucine regardless of the addition time. An increase in the intracellular cysteine pool was found when the cells were incubated with L-methionine or norleucine and sulfate. Enzymatic studies revealed that methionine and norleucine stimulated the cysteine desulfhydrase formation, and this effect was significant in the mutant. Finally the mutant was found to have an enhanced L-serine sulfhydrylase activity. The increase in this enzyme activity in the mutant seems responsible for the increase in the sulfate-utilizing ability and the methionine sensitivity by maintaining a high level of the cysteine pool. Accordingly, the effect of methionine and norleucine is assumed to be exerted through cysteine.
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PMID:Sulfur metabolism of a mutant of Cephalosporium acremonium with enhanced potential to utilize sulfate for cephalosporin C production. 55 69


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