PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Aldehyde-Lyases”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1979

Kinetic properties of the purified 3-hexulosephosphate synthase from Pseudomonas oleovorans.

The kinetic characteristics of the purified 3-hexulosephosphate synthase from the facultative methylotroph Pseudomonas oleovorans were investigated. It could be demonstrated that the dependence of the reaction rate on the rib(ul)ose-5-phosphate as well as the formaldehyde concentration has a complex shape with the appearence of plateau and trough regions. The shape of the curve is changed in dependence on the fixed level of the second substrate. Multiple forms of the 3-hexulosephosphate synthase were found to be responsible for the generation of the complex kinetic characteristics. By means of ion exchange chromatography it was possible to separate four active enzyme forms with different kinetic characteristics. These forms were also found to be interconvertible. This behaviour of the 3-hexulosephosphate synthase is assumed to have the main regulatory function of the enzyme.

Aldehyde-Lyases↗
PubMed1976

Multiple regulation of nucleoside catabolizing enzymes: effects of a polar dra mutation on the deo enzymes.

Strains with an amber, polar mutation in the dra1 gene have been isolated. The mutation was introduced into a set of isogenic strains, wild type or with concurrent regulatory mutations, and further characterized by suppression and heat inactivation experiments. The effect of the polar dra mutation on the three remaining genes of the deo operon, the tpp, drm and pup genes, was determined by estimating the enzyme levels in the various dra-mutants. The effect was found to be non-coordinate, indicating the formation in the cells of two types of transcripts: A tetracistronic unit, containing the message from all four genes, and a dicistronic unit, covering the two distal genes only.

Aldehyde-Lyases↗
PubMed1978

Regulation of the deo operon in Escherichia coli: the double negative control of the deo operon by the cytR and deoR repressors in a DNA directed in vitro system.

The synthesis of the four enzymes of the deo operon in Escherichia coli is known from in vivo experiments to be subject to a double negative control, exerted by the products of the cytR and deoR genes. A DNA-directed in vitro protein synthesizing system makes the deo enzymes (exemplified by thymidine phosphorylase) in agreement with in vivo results. Enzyme synthesis is stimulated by cyclic AMP and repressed by the cytR and deoR gene products. Repression by the cytR repressor is reversed by cytidine or adenosine in the presence of cyclic AMP, while repression by the deoR repressor is reversed by deoxyribose-5-phosphate. Assays for the presence of the cytR and deoR repressors were established by use of S-30 extracts prepared from the regulatory mutants. Dissociation constants for repressor-operator binding as well as for repressor-inducer interactions have been estimated from the results.

Aldehyde-Lyases↗
PubMed1975

Aromatic amino acid biosynthesis in Alcaligenes eutrophus H16. I. Properties and regulation of 3-deoxy-d-arabino heptulosonate 7-phosphate synthase.

Properties and regulation of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHP-synthase), EC4.1.2.15, from Alcaligenes eutrophus H16 were investigated. DAHP synthase was unstable during manipulations such as dialysis, dilution, ammonium sulfate fractionation, chromatography on DEAE-cellulose or Sephadex G-200. For kinetic measurements Sephadex G-25 treated crude extracts were used. The enzyme was not affected by thiol reagents, EDTA or divalent metal ions. The activation energy, deltaH, amounted to 16100 cal/mole. Between pH 7.2 and pH 8.2 there was little change of enzyme activity. The Km-values for the two substrates were found to be 0.043 mM phosphoenolpyruvate and 0.055 mM erythrose-4-phosphate. DAHP-synthase was inhibited by 0.5 mM phenylalanine for 60% and by 0.5 mM tyrosine for 20%. In the presence of both amino acids cumulative inhibition occurred amounting to about 70%. No other amino acid exerted inhibitory effects. A repression of DAHP-synthase by the aromatic amino acids was not observed. Some other strains of hydrogen bacteria were included in this study. The DAHP synthase from strain 12/60/X and Corynebacterium autotrophicum 7C was unregulated. The enzyme from strain 33/X was subject to retro-tyrosine inhibition and from strain 3/2, H1 and H20 were subject to cumulative inhibition.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed1975

Regulated in vitro synthesis of the enzymes of the deo operon of Escerichia coli. properties of the DNA directed system.

The four enzymes deoxyriboaldolase, thymidine phosporylase, deoxyribomutase, and purine nucleoside phosphorylase have been synthesized in substantial amounts in a DNA-dependent in vitro system programmed with DNA containing the deo operon. The synthesis is greatly stimulated by deoxyribose-5-phosphate and cyclic AMP indicating that the deoR repressor and the catabolite activating protein (CAP) are highly active under our cell-free conditions. In contrast it has not yet been possible to observe a reproducible effect of the cytR repressor in vitro. The sequential appearance of active enzymes has confirmed the direction of transcription as being dra-tpp-drm-pup and has indicated that the four genes are transcribed into a single tetracistronic message.

Aldehyde-Lyases↗
PubMed1976

Purification and properties of tyrosine-sensitive 3-deoxy-D-arabino-heptolosonate-7-phosphate synthetase of Escherichia coli K12.

1. The tyrosine-sensitive allosteric first enzyme of the aromatic amino acid biosynthetic pathway, 3-deoxy-D-arabinoheptulosonate 7-phosphate synthetase (7-Phospho-2-keto-3-deoxy-D-arabino-heptonate D-erythrose 4-phosphate-lyase (pyruvate phosphorylating), EC 4.1.2.15) has been purified from a mutant strain of Escherichia coli. 2. The enzyme activity was inhibited to 50% at 2-10(-5) M tyrosine and to 90% at 2-10(-4) M tyrosine concentration. At tyrosine concentrations lower than 2-10(-5) M a cooperative interaction between tyrosine binding sites was observed. 3. Co2+ increased the enzyme activity about 2-2.5-fold. The presence of Co2+ ions stabilized the enzyme. EDTA inhibited the enzyme activity, and this inhibition was reversed by Co2+. Tyrosine-sensitive DAHP synthetase seems to be a metal containing enzyme. 4. Kinetic experiments were carried out to study the catalytic action. Contrary to earlier suggestions it is concluded, that the reaction mechanism appears to be more complex--with either the ping-pong or sequential type predominating, depending on conditions.

Aldehyde-Lyases↗
PubMed1977

Magnitude of the equilibrium isotope effect on carbon-tritium bond synthesis.

The exchange of tritium from 3HOH into the methyl group of pyruvate catalyzed by 6-phospho-2-keto-3-deoxygluconate aldolase (6-phospho-2-keto-3-deoxy-D-gluconate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.14) of Pseudomonas putida shows an equilibrium isotope effect of 0.78. From this value and the deuterium effect on the fumarase equilibrium (Thomson, J.F. (1960) Arch. Biochem. Biophys. 90, 1), one can calculate by use of the relative fractionation factors of Hartshorn and Shiner (Hartshorn, S.R. and Shiner, Jr., V.J. (1972) J. Am. Chem. Soc. 94, 9002), fractionation factors for transfer of deuterium or tritium from water to a number of organic molecules of interest.

Aldehyde-Lyases↗
PubMed1977

Sulfhydryl groups in relation to the structure and catalytic activity of 2-oxo-4-hydroxyglutarate aldolase from bovine liver.

Bovine liver 2-oxo-4-hydroxyglutarate aldolase (suggested name: 2-oxo-4-hydroxyglutarate glyoxylate-lyase catalyzing the reaction: 2-oxo-4-hydroxyglutarate in equilibrium pyruvate + glyoxylate) contains eight to ten sulfhydryl groups as determined by titration of the enzyme with either 5,5'-dithiobis(2-nitrobenzoic acid) (Nbs2) or p-mercuribenzoate in the presence of 1% sodium dodecyl sulfate. In the absence of a denaturant, all of the cysteinyl residues react with p-mercuribenzoate whereas only four are accessible to titration with Nbs2. No differences in -SH group reactivity can be detected during titration of the aldolase with p-mercuribenzoate. In contrast, two classes of sulfhydryls can be differentiated in the disulfide exchange reaction with Nbs2 in the absence of a denaturant; one -SH group (Class I) reacts rapidly whereas three additional thiols (Class II) titrate at approx. 0.1 the rate of the Class I-SH residue. Both pyruvate and glyoxylate protect one of the three -SH residues in Class II from reaction with Nbs2. Either substrate also prevents titration of one to two thiol groups by p-mercuribenzoate and decreases the rate of reaction of aldolase -SH groups with Nbs2 in 8 M urea. These ligand-induced changes in -SH reactivity provide a sensitive indication that the enzyme exists in an altered conformational state in the presence of either of its cosubstrates. Titration of the enzyme with either Nbs2 or p-mercuribenzoate results in a progressive loss of aldolase activity which is not proportional to the number of -SH groups modified. The enzyme retains 50% of the activity of the native enzyme when Class I and Class II thiols (i.e. four -SH groups total) are modified with Nbs2; 15% residual activity is still observed following titration of all of the cysteinyl residues with p-mercuribenzoate. Pyruvate and glyoxylate provide partial protection against inactivation. It is concluded that inactivation of 2-oxo-4-hydroxyglutarate aldolase by Nbs2 or p-mercuribenzoate is a consequence of alterations in protein structure which accompany modification of -SH groups. The data argue against the direct participation of an active-site thiol group in the catalytic mechanism of 2-oxo-4-hydroxyglutarate aldolase, be that aldol cleavage and condensation or beta-decarboxylation.

Aldehyde-Lyases↗
PubMed1978

3-Hexulosephosphate synthase from Methylomonas aminofaciens 77a. Purification, properties and kinetics.

3-Hexulosephosphate synthase (D-arabino-3-hexulose 6-phosphate formaldehyde lyase) was purified from an obligate methylotroph, Methylomonas aminofaciens, to homogeneity as judged by polyacrylamide gel electrophoresis and analytical ultracentrifugation. The molecular weight was determined to be 45 000-47 000 by sedimentation velocity and gel filtration. The enzyme appears to be composed of two identical subunits (Mr = 23 000). A bivalent cation is required for the activation and stabilization of the enzyme. The enzyme is specific for formaldehyde and D-ribulose 5-phosphate. The optimum pH is 8.0 (isoelectric point, pH 5.1) and the optimum temperature is 45 degrees C. Initial velocity studies are consistent with a sequential mechanism. The Michaelis constants are 0.29 mM for formaldehyde and 0.059 mM for D-ribulose 5-phosphate.

Aldehyde-Lyases↗
PubMed1976

A nonspecific inhibitory effect of tRNA on the activity of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from Saccharomyces cerevisiae.

The inhibitory effect of tRNA on yeast 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase (EC 4.1.2.15) has been reinvestigated. From earlier studies the inhibition by tRNAPhe appeared to be quite specific. This study shows that tRNAPhe is indeed a potent inhibitor but so is unfractionated tRNA, as well as ribosomal RNA and heparin. Complete digestion to mononucleotides relieves the inhibition. Since the enzyme requires a metal ion (Co2+) we suggest that the RNA and heparin are inhibitory by virtue of their capacity to chelate the Co2+.

3-Deoxy-7-Phosphoheptulonate Synthase↗