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At least 1,171 records · Page 65Linked to original sources
PubMed1997

Identification of Saccharomyces cerevisiae GLY1 as a threonine aldolase: a key enzyme in glycine biosynthesis.

Determination of enzyme-specific activities revealed that GLY1 encodes a threonine aldolase (TA) in Saccharomyces cerevisiae. A knock-out mutant auxotrophic for glycine lacked detectable activity. After transformation with YEp24GLY1 glycine prototrophy was restored and TA-specific activity was 16-fold higher than in the wild type. Growth experiments using glucose as the sole carbon source showed that GLY1 is more important for glycine biosynthesis than SHM1 and SHM2 encoding alternative serine hydroxymethyltransferases. On ethanol as carbon source simultaneous disruption of GLY1, SHM1 and SHM2 did not lead to glycine auxotrophy because glycine biosynthesis proceeds via alanine glyoxylate aminotransferase.

Alanine Transaminase↗
PubMed1998

Rapid accumulation of intracellular 2-keto-3-deoxy-6-phosphogluconate in an Entner-Doudoroff aldolase mutant results in bacteriostasis.

The accumulation of 2-keto-3-deoxy-6-phosphogluconate, the key intermediate of the Entner-Doudoroff pathway, has long been thought to inhibit growth of bacteria, but careful measurements of 2-keto-3-deoxy-6-phosphogluconate accumulation by growing cells and the correlation of intracellular 2-keto-3-deoxy-6-phosphogluconate levels to growth inhibition had not been made. A system designed for this purpose was developed in Escherichia coli strains, allowing 2-keto-3-deoxy-6-phosphogluconate accumulation to be experimentally induced and measured by extraction of the cell pool. Addition of gluconate to a strain which lacked 2-keto-3-deoxy-6-phosphogluconate aldolase and overproduced 6-phosphogluconate dehydratase resulted in an increase in the intracellular concentration of 2-keto-3-deoxy-6-phosphogluconate from undetectable levels to 2.0 mM within 15 s, as measured by anion-exchange HPLC. The accumulation of 2-keto-3-deoxy-6-phosphogluconate was correlated with an immediate and significant decrease in growth; this inhibition was determined to be bacteriostatic and not bactericidal. It had been proposed that the mechanism of 2-keto-3-deoxy-6-phosphogluconate toxicity involves competitive inhibition of 6-phosphogluconate dehydrogenase and the consequent block of the pentose phosphate pathway. An experiment addressing this hypothesis failed to provide any supporting data.

Aldehyde-Lyases↗
PubMed2000

trans-o-Hydroxybenzylidenepyruvate hydratase-aldolase as a biocatalyst.

The hydratase-aldolase-catalyzed conversion of trans-o-hydroxybenzylidenepyruvate to salicylaldehyde and pyruvate is an intermediate reaction in the conversion of naphthalene to salicylate by bacteria. Here, a variety of aromatic aldehydes and some nonaromatic aldehydes together with pyruvate have been shown to be substrates for aldol condensations catalyzed by this enzyme in extracts of the recombinant strain Escherichia coli JM109(pRE701). Some of the products of these reactions were also compared as substrates in the opposite (hydration-aldol cleavage) reaction.

Aldehydes↗
PubMed1975

Formation and cleavage of 2-keto-3-deoxygluconate by 2-keto-3-deoxygluconate aldolase of Aspergillus niger.

2-Keto-3-deoxygluconate aldolase of Aspergillus niger, an enzyme that has not been reported previously, was purified 468-fold. Maximal activity was obtained at pH 8.0 and 50 C. The enzyme exhibited relative stereochemical specificity with respect to glyceraldehyde. The Km values for 2-keto-3-deoxygluconate, glyceraldehyde, and pyruvate were 10, 13.3, and 3.0 mM, respectively. The effects of some compounds and inhibitors on enzyme activity were examined. Stability of the enzyme under different conditions was investigated. The equilibrium constant was about 0.33 X 10(-3) M.

Aldehyde-Lyases↗
PubMed1994

Organization and evolution of naphthalene catabolic pathways: sequence of the DNA encoding 2-hydroxychromene-2-carboxylate isomerase and trans-o-hydroxybenzylidenepyruvate hydratase-aldolase from the NAH7 plasmid.

The sequence of a 2,437-bp DNA segment from the naphthalene upper catabolic pathway operon of plasmid NAH7 was determined. This segment contains three large open reading frames designated nahQ', nahE, and nahD. The first of these is the 3' end of an open reading frame that has no known function, the second (993 bp) encodes trans-o-hydroxybenzylidenepyruvate hydratase-aldolase (deduced molecular weight, 36,640), and the third (609 bp) encodes 2-hydroxychromene-2-carboxylate isomerase (deduced molecular weight, 23,031). This DNA has a high degree of sequence homology (greater than 91% for the first 2161 bp) with a DNA segment from the dox (dibenzothiophene oxidation) operon of Pseudomonas sp. strain C18, which encodes a pathway analogous to that encoded by NAH7. However, 84 bp downstream from nahD, the last gene in the nah operon, this homology ends. This 84-bp sequence at the downstream end of nah and dox homology has 76% homology to a sequence that occurs just upstream of the nah promoter in NAH7. These directly repeated 84-bp sequences thus encompass the upper-pathway nah operon and constitute the ends of a highly conserved region.

Amino Acid Sequence↗
PubMed1997

L-allo-threonine aldolase from Aeromonas jandaei DK-39: gene cloning, nucleotide sequencing, and identification of the pyridoxal 5'-phosphate-binding lysine residue by site-directed mutagenesis.

We have isolated the gene encoding L-allo-threonine aldolase (L-allo-TA) from Aeromonas jandaei DK-39, a pyridoxal 5'-phosphate (PLP)-dependent enzyme that stereospecifically catalyzes the interconversion of L-allo-threonine and glycine. The gene contains an open reading frame consisting of 1,014 nucleotides corresponding to 338 amino acid residues. The protein molecular weight was estimated to be 36,294, which is in good agreement with the subunit molecular weight of the enzyme determined by polyacrylamide gel electrophoresis. The enzyme was overexpressed in recombinant Escherichia coli cells and purified to homogeneity by one hydrophobic column chromatography step. The predicted amino acid sequence showed no significant similarity to those of the currently known PLP-dependent enzymes but displayed 40 and 41% identity with those of the hypothetical GLY1 protein of Saccharomyces cerevisiae and the GLY1-like protein of Caenorhabditis elegans, respectively. Accordingly, L-allo-TA might represent a new type of PLP-dependent enzyme. To determine the PLP-binding site of the enzyme, all of the three conserved lysine residues of L-allo-TA were replaced by alanine by site-directed mutagenesis. The purified mutant enzymes, K51A and K224A, showed properties similar to those of the wild type, while the mutant enzyme K199A was catalytically inactive, with corresponding disappearance of the absorption maximum at 420 nm. Thus, Lys199 of L-allo-TA probably functions as an essential catalytic residue forming an internal Schiff base with PLP of the enzyme to catalyze the reversible aldol reaction.

Aeromonas↗
PubMed2005

Multiple regulators control expression of the Entner-Doudoroff aldolase (Eda) of Escherichia coli.

The Escherichia coli eda gene, which encodes the Entner-Doudoroff aldolase, is central to the catabolism of several sugar acids. Here, we show that Eda synthesis is induced by growth on gluconate, glucuronate, or methyl-beta-D-glucuronide; phosphate limitation; and carbon starvation. Transcription of eda initiates from three promoters, designated P1, P2, and P4, each of which is responsible for induction under different growth conditions. P1 controls eda induction on gluconate and is regulated by GntR. P2 controls eda induction on glucuronate and galacturonate and is regulated by KdgR. P4 is active under conditions of phosphate starvation and is directly controlled by PhoB. In addition, CsrA activates Eda synthesis, apparently by an indirect mechanism that may be involved in the modest changes in expression level that are associated with carbon starvation. The complex regulation of eda is discussed with respect to its several physiological roles, which apparently accommodate not only sugar acid catabolism but also detoxification of metabolites that could accumulate during starvation-induced stress.

Aldehyde-Lyases↗
PubMed2001

Cloning, sequencing, and expression of the gene encoding 4-hydroxy-4-methyl-2-oxoglutarate aldolase from Pseudomonas ochraceae NGJ1.

A DNA fragment that carried the gene (proA) encoding 4-hydroxy-4-methyl-2-oxoglutarate aldolase was cloned from the chromosomal DNA of Pseudomonas ochraceae NGJ1, and the coding region was assigned to the nucleotide sequence based on the N-terminal amino acid sequence of the enzyme purified from the organism. The proA gene was 684 bp long, corresponding to a protein of 227 amino acid residues with a calculated molecular mass of 24,067 Da. The genes encoding a putative transporter and a 4-oxalomesaconate hydratase were upstream, and a 3'-truncated gene encoding 2-pyrone-4,6-dicarboxylate lactonase was downstream from the proA gene in the same orientation on the DNA fragment. The proA gene product was overproduced in Escherichia coli and briefly purified to homogeneity from the crude extract by a two-step purification. The molecular and catalytic properties of the gene product were similar to those of the P. ochraceae enzyme.

Amino Acid Sequence↗
PubMed1975

The stereochemistry at carbon 3 of pyruvate lyase condensation products. 2-Keto-3-deoxygluconate-6-phosphate aldolase.

In a condensation between [3-3H3]pyruvate and D-glyceraldehyde-3-P as catalyzed by 2-keto-3-deoxygluconate-6-P aldolase (EC 4.1.2.14) of Pseudomonas putida, C--C synthesis occurred appreciably faster than C--3H bond breaking. Since tritium is present in tritiated pyruvate in tracer amounts, this result showed hydrogen isotope discrimination in pyruvate deprotonation and suggests enolpyruvate generation to be at least partially rate-limiting in the condensation reaction. Consequently, in a condensation reaction between [3-3H, 2H,H]pyruvate of known chirality and D-glyceraldehyde-3-P, the newly synthesized C--C bond would be enriched for at what was the C--H bond of chiral pyruvate, discriminating against the C--2H and C--3H bonds. Additional studies showed that condensations between (3S)-[3-3H, 2H,H]- or (3R)-[3-3H, 2H,H]pyruvate and D-glyceraldehyde-3-P yielded predominantly (3S)- or (3R)-2-keto-3-deoxy[3-3H, 2H]gluconate-6-P, respectively. By comparison with sterochemical models, it was concluded that condensation occurred with retention of configuration at C-3. Thus in the turnover of substrates as catalyzed by this enzyme, both the exchanging proton from water and D-glyceraldehyde-3-P attack the same face of the enzyme-bound pyruvyleneamine.

Aldehyde-Lyases↗
PubMed1977

Specificity of 2-keto-3-deoxygluconate-6-P aldolase for open chain form of 2-keto-3-deoxygluconate-6-P.

2-Keto-3-deoxygluconate-6-P exists as an euqilibrium of three forms at 25 degrees measurable by 13C NMR: alpha-furanose anomer (41%), beta-furanose anomer (50%), and open chain keto (9%). The three forms are interconverted rapidly (greater than 0.5 s-1) so that the unidirectional rates of furanose ring opening and closing can be quantitated by an NMR line broadening method. The 2-keto-3-deoxygluconate aldolase is specific for only one of these forms, the open chain keto form. The rates for ring opening calculated from the rapid kinetic enzyme system compare closely with those obtained with the NMR method.

Aldehyde-Lyases↗
PubMed1979

Interaction of the chiral pyruvate analog, 2-keto-3-bromobutyrate, with pyruvate lyases. 2-Keto-3-deoxygluconate-6-phosphate aldolase of Pseudomonas putida.

The enzyme 2-keto-3-deoxygluconate-6-P aldolase of Pseudomonas putida is inactivated by one of the chiral forms of 2-keto-(3RS)-3-bromobutyric acid (bromoketobutyrate). The inactivation shows saturation kinetics and competition with pyruvate. The minimal inactivation half-time is 4 min and that concentration of bromoketobutyrate half-saturating the enzyme is 2 mM. (3RS)-[3-3H]bromoketobutyrate is catalytically detritiated during enzyme inactivation. A kinetic analysis of rates gave data consistent with both catalysis and inactivation occurring at a single protein site, the catalytic site. The enzyme only detritiates one of the two optical isomers of bromoketobutyrate, and that form which is detritiated also alkylates the catalytic site. The inactive isomer of reagent degrades, with inversion, to L-lactate so that the chiral form specific for the enzyme is 2-keto-(3S)-3-bromobutyrate. Thus, as is the case with bromopyruvate, the enzyme catalyzes protonation of the re face at C-3 of the enzyme-reagent eneamine. As a result, bromoketobutyrate could serve as a chiral probe for stereochemical constraints of selected pyruvate-specific lyase active sites.

Aldehyde-Lyases↗
PubMed1984

Malyl-CoA formation in the NAD-, CoASH-, and alpha-ketoglutarate dehydrogenase-dependent oxidation of 2-keto-4-hydroxyglutarate. Possible coupled role of this reaction with 2-keto-4-hydroxyglutarate aldolase activity in a pyruvate-catalyzed cyclic oxidation of glyoxylate.

The alpha-ketoglutarate dehydrogenase complex of either pig heart or Escherichia coli catalyzes a NAD- and CoASH-dependent oxidation of 2-keto-4-hydroxyglutarate which is stereoselective toward the L-isomer of this hydroxyketo acid. L-Malyl-CoA is the product of the reaction; the evidence includes observing (a) a steady increase in absorbance at 230 nm during the oxidation of 2-keto-4-hydroxyglutarate, (b) a positive response of oxidation reaction mixtures to neutral hydroxylamine, (c) loss of the two foregoing results concomitant with release of thiol-reacting material and the formation of free malate when reaction mixtures are heated, (d) formation of a hydroxamate which has chromatographic mobilities identical to that of chemically synthesized malate hydroxamate, (e) enzymatic formation of a radioactive product from 14C-labeled 2-keto-4-hydroxyglutarate which co-migrates with chemically synthesized malyl-CoA, and (f) hydrolysis of the product by citrate synthase, an enzyme absolutely specific for citryl-CoA and L-malyl-CoA. A 1:1:1 stoichiometric relationship exists between the amount of 2-keto-4-hydroxyglutarate oxidized, NAD reduced, and malate (or malyl-CoA) formed. Results from studies in which either 14C-labeled 2-keto-4-hydroxyglutarate, pyruvate, or glyoxylate is incubated with mixtures of purified enzymes or extracts of E. coli support the suggestion that the aldolase which preferentially catalyzes formation of L-2-keto-4-hydroxyglutarate from pyruvate plus glyoxylate in E. coli is coupled with the oxidative decarboxylation of this substrate, as reported here, and other enzymes in a multistep pyruvate-catalyzed cyclic oxidation of glyoxylate.

Acyl Coenzyme A↗
PubMed1984

Induction of deoxyribose-5-phosphate aldolase of Bacillus cereus by deoxyribonucleosides.

In Bacillus cereus purine ribonucleosides and deoxyribonucleosides share a common inducible catabolic pathway, leading to the formation of ribose-5-P or deoxyribose-5-P respectively inside the cell, while the purine ring remains in the external medium. Both ribo- and deoxyribonucleosides are inducers of adenosine deaminase, inosine-guanosine phosphorylase and phosphopentomutase, the enzymes of the catabolic pathway. We now show that deoxyribonucleosides, but not ribonucleosides, induce the aldolase specific for deoxyribose-5-P (2-deoxy-D-ribose-5-phosphate acetaldehyde lyase, EC 4.1.2.4), thus allowing the sugar moiety of exogenous deoxyribonucleosides to be utilized as an energy source.

Aldehyde-Lyases↗