Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ISOMERASES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 559 records · Page 31Linked to original sources
PubMed1998

Structural analysis of N-linked carbohydrate chains of funnel web spider (Agelenopsis aperta) venom peptide isomerase.

The structure of the N-linked carbohydrate chains of peptide isomerase from the venom of the funnel web spider (Agelenopsis aperta) has been analyzed. Carbohydrates were released from peptide isomerase by hydrazinolysis and reductively aminated with 2-aminopyridine. The fluorescent derivatives were purified by phenol/chloroform extraction, followed by size-exclusion HPLC. The structure of the purified pyridylamino (PA-) carbohydrate chains were analyzed by a combination of two-dimensional HPLC mapping, sugar composition analysis, sequential exoglycosidase digestions, and mass spectrometry. The peptide isomerase contains six kinds of N-linked carbohydrate chains of truncated high-mannose type, with a fucose alpha 1-6 linked to the reducing N-acetylglucosamine in approximately 80% of them.

Amino Acid Isomerases↗
PubMed2000

Molecular analysis of maleate cis-trans isomerase from thermophilic bacteria.

Several strains of thermophilic bacteria containing maleate cis-trans isomerase were isolated from soil samples and identified as Bacillus stearothermophilus, Bacillus circulans, Bacillus brevis, and Deleya halophila. The maleate cis-trans isomerase was purified and characterized from one of the isolated strains, B. stearothermophilus MI-102. The purified enzyme of strain MI-102 showed higher thermal stability than the enzyme of a mesophile, Alcaligenes faecalis IFO13111. The seven maleate cis-trans isomerase genes (maiA) of thermophile were cloned and sequenced. B. stearothemophilus MI-102 MaiA has 67% amino acid identity with A. faecalis MaiA. All eight amino acid sequences of maiA gene products had significant conserved regions containing cysteine residues, which were previously suggested to be involved in an active site of the enzyme. To probe the catalytic mechanism, three cysteine residues in the conserved regions of A. faecalis MaiA were replaced with serine by site-directed mutagenesis. The results suggest that Cys80 and Cys198 play important roles in the enzyme activity.

Alcaligenes↗
PubMed1980

Mild purification procedure and subunit structure of glucosephosphate isomerase from baker's yeast.

A mild procedure for the purification of glucosephosphate isomerase from baker's yeast (Saccharomyces cerevisiae) is reported. The purified enzyme was homogeneous and did not contain charge isomers as shown by polyacrylamide gel electrophoresis as well as DEAE-Sepharose column chromatography. Its molecular weight determined by gel filtration and sucrose density gradient centrifugation was approximately 120 000, which agreed with that of the enzyme in the crude extract as well as that of the renatured enzyme. Gel filtration in 6M guanidine/HCl as well as acrylamide gel electrophoresis of sodium dodecyl sulfate denatured glucosephosphate isomerase showed one single peak and gave a subunit molecular weight of 60 000. Cross-linking patterns obtained with yeast glucosephosphate isomerase after treatment with dimethyl suberimidate resulted in the appearance of dimers as the largest-linked product of the enzyme subunit. After dissociation the enzyme can readily be reassociated and renatured with a yield of maximum 73% and a pseudo first order rate constant of 0.12 min-1 at 25 degrees C.

Chemical Phenomena↗
PubMed2005

Direct comparison of the crystal and solution structure of glucose/xylose isomerase from Streptomyces rubiginosus.

Glucose isomerase (D-xylose ketol-isomerase, EC 5.3.1.5.) catalyses the isomerization reaction of glucose and xylose. The small angle X-ray scattering (SAXS) data of glucose/xylose isomerase from Streptomyces rubiginosus were recorded for protein solution using synchrotron radiation. The experimental data were compared with theoretical scattering calculated on the basis of the known crystal structure (PDB code: 1OAD). The radius of gyration measured by SAXS (R(G)=3.30 nm) was almost identical and the maximum dimension in the distance distribution function was by about 2.5 % lower than the corresponding values calculated on the basis of the crystal structure.

Aldose-Ketose Isomerases↗
PubMed2004

Prolyl isomerases in yeast.

Prolyl isomerases are enzymes that catalyze cis-trans isomerization of peptidyl-prolyl bonds and span three structurally unrelated protein families: the cyclophilins, FKBPs, and parvulins. The genome of the budding yeast Saccharomyces cerevisiae encodes eight different cyclophilins (Cpr1 to Cpr8), four FKBPs (Fpr1 to Fpr4), and a single parvulin (Ess1). Remarkably, two of these proteins, cyclophilin A and FKBP12, are conserved from yeast to humans and mediate virtually all of the intracellular actions of the immunosuppressive antifungal drugs cyclosporin A, FK506, and rapamycin. The study of prolyl isomerases in S. cerevisiae has proven invaluable to understand the elusive functions of these proteins, and continues to provide new insights into their diverse cellular roles. Here we review the current state of knowledge about prolyl-isomerases in this model organism.

Conserved Sequence↗
PubMed2001

Isolation and characterization of a xylose-glucose isomerase from a new strain Streptomyces thermovulgaris 127, var. 7-86.

A thermostable D-xylose-glucose isomerase was isolated from the thermophilic strain Streptomyces thermovulgaris 127, var. 7-86, as a result of mutagenic treatment by gamma-irradiation of the parent strain, by precipitation and sequential chromatographies on DEAE-Sephadex A50, TSK-gel, FPLC-Mono Q/HR, and Superose 12 columns. The N-terminal amino acid sequence and amino acid analysis shows 73-92% homology with xylose-glucose isomerases from other sources. The native molecular mass, determined by gel filtration on a Superose 12 column, is 180 kDa, and 44.6 and 45 kDa were calculated, based on amino acid analysis and 10% SDS-PAGE, respectively. Both, the activity and stability of the enzyme were investigated toward pH, temperature, and denaturation with guanidine hydrochloride. The enzyme activity showed a clear pH optimum between pH 7.2 and 9.0 with D-glucose and 7.4 and 8.3 with D-xylose as substrates, respectively. The enzyme is active up to 60-85 degrees C at pH 7.0, using D-glucose, and up to 50-60 degrees C at pH 7.6, using D-xylose as substrates. The activation energy (Ea = 46 kJ x mol(-1)) and the critical temperature (Tc = 60 degrees C) were determined by fluorescence spectroscopy. Tc is in close coincidence with the melting temperature of denaturation (Tm = 59 degrees C), determined by circular dichroism (CD) spectroscopy. The free energy of stabilization in water after denaturation with Gdn.HCl was calculated to be 12 k x mol(-1). The specific activity (km values) for D-xylose-glucose isomerase at 70 degrees C toward different substrates, D-xylose, D-glucose, and D-ribose, were determined to be 4.4, 55.5, and 13.3 mM, respectively.

Aldose-Ketose Isomerases↗
PubMed1999

[Expression of xylose isomerase gene(xylA) in Saccharomyces cerevisiae from Clostridium thermohydrosulfuricum].

The Clostridium thermohydrosulfuricum xylA gene encoding xylose(glucose) isomerase was cloned in the yeast expression vector pMA91 under the control of the PGK promoter, resulting in pBX-1, and transformed into Saccharomyces cerevisiae. Production of recombinant xylose isomerase was seen in the a Coomassie stained SDS-PAGE gel and the molecular mass was estimated to be 43 kD. The recombinant xylose isomerase showed the highest activity at 85 degrees C and pH7. The specific activity under these condition was 1.0 U/mg protein. At 30 degrees C and 40 degrees C, the relative activity was reduced to 3.7% and 11%, respectively, of the maximum.

Aldose-Ketose Isomerases↗
PubMed1991

Xylose (glucose) isomerase gene from the thermophile Clostridium thermohydrosulfuricum; cloning, sequencing, and expression in Escherichia coli.

The xylose isomerase gene from the thermophile Clostridium thermohydrosulfuricum has been cloned, using a fragment of the Bacillus subtilis gene as a probe. The complete nucleotide sequence of the gene was analyzed. C. thermohydrosulfuricum is the most thermophilic organism from which a xylose isomerase gene has been cloned and characterized. Comparison with amino acid sequences from other xylose isomerases showed that amino acids involved in substrate binding and isomerization are well conserved. Purification of the enzyme produced in E. coli was done by heating a cell-free extract at 85 degrees C for 10 min, giving a 20-fold purified enzyme. The native enzyme is a homomeric tetramer with a molecular weight of 200,000.

Aldose-Ketose Isomerases↗
PubMedDate not supplied

Structural elements responsible for transglutaminase activity of protein disulphide isomerases and thioredoxins.

According to recent results both protein disulphide isomerase (PDI) and thioredoxin (Trx) enzymes have transglutaminase activity which can be linked to the thioredoxin box found in these proteins. Analysis of known protein disulphide isomerase and thioredoxin sequences has revealed the presence of conserved Cys, His and Asp residues required for transglutaminases to catalyze the incorporation of primary amines into protein-bound glutamine residues. The available 3D structures of PDIs and Trxs show that these residues are in close proximity to achieve transglutamylation of substrate proteins. The shared activities of the members of the large protein disulphide isomerase, thioredoxin and transglutaminase enzyme families reviewed here may have general biological significance in the regulation of cellular and tissue processes.

Amino Acid Sequence↗
PubMed1990

4-alkyl-o-quinone/2-hydroxy-p-quinone methide isomerase from the larval hemolymph of Sarcophaga bullata. I. Purification and characterization of enzyme-catalyzed reaction.

An enzyme which catalyzes the conversion of certain 4-alkyl-o-benzoquinones to 2-hydroxy-p-quinone methides has been purified to apparent homogeneity from the hemolymph of Sarcophaga bullata by employing conventional protein purification techniques. The purified enzyme migrated with an approximate molecular weight of 98,000 on gel filtration chromatography. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it migrated as a single band with a molecular weight of 46,000, indicating that it is made up of two identical subunits. It exhibited a pH optimum of 6.0 and readily converted chemically synthesized as well as enzymatically generated quinones derived from N-acetyldopamine, N-beta-alanyldopamine, and 3,4-dihydroxyphenethyl alcohol to highly unstable 2-hydroxy-p-quinone methides. The quinone methides thus formed were rapidly and nonenzymatically hydrated to form side chain hydroxylated o-diphenols as the stable product. In support of this proposition, when the enzyme reaction with N-acetyldopamine quinone was conducted in the presence of 10% methanol, racemic beta-methoxy-N-acetyldopamine was recovered as an additional product. The quinones of N-acetylnorepinephrine, N-beta-alanylnorepinephrine, and 3,4-dihydroxyphenylglycol were also attacked by the isomerase, resulting in the formation of N-acetylarterenone, N-beta-alanylarterenone and 2-hydroxy-3',4'-dihydroxyacetophenone, respectively as the stable products. The isomerase converted the dihydrocaffeiyl methyl amide quinone to its quinone methide analog which rapidly tautomerized to yield caffeiyl methyl amide. The importance of quinone isomerase in insect immunity and sclerotization of insect cuticle is discussed.

Animals↗
PubMed1986

Induction of L-arabinose isomerase in gamma-irradiated Escherichia coli.

Gamma irradiation of Escherichia coli B/r caused a dose-dependent inhibition of the capacity of the cells to synthesize L-arabinose isomerase in response to the inducer. At higher doses (18 krad and above), postirradiation incubation led to further inhibition of the capacity to synthesize L-arabinose isomerase, whereas cells receiving lower doses recovered from the damage to the enzyme synthesizing system following incubation. Cyclic AMP partially reversed the inhibitory effect on L-arabinose isomerase induction produced immediately after irradiation by all gamma-ray doses (up to 30 krad), but the enhanced inhibitory effect caused by induction in cells irradiated at higher doses could not be reversed by the nucleotide. It is suggested that although catabolite repression is partly responsible for causing the inhibition of the enzyme synthesizing capacity of the cells observed immediately after gamma irradiation, the enhanced inhibition caused by incubating cells irradiated at higher doses is not due to interference with the control mechanism regulated by catabolite repression.

Aldose-Ketose Isomerases↗
PubMed1988

Purification and characterization of chalcone isomerase from soybeans.

Chalcone isomerase from soybean has been purified 11,000-fold over the crude extract. The purification procedure features pseudo-affinity chromatography on an Amicon Matrex Orange A column with selective elution by a product of the enzymatic reaction. The purified enzyme is greater than 99.5% pure and possesses a specificity activity of 340 IU/mg, which is 520-fold greater than previously reported. The apparent molecular weight of the chalcone isomerase is 24,000 as determined from sodium dodecyl sulfate-polyacrylamide gels and from size exclusion chromatography under native conditions on Sephacryl S-200. The enzyme exists as a monomer that migrates on isoelectric focusing gels with a pI of 5.7. Amino acid analysis indicates that almost 50% of the residues are hydrophobic and yields a partial specific volume of 0.750 ml/g. Chalcone isomerase contains no carbohydrate moieties and has a blocked N terminus. The purified enzyme catalyzes the conversion of 2', 4',4-trihydroxychalcone (I) to (2S)-4',7-dihydroxyflavanone (II) at pH 7.6 with a second order rate constant, kcat/Km, of 1.1 X 10(9) M-1 min-1 and an apparent equilibrium constant, [II]/[I], of 7.6. The rate constant for the conversion of enzyme-bound substrate to the (2S)-flavanone, kcat = 11,000 min-1, exceeds the spontaneous conversion by 36 million-fold. The enzyme catalyzes the formation of (2S)-flavanone over 100,000-fold faster than to the (2R)-flavanone, indicating that the enzyme is highly stereoselective, yielding over 99.999% of the (2S)-flavanone.

Amino Acids↗
PubMedDate not supplied

[Effect of metal ions on the glucose isomerase activity of Streptomyces robeus S-606].

The intracellular glucose isomerase produced by Str. robeus S-606 refers to the group of isomerases activated most effectively by Mg2+. Besides, an activating effect of Fe3+, Co2+ and Mn2+ is observed. The optimal Mg2+ concentration for the D-glucose isomerization to D-fructose is 10(-2) M, and that of Co2+ is 100 times as low. Addition of Ca2+ (above 10% of the Mg2+ content) to the reaction mixture with the optimal Mg concentration inhibits the enzyme. At the same time Co2+ increases thermostability of glucose isomerase to a greater extent than Mg2+.

Aldose-Ketose Isomerases↗
PubMedDate not supplied

[Androgen regulation of aldolase and phosphohexose isomerase in the liver and seminal vesicles of white rats].

Testosterone at doses of 0.1 mg/kg and 1 mg/kg was shown to affect the phosphohexose isomerase and aldolase activities as well as the ratio of individual isozymes of aldolase. Phosphohexose isomerase from liver tissue was especially sensitive towards the effect of the hormone. The activity of phosphohexose isomerase was selectively inhibited by testosterone. Activity of aldolase from seminal vesicles was practically unaltered. Four fractions of aldolase were found in rat liver tissue, two fractions--in seminal vesicles. Testosterone at a dose of 1 mg/kg inhibited the aldolase of the B type in liver tissue. The activity of aldolase of type A was inhibited only after a single hormone administration.

Animals↗
PubMed1970

Sequential enzymes of linoleic acid oxidation in corn germ: lipoxygenase and linoleate hydroperoxide isomerase.

Linoleic acid oxidation catalyzed by lipoxygenase (lipoxidase) activity in extracts of defatted corn germ does not terminate in the product, linoleic acid hydroperoxide, unless the lipoxygenase is first partially purified. If purification is not attempted, the hydroperoxide product exists only as a barely detectable intermediate in the synthesis of three products. One of these was identified as 9-hydroxy-10-oxo-cis-12-octadecenoic acid formed from the hydroperoxide by the enzyme, linoleate hydroperoxide isomerase. Another product, 13-hydroxy-10-oxo-trans-11-octadecenoic acid, is believed to be formed by an isomerase also. The third product was the linoleate ester of one of the hydroxy-oxo-fatty acids, 9-(cis-9,cis-12-octadecadienoyl)-10-oxo-cis-12-octadecenoic acid. It is not known if the synthesis of the ester is enzyme-catalyzed. When a mixture of 13-hydroperoxy-cis-9,trans-11-octa-decadienoic acid and 9-hydroperoxy-trans-10,cis-12-octa-decadienoic acid from soybean lipoxygenase oxidation of linoleic acid was used as a substrate, 13-hydroxy-12-oxo-cis-9-octadecenoic acid and 9-hydroxy-12-oxo-trans-10-octadecenoic acid were formed as the major products of catalysis by linoleate hydroperoxide isomerase(s) from corn. Smaller quantities of 9-hydroxy-10-oxo-cis-12-octadecenoic acid and 13-hydroxy-10-oxo-trans-11-octadecenoic acid were also formed.

Chromatography↗
PubMed1982

[Phosphohexose isomerase in psoriasis].

--The authors study in psoriasis an enzyme of the glucolytic way, the Phospho-hexose-isomerase. --They find significant high levels in blood and damaged skin, while these were "normal" in healthy skin. --Phospho-hexose-isomerase acts as a biological marker in psoriasis, and acquires the significance of an active cellular proliferation. --The highest values are those of the erythrodermaes which become normal with clinical involution. --The authors suggest that psoriasis, by an exaggerated cellular division inhibition mechanism, metabolism is deviated in order to bring the energetic elements and substrate to form the new cell. --Phospho-hexose-isomerase is not specific of the malignant process.

Adolescent↗
PubMed1982

Prostaglandin endoperoxide E2 isomerase is dissociated from prostaglandin endoperoxide synthetase in the renal cortex.

The rate of arachidonic acid metabolism by prostaglandin (PG) endoperoxide synthetase by the rabbit renal cortex (approximately 200 pmol/mg of protein/min) is very slow compared to medulla (approximately 2000 pmol/mg/min). However, by using PGH2 as a substrate and limiting reaction times, we were able to directly measure the endoperoxide-dependent PGE2 isomerase and found that both the cortex and medulla possess high levels of this activity (approximately pmol/mg/min). The PG endoperoxide E2 isomerase is dependent on reduced glutathione, but not cysteine, and is inactivated by p-hydroxymercuribenzoate or boiling. Thus, the renal medulla appears to exhibit an efficient coupling of cyclooxygenase and PG endoperoxide E2 isomerase, whereas the cortex has a vast excess of endoperoxide-dependent enzyme.

Animals↗
PubMed1994

Perturbing the metal site in D-xylose isomerase. Effect of mutations of His-220 on enzyme stability.

The histidine residue at position 220 in the Streptomyces rubiginosus D-xylose isomerase is conserved in all D-xylose isomerases. The three-dimensional structure of D-xylose isomerase reveals that His-220 is part of the octahedral coordination sphere of M2, one of two metal ions (Mn2+) in the active site. This work describes the effects of replacing His-220 with Ser, Glu, Asn, and Lys. The consequences of these amino acid substitutions on enzyme activity, thermostability, and structure were analyzed by kinetic, denaturation, and crystallographic methods. The kcat values H220S, H220N, and H220E are only 0.3-0.5% of the wild-type values, and the Km for each of these mutant enzymes increased by 30-40-fold over the wild-type value. The mutant enzyme H220K did not exhibit any measurable activity. Thermal denaturation studies (Tm values) indicate that the H220S and H220N mutant enzymes are approximately 5-8 degrees C less stable than the wild-type enzyme, whereas H220E and H220K are 13-24 degrees C less stable than the wild-type enzyme. To analyze the molecular basis for this decreased thermostability, the crystal structures of the H220S, H220N, and H220E mutant enzymes complexed with Mn2+ have been determined at 1.95, 1.90, and 1.75 A, respectively. In the H220S structure, a water molecule effectively replaces the N epsilon-2 atom of the imidazole ring of His-220 and mediates the interaction between Mn2+ at the M2 site and Ser-220. A similar water-mediated interaction between the metal ion and Asn-220 is observed in H220N. No direct or water-mediated interactions between the carboxyl group of Glu-220 and the metal are observed in H220E. Whereas octahedral coordination is maintained for the metal at the M2 site in H220S and H220N, a pentahedral coordination with the metal at the M2 site is observed in H220E. Metal activation measurements support the observation that metal binding is perturbed and is responsible for thermal lability of His-220 mutants.

Aldose-Ketose Isomerases↗