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 901 records · Page 50Linked to original sources
PubMed1988

Coenzyme stimulation of isomerase activity of sepiapterin reductase in the biosynthesis of tetrahydrobiopterin.

The 6-lactoyl tetrahydropterin (C1'-keto PH4) isomerase activity of sepiapterin reductase, which was found in our recent work (Katoh and Sueoka (1987) J. Biochem. 101, 275-278) as a novel activity of the enzyme, i.e., the conversion of C1'-keto PH4 to 6-1'-hydroxy-2'-oxopropyl tetrahydropterin (C2'-keto PH4) without coenzymes, could be enhanced by a small amount of NADPH or NADP+. The concentration of NADP+ required for the maximal stimulation was approximately the same as the concentration of the enzyme subunit. When NADP+ was added with the enzyme and C1'-keto PH4 at pH 8.6, the reaction sequence of C1'-keto PH4----C2'-keto PH4----tetrahydrobiopterin (BH4) was observed in the presence of dithioerythritol. These observations suggest that the coenzyme stimulating the isomerase function of sepiapterin reductase may be involved in the two sequential reductions, from pyruvoyl tetrahydropterin to BH4, by causing internal rearrangement of the keto group of the first intermediate, C1'-keto PH4, to form the second one, C2'-keto PH4.

Alcohol Oxidoreductases↗
PubMed1989

Structural and functional differentiation of two clinally distributed glucosephosphate isomerase allelic isozymes from the teleost Fundulus heteroclitus.

The teleost Fundulus heteroclitus (L.) possesses two loci, Gpi-A and Gpi-B, for the glycolytic enzyme, glucose-phosphate isomerase (GPI; D-glucose-6-phosphate ketol-isomerase; E.C. 5.3.1.9). The Gpi-B locus is polymorphic in Fundulus, with two common alleles, Gpi-Bb and Gpi-Bc, distributed in a clinal manner in populations along the east coast of North America. Since this clinal distribution is strongly correlated with a temperature gradient, we asked whether the GPI-B2 allozymes were functionally adapted to the thermal environment in which a given phenotype predominated. The two major GPI-B2 allozymes were purified to homogeneity and were characterized as to molecular weight, isoelectric pH, thermal denaturation, and kinetic parameters. Both GPI-Bb2 and GPI-Bc2 allozymes have molecular masses of 110 kD, and they have isoelectric pHs of 6.4 and 6.6, respectively. The GPI-Bb2 allozyme was more stable to thermal denaturation than was the GPI-Bc2 enzyme. Kinetic properties of the allelic isozymes were investigated both as a function of pH and as a function of temperature. At 25 degrees C, over the pH range considered, there were no significant differences between allozymes, either in Km for fructose-6-phosphate or in Ki for 6-phosphogluconate, but apparent Vmax values differed between pH 7.5 and pH 8.5. All steady-state kinetic parameters showed strong temperature dependence, but the allozymes differed only in the Ki for 6-phosphogluconate at temperatures greater than 30 degrees C. On the basis of the observed structural and functional differences alluded to above, the hypothesis that the major allelic isozymes of the Gpi-B locus were functionally equivalent was rejected. However, it is not yet known whether these structural and functional differences have any significance at higher levels of biological organization.

Alleles↗
PubMed2003

Expression of a bacterial xylose isomerase in potato tubers results in an altered hexose composition and a consequent induction of metabolism.

Here we investigate the role of hexoses in the metabolism of the developing potato (Solanum tuberosum) tuber by the expression of a bacterial xylose isomerase which catalyzes the interconversion of glucose and fructose. Previously, we found that glycolysis was induced in transgenic tubers expressing a yeast invertase in the cytosol and postulated that this was due either to the decreased levels of sucrose or to effects downstream of the sucrose cleavage. In the present study xylose isomerase was expressed under the control of the tuber-specific patatin promoter. Selected transformants exhibited minor changes in the levels of tuber glucose and fructose but not in sucrose. Analysis of the enzyme activities of the glycolytic pathway revealed minor yet significant increases in the maximal catalytic activities of aldolase and glyceraldehyde 3-phosphate dehydrogenase but no increase in the activities of other enzymes of glycolysis. These lines were also characterized by an elevated tuber number, glycolytic and sucrose synthetic fluxes and in some metabolite levels downstream of glycolysis. When considered together these data suggest that the perturbation of hexose levels can result in increased glycolytic and sucrose (re)synthetic fluxes in the potato tuber even in the absence of changes in the level of sucrose. The consequences of altering hexose levels in the tuber are, however, not as severe as those observed following perturbation of the level of tuber sucrose.

Aldose-Ketose Isomerases↗
PubMed2005

ALBINO AND PALE GREEN 10 encodes BBMII isomerase involved in histidine biosynthesis in Arabidopsis thaliana.

We isolated an Arabidopsis albino and pale green 10 (apg10) mutant which exhibits pale green cotyledons and true leaves at the juvenile stage. We identified a valine to leucine change in BBMII (N'-[(5'-phosphoribosyl)-formimino]-5-aminoimidazole-4-carboxamide ribonucleotide) isomerase involved in histidine biosynthesis. The morphological abnormality of apg10 was recovered by histidine supplementation. The histidine limitation induced by apg10 mutation causes dynamic changes of the free amino acid profile, suggesting the existence of a cross-pathway regulatory mechanism of amino acid biosynthesis in plants. We also revealed that the APG10 knockout mutant exhibited embryo lethality, indicating the essential role of the Arabidopsis BBMII isomerase for plant growth.

Amino Acid Sequence↗
PubMed2002

Subunit interface mutation disrupting an aromatic cluster in Plasmodium falciparum triosephosphate isomerase: effect on dimer stability.

A mutation at the dimer interface of Plasmodium falciparum triosephosphate isomerase (PfTIM) was created by mutating a tyrosine residue at position 74, at the subunit interface, to glycine. Tyr74 is a critical residue, forming a part of an aromatic cluster at the interface. The resultant mutant, Y74G, was found to have considerably reduced stability compared with the wild-type protein (TIMWT). The mutant was found to be much less stable to denaturing agents such as urea and guanidinium chloride. Fluorescence and circular dichroism studies revealed that the Y74G mutant and TIMWT have similar spectroscopic properties, suggestive of similar folded structures. Further, the Y74G mutant also exhibited a concentration-dependent loss of enzymatic activity over the range 0.1-10 microM. In contrast, the wild-type enzyme did not show a concentration dependence of activity in this range. Fluorescence quenching of intrinsic tryptophan emission was much more efficient in case of Y74G than TIMWT, suggestive of greater exposure of Trp11, which lies adjacent to the dimer interface. Analytical gel filtration studies revealed that in Y74G, monomeric and dimeric species are in dynamic equilibrium, with the former predominating at low protein concentration. Spectroscopic studies established that the monomeric form of the mutant is largely folded. Low concentrations of urea also drive the equilibrium towards the monomeric form. These studies suggest that the replacement of tyrosine with a small residue at the interface of triosephosphate isomerase weakens the subunit-subunit interactions, giving rise to structured, but enzymatically inactive, monomers at low protein concentration.

Animals↗
PubMed2003

Directed evolution of Thermotoga neapolitana xylose isomerase: high activity on glucose at low temperature and low pH.

The Thermotoga neapolitana xylose isomerase (TNXI) is extremely thermostable and optimally active at 95 degrees C. Its derivative, TNXI Val185Thr (V185T), is the most active type II xylose isomerase reported, with a catalytic efficiency of 25.1 s(-1) mM(-1) toward glucose at 80 degrees C (pH 7.0). To further optimize TNXI's potential industrial utility, two rounds of random mutagenesis and low temperature/low pH activity screening were performed using the TNXI V185T-encoding gene as the template. Two highly active mutants were obtained, 3A2 (V185T/L282P) and 1F1 (V185T/L282P/F186S). 1F1 was more active than 3A2, which in turn was more active than TNXI V185T at all temperatures and pH values tested. 3A2 and 1F1's high activities at low temperatures were due to significantly lower activation energies (57 and 44 kJ/mol, respectively) than that of TNXI and V185T (87 kJ/mol). Mutation L282P introduced a kink in helix alpha7 of 3A2's (alpha/beta)8 barrel. Surprisingly, this mutation kinetically destabilized 3A2 only at pH 5.5. 1F1 displayed kinetic stability slightly above that of TNXI V185T. In 1F1, mutation F186S creates a cavity that disrupts a four-residue network of aromatic interactions. How the conformation of the neighboring residues is affected by this cavity and how these conformational changes increase 1F1's stability still remain unclear.

Aldose-Ketose Isomerases↗
PubMed1999

The wheat peptidyl prolyl cis-trans-isomerase FKBP77 is heat induced and developmentally regulated.

We isolated a cDNA encoding a 568-amino acid, heat-stress-induced peptidyl prolyl isomerase belonging to the FK506-binding-protein (FKBP) family. The open reading frame encodes for a peptidyl prolyl isomerase that possesses three FKBP-12-like domains, a putative tetratricopeptide motif, and a calmodulin-binding domain. Specific antibodies showed that the open reading frame encodes a heat-induced 77-kD protein, the wheat FKBP77 (wFKBP77), which exhibits 84% identity with the wFKBP73 and 42% identity with the human FKBP59. Because of the high similarity in sequence to wFKBP73, wFKBP77 was designated as the heat-induced isoform. The wFKBP77 mRNA steady-state level was 14-fold higher at 37 degreesC than at 25 degreesC. The wFKBP77 transcript abundance was the highest in mature embryos that had imbibed and 2-d-old green shoots exposed to 37 degreesC, and decreased to 6% in 6-d-old green shoots. The transcript level returned to the level detected at 25 degreesC after recovery of the embryos for 90 min at 25 degreesC. We compared wFKBP73 and wFKBP77 with the heat-shock proteins having cognate and heat-stress-induced counterparts.

Amino Acid Sequence↗
PubMed2002

Cloning of tangerine from tomato reveals a carotenoid isomerase essential for the production of beta-carotene and xanthophylls in plants.

Carotenoid biosynthesis in plants has been described at the molecular level for most of the biochemical steps in the pathway. However, the cis-trans isomerization of carotenoids, which is known to occur in vivo, has remained a mystery since its discovery five decades ago. To elucidate the molecular mechanism of carotenoid isomerization, we have taken a genetic map-based approach to clone the tangerine locus from tomato. Fruit of tangerine are orange and accumulate prolycopene (7Z,9Z,7'Z,9'Z-tetra-cis-lycopene) instead of the all-trans-lycopene, which normally is synthesized in the wild type. Our data indicate that the tangerine gene, designated CRTISO, encodes an authentic carotenoid isomerase that is required during carotenoid desaturation. CRTISO is a redox-type enzyme structurally related to the bacterial-type phytoene desaturase CRTI. Two alleles of tangerine have been investigated. In tangerine(mic), loss of function is attributable to a deletion mutation in CRTISO, and in tangerine(3183), expression of this gene is impaired. CRTISO from tomato is expressed in all green tissues but is upregulated during fruit ripening and in flowers. The function of carotene isomerase in plants presumably is to enable carotenoid biosynthesis to occur in the dark and in nonphotosynthetic tissues.

Alleles↗
PubMed1990

Refinement of glucose isomerase from Streptomyces albus at 1.65 A with data from an imaging plate.

The structure of 'metal-free' glucose isomerase of Streptomyces albus strain number YT ATCC 21132 has been analysed and refined at 1.65 A. The space group is I222, with cell dimensions a = 93.9 (1), b = 99.7 (1) and c = 102.9 (1) A, and there is one monomer of the tetrameric molecule per asymmetric unit. The data were recorded from two crystals of the protein using synchrotron radiation from the EMBL beamline X11 at DESY, Hamburg. Data were recorded with an imaging plate scanner designed and built in the EMBL Hamburg outstation. The total data-collection time was less than 12 h and the processing of all data took less than 2 days. The coordinates of the Arthrobacter glucose isomerase refined at a resolution of 2.5 A were used as a starting model. The structure of the protein and of 445 associated water molecules in the asymmetric unit were refined by restrained least-squares minimization using all data between 8 and 1.65 A to a final R factor of 14.1%.

Aldose-Ketose Isomerases↗
PubMed2003

The structure of human phosphoglucose isomerase complexed with a transition-state analogue.

Phosphoglucose isomerase (PGI) is a workhorse enzyme of carbohydrate metabolism that interconverts glucose 6-phosphate and fructose 6-phosphate. Outside the cell, however, the protein appears to function as a cytokine. A crystal structure of human PGI bound with 5-phosphoarabinonate, a strong inhibitor that mimics the cis-enediol(ate) intermediate of the reaction, has been determined at 2.5 A resolution. The structure helps to confirm the assignment of Glu357 as the base catalyst in the isomerase reaction.

Crystallization↗
PubMed2004

Leishmania mexicana mexicana glucose-6-phosphate isomerase: crystallization, molecular-replacement solution and inhibition.

Glucose-6-phosphate isomerase (PGI; EC 5.3.1.9; also often called by its old nomenclature phosphoglucose isomerase) is an intracellular enzyme that catalyses the reversible conversion of D-glucose 6-phosphate (G6P) to D-fructose 6-phosphate (F6P). The native Leishmania PGI is a homodimeric molecule of 60 kDa per monomer with 47% sequence identity to human PGI. It has been shown to be present in both the cytosol and the glycosome of Leishmania promastigotes and represents a potential target for rational drug design. The present work describes the crystallization of two bacterially expressed Leishmania PGI constructs, one corresponding to the natural protein and the other to an N-terminally deleted form. Crystals of both forms are identical and present a large c unit-cell parameter. A complete data set was collected from the N-terminally deleted PGI to a resolution of 3.3 A in space group P6(1), with unit-cell parameters a = b = 87.0, c = 354.7 A, alpha = beta = 90, gamma = 120 degrees. A preliminary study of the first inhibitors to be evaluated on the Leishmania enzyme is also reported.

Amino Acid Sequence↗
PubMed1999

A thermostable xylose isomerase from Thermus caldophilus: biochemical characterization, crystallization and preliminary X-ray analysis.

A highly thermostable xylose isomerase from Thermus caldophilus has been expressed in Escherichia coli. The purified enzyme has an optimum temperature of 363 K. It has been crystallized at room temperature using ammonium sulfate as a precipitant. The crystal belongs to the orthorhombic space group P212121, with unit-cell parameters a = 84.35, b = 123.60, c = 140.24 A. The presence of one molecule of tetrameric xylose isomerase in the asymmetric unit gives a crystal volume per protein mass (Vm) of 2.1 A3 Da-1 and a solvent content of 41% by volume. The crystals initially showed diffraction to 1.7 A Bragg spacing with synchrotron X-rays, and a set of native data extending to 2.3 A resolution has been collected.

Aldose-Ketose Isomerases↗
PubMed2006

Structure of ribose 5-phosphate isomerase from Plasmodium falciparum.

The structure of ribose 5-phosphate isomerase from Plasmodium falciparum, PFE0730c, has been determined by molecular replacement at 2.09 angstroms resolution. The enzyme, which catalyzes the isomerization reaction that interconverts ribose 5-phosphate and ribulose 5-phosphate, is a member of the pentose phosphate pathway. The P. falciparum enzyme belongs to the ribose 5-phosphate isomerase A family, Pfam family PF06562 (DUF1124), and is structurally similar to other members of the family.

Aldose-Ketose Isomerases↗
PubMed2004

Zinc-dependent dimerization of the folding catalyst, protein disulfide isomerase.

Protein disulfide isomerase (PDI), an essential folding catalyst and chaperone of the endoplasmic reticulum (ER), has four structural domains (a-b-b'-a'-) of approximately equal size. Each domain has sequence or structural homology with thioredoxin. Sedimentation equilibrium and velocity experiments show that PDI is an elongated monomer (axial ratio 5.7), suggesting that the four thioredoxin domains are extended. In the presence of physiological levels (<1 mM) of Zn(2+) and other thiophilic divalent cations such as Cd(2+) and Hg(2+), PDI forms a stable dimer that aggregates into much larger oligomeric forms with time. The dimer is also elongated (axial ratio 7.1). Oligomerization involves the interaction of Zn(2+) with the cysteines of PDI. PDI has active sites in the N-terminal (a) and C-terminal (a')thioredoxin domains, each with two cysteines (CGHC). Two other cysteines are found in one of the internal domains (b'). Cysteine to serine mutations show that Zn(2+)-dependent dimerization occurs predominantly by bridging an active site cysteine from either one of the active sites with one of the cysteines in the internal domain (b'). The dimer incorporates two atoms of Zn(2+) and exhibits 50% of the isomerase activity of PDI. At longer times and higher PDI concentrations, the dimer forms oligomers and aggregates of high molecular weight (>600 kDa). Because of a very high concentration of PDI in the ER, its interaction with divalent ions could play a role in regulating the effective concentration of these metal ions, protecting against metal toxicity, or affecting the activity of other (ER) proteins that use Zn(2+) as a cofactor.

Amino Acid Substitution↗
PubMed1992

Characterization, expression, and immunohistochemical localization of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in human skin.

Three beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyses an obligatory step in the biosynthesis of all classes of hormonal steroids, namely, the oxidation/isomerization of 3 beta-hydroxy-5-ene steroids into the corresponding 3-keto-4-ene steroids in gonadal as well as in peripheral tissues. Because humans are unique with some primates in having adrenals that secrete large amounts of the steroid precursors dehydropiandrosterone (DHEA) and its sulfate (DHEA-S) and its exceptionally large volume makes the skin an important site of steroid biosynthesis, we have isolated and characterized cDNA clones encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase from a human skin lambda gt11 library. The longest clone obtained contains the entire coding sequence for type I 3 beta-HSD (372 amino acids) as well as an additional 131 nucleotides in the 5'-untranslated region. The insert of 1647 bp containing the entire coding region has been inserted in a pCMV expression vector and transfected into human cervical carcinoma cells (HeLa). The expressed enzyme efficiently catalyzes the transformation of pregnenolone, DHEA, and dihydrotestosterone into progesterone, 4-androstenedione, and 5 alpha-androstane-3 beta, 17 beta-diol, respectively. Using the enzyme expressed in HeLa cells, we have shown cyproterone acetate, a progestin used in the treatment of acne and hirsutism, as well as norgestrel and norethindrone, two steroids widely used as oral contraceptives, to be relatively potent inhibitors, with Ki values of 0.38 microM, 1.3 microM, and 1.2 microM, respectively. Immunohistochemical localization of 3 beta-HSD, illustrated by using an antibody raised against human placental 3 beta-HSD, shows that the enzyme is localized in sebaceous glands.

Amino Acid Sequence↗
PubMed1984

Sugar synthesis in Leptospira. I. Presence of glucosephosphate isomerase.

The presence of glucosephosphate isomerase, one of the key enzymes in carbohydrate metabolism, was confirmed for the first time in the cell-free extract of Leptospira biflexa. The glucosephosphate isomerase of L. biflexa was heat-labile and its optimum pH was about 8.5. The enzyme showed an optimal temperature of about 45 C but was more stable at 30 C. Km value of the enzyme was 5.6 X 10(-3)M. The activity of the enzyme was inhibited by the inhibitor, 6-phosphogluconate. From this study, the presence of a metabolic pathway, the phosphogluconate pathway, other than non-oxidative pentose phosphate pathway presented by Baseman and Cox was suggested.

Citric Acid Cycle↗
PubMed1977

Genetic variants of glucose phosphate isomerase (E.C. 5.3.1.9) in canine erythrocytes.

Genetic polymorphism of glucose phosphate isomerase (GPI) was found in the erythrocytes of dogs of six Japanese breeds by using starch gel electrophoresis. Analysis of parentage records of dogs revealed that the phenotypic variation of erythrocyte glucose phosphate isomerase was controlled by one autosomal locus with two codominant alleles, GPIA and GPIB. The allele GPIB was observed in the following breeds: San'in-Shiba, Shinshu-Shiba, Shikoku, Kai and Kishu, but not in Hokkaidoes and Akitas. All the dogs belonging to 25 European breeds, 5 oriental or China-origin (except Japan) breeds examined in this experiments had the genotype constitution GPIA/GPIA, whereas one Dalmation dog was heterozygous GPIA/GPIB.

Alleles↗