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At least 1,603 records · Page 89Linked to original sources
PubMed1998

Detection of a new enzyme for stereoselective hydrolysis of linalyl acetate using simple plate assays for the characterization of cloned esterases from Burkholderia gladioli.

Plate assays were developed for the identification of specific hydrolytic activities of esterases from Burkholderia gladioli, cloned and expressed in Escherichia coli. Clones showing different substrate specificities were identified by fluorescence or azo-dye formation caused by the released alcohol moiety of the hydrolyzed substrates, or by colour change of pH indicators mediated by decreased pH. The use of 1-hydroxypyrene-3,6,8-trisulfonic acid (HPTS-) esters and linalyl acetate for these assays clearly allowed to discriminate substrate specificities for two different cloned esterases, EP6 and EP10. Long chain fatty acid HPTS-esters were only hydrolyzed by the EP10 clone. On the other hand, the EP6 clone showed significant activity in hydrolysis of the sterically hindered ester linalyl-acetate. Enantioselective hydrolysis of linalyl acetate could be verified with a crude EP6 preparation on a preparative scale.

Burkholderia↗
PubMed1981

Identification of the esterase peptide and its interaction with the cheZ peptide in bacterial sensing.

Previous genetic evidence has indicated that the methylesterase activity of the chemotaxis system in Escherichia coli and Salmonella typhimurium resides with the cheB gene product, and that this protein may interact with the cheZ protein. In this article we report biochemical evidence for association of the cheB protein with esterase activity. We also show that while the cheZ gene product is not needed for catalysis, certain mutations in it can eliminate esterase activity in vitro, suggesting association of cheZ and cheB in an oligomeric protein complex.

Chemotaxis↗
PubMed2003

Effect of trifluoroethanol on the conformational stability of a hyperthermophilic esterase: a CD study.

The conformational stability of the hyperthermophilic esterase AFEST from Archeoglobus fulgidus against the denaturing action of 2,2,2-trifluoroethanol (TFE) has been investigated by means of circular dichroism (CD) measurements. At room temperature far-UV and near-UV CD spectra point out the occurrence of a co-operative transition from the native structure to a denatured state characterized by a high content of alpha-helix. The TFE concentration at half-completion of the transition proves to be 3.5 M (25% v v(-1)), by recording the molar ellipticity at both 222 and 276 nm. Thermal transition curves of AFEST in the absence and in the presence of TFE indicate a significant stability decrease on increasing the TFE concentration. The denaturation temperature is 99 degrees C for native AFEST, but becomes 85 degrees C at 1.4 M TFE (10% v v(-1)), and 56 degrees C at 2.8 M TFE (20% v v(-1)). It is also shown that, even though AFEST is very resistant to temperature, its resistance towards the denaturing action of TFE is similar to that of mesophilic proteins, including an esterase from Escherichia coli, AES. The proposal of a general mechanism for the TFE action on globular proteins leads to a reliable rationale of experimental data.

Animals↗
PubMed1998

Effect of phenobarbital and beta-naphthoflavone on activities of different rat esterases after paraoxon exposure.

1. The effects of two model inducers of the cytochrome P450 system, phenobarbital (PB) and beta-naphthoflavone (NF), on the toxicity of paraoxon were studied in rats. 2. Paraoxon toxicity was measured by inhibition of brain acetylcholinesterase (AChE) activity. 3. PB treatment did not affect the toxicity of paraoxon, whereas NF increased the inhibition of brain AChE. PB administration slightly increased the activities of some peripheral cholinesterases and carboxylesterases, as well as liver microsomal paraoxonase (Pxase). 4. NF administration, in contrast, decreased the activities of peripheral esterases. Serum Pxase activity was reduced by both inducers. 5. Hepatic CYP2B and CYP1A were markedly induced by PB and NF, respectively. 6. Cytochrome P450 isoenzymes induced by PB or NF seemed not to be critical in the detoxification of paraoxon in vivo. NF caused a general reduction of peripheral esterases, which led to an increase in paraoxon toxicity. 7. The results indicated the great importance of peripheral cholinesterases and carboxylesterases as a detoxifying mechanism of paraoxon. The role of serum paraoxonase was not critical.

Animals↗
PubMed1977

[Frequency of genes corresponding to adenosine deaminase, 6-phosphogluconate dehydrogenase and esterase D polymorphism in the Parisian population].

The frequencies of the genes expressing the variation of erythrocytic enzymes ADA, 6PGD and esterase D have been estimated in Paris population. These results are as follows: (formula see text). These are compared to those of other european populations. Although ADA shows the lowest frequency in the french population, the distribution is not significantly different from the whole european distribution. No difference is noticeable for 6PGD and esterase D.

Adenosine Deaminase↗
PubMed1983

Demonstration of T lymphocytes in leprous granuloma using the acid alpha naphtyl acetate esterase activity. An attempt at quantitative analysis.

In nine leprosy patients (1 TT, 1 BT, 4 BL and 3 LLp), esterase positive lymphocytes (T Lymphocytes) were studied in frozen sections of skin biopsies by alpha naphtyl acetate esterase pH 5.8 method (ANAE) Four patients had never been treated previously and five patients exhibited clinical and bacteriological evidence of relapse for inadequate therapy at first biopsy. There was an increase in ANAE (+) lymphocyte density in granulomas when second biopsies were done after efficient treatment, evaluated by bacillary index for the eight bacilliferous patients, and clinical improvement. The significance of T cells in granulomas is discussed.

Adult↗
PubMed2000

Prodrug to probe solution HFA pMDI formulation and pulmonary esterase activity.

A novel salbutamol prodrug was synthesised. Solubility in HFA-134a and susceptibility to rat lung homogenate, blood and plasma esterase enzymes were investigated. Whereas salbutamol had a very low solubility in HFA-134a, the prodrug was found to be miscible in all proportions. In lung homogenate, the prodrug hydrolysed with a half-life of 45 min, re-generating approximately 17% of expected salbutamol after 8 h incubation. The use of a solution pMDI for pulmonary delivery of the salbutamol prodrug is predicted to result in liberation of salbutamol in the lungs following in vivo hydrolysis by lung esterases.

Aerosol Propellants↗
PubMed1997

Peroxide treatment changes activity of non specific esterase in vascular endothelium of isolated pig aorta in vitro.

The effect of hydrogen peroxide on certain enzymes contained in endothelial cells was investigated in vitro. Specifically in this study the influence of hydrogen peroxide on the non-specific esterase activity in endothelial cells of the perfused pig aorta was examined. We perfused an isolated segment of the pig aorta for 10 h and added 5, 10, 12, 15 ml 10% hydrogen peroxide to 100 ml perfused medium. In unperfused pig aorta 99.34% of the endothelial cells reacted positive. After 10 h of perfusion without hydrogen peroxide administration 93.25% endothelial cells still showed positive enzyme reactivity. In presence of hydrogen peroxide in the perfusion medium the activity of non-specific esterase was progressively inhibited, finally causing complete inactivation.

Adenosine Triphosphatases↗
PubMed2000

Identification of a point mutation in an esterase gene in different populations of the southern cattle tick, Boophilus microplus.

Two esterase cDNA sequences were obtained from susceptible and organophosphorus resistant strains of Boophilus microplus. Both sequences have a high degree of homology to carboxylesterase B. One gene has identical sequences in both strains and the other showed two point mutations. One mutation produces an amino acid substitution when the amino acid sequence is deduced, this mutation was detected in six different populations susceptible and resistant to insecticides, but a pyrethroid resistant strain was the only one that showed only the mutant allele. Identification of this mutation and the strong signal detected in southern blot with this strain, suggest that esterases are contributing to detoxification of pyrethroid compounds, as a resistant mechanism in Mexican strains of the southern cattle tick.

Amino Acid Sequence↗
PubMed2002

Cloning of putative odorant-degrading enzyme and integumental esterase cDNAs from the wild silkmoth, Antheraea polyphemus.

Odorant-degrading enzymes have been postulated to participate in the fast deactivation of insect pheromones. These proteins are expressed specifically in the sensillar lymph of insect antennae in such low amounts that, hitherto, isolation and protein-based cDNA cloning has not been possible. Using degenerate primers based on conserved amino acid sequences of insect carboxylesterases and juvenile hormone esterases, we were able to amplify partial cDNA fragments, which were then used for the design of gene-specific primers for RACE. This bioinformatics approach led us to the cloning of cDNAs, encoding a putative odorant-degrading enzyme (Apol-ODE) and a putative integumental esterase (Apol-IE) from the wild silkmoth, Antheraea polyphemus. Apol-ODE had a predicted molecular mass of 59,994 Da, pI of 6.63, three potential N-glycosylation sites, and a putative catalytic site Ser characterized by the sequence Gly(195)-Glu-Ser-Ala-Gly-Ala. Apol-IE gave calculated molecular mass of 61,694 Da, pI of 7.49, two potential N-glycosylation sites, and a putative active site with the sequence Gly(214)-Tyr-Ser-Ala-Gly. The transcript of Apol-ODE was detected by RT-PCR in male antennae and branches (sensillar tissues), but not in female antennae and other control tissues. Apol-IE was detected in male and female antennae as well as legs.

Amino Acid Sequence↗
PubMed2000

Quantitative structure-activity relationships for the pre-steady-state inhibition of cholesterol esterase by 4-nitrophenyl-N-substituted carbamates.

4-Nitrophenyl-N-substituted carbamates (1-6) are the pseudo-substrate inhibitors of porcine pancreatic cholesterol esterase. Thus, the first step of the inhibition (Ki step) is the formation of the enzyme inhibitor tetrahedral adduct and the second step of the inhibition (kc) is the formation of the carbamyl enzyme. The formation of the enzyme inhibitor tetrahedral adduct is further divided into two steps, the formation of the enzyme-inhibitor complex with the dissociation constant, KS, at the first step and the formation of the enzyme-inhibitor tetrahedral adduct from the complex at the second step. The two-step mechanism for the formation of the enzyme-inhibitor tetrahedral adduct is confirmed by the pre-steady-state kinetics. The results of quantitative structure-activity relationships for the pre-steady-state inhibitions of cholesterol esterase by carbamates 1-6 indicate that values of -logKs and logk2/k-2 are correlated with the Taft substituent constant, sigma*, and the rho* values from these correlations are -0.33 and 0.1, respectively. The negative rho* value for the -logKS-sigma*-correlation indicates that the first step of the two-step formation of the enzyme-inhibitor tetrahedral adduct (KS step) is the formation of the positive enzyme inhibitor complex. The positive rho* value for the logk2/k-2 -sigma*-correlation indicates that the enzyme inhibitor tetrahedral adduct is more negative than the enzyme inhibitor complex. Finally, the two-step mechanism for the formation of the enzyme inhibitor tetrahedral adduct is proposed according to these results. Thus, the partially positive charge is developed at nitrogen of carbamates 1-6 in the enzyme-inhibitor complex probably due to the hydrogen bonding between the lone pair of nitrogen of carbamates 1-6 and the amide hydrogen of the oxyanion hole of the enzyme. The second step of the two-step formation of the enzyme-inhibitor tetrahedral adduct is the nucleophilic attack of the serine of the enzyme to the carbonyl group of carbamates 1-6 in the enzyme-inhibitor complex and develops the negative-charged oxygen in the adduct.

Animals↗
PubMed1999

Directed evolution of an esterase: screening of enzyme libraries based on pH-indicators and a growth assay.

In order to resolve a sterically hindered 3-hydroxy ethyl ester, which was not accepted as substrate by 20 wild-type hydrolases, a directed evolution of an esterase from Pseudomonas fluorescens (PFE) was performed. Mutations were introduced using the mutator strain Epicurian coli XL1-Red. Enzyme libraries derived from seven mutation cycles were assayed on minimal media agar plates supplemented with pH indicators (neutral red and crystal violet), thus allowing the identification of active esterase variants by the formation of a red color caused by a pH decrease due to the released acid. A further selection criteria was introduced by using the corresponding glycerol estar, because release of the carbon source glycerol facilitates growth on minimal media. By this strategy, one double mutant (A209D and L181V) of PFE was identified, which hydrolyzed the 3-hydroxy ethyl ester in a stereoselective manner (25% ee for the remaining ester, E approximate to 5).

Cell Division↗
PubMed2003

Construction and characterization of a recombinant esterase with high activity and enantioselectivity to (S)-ketoprofen ethyl ester.

The ester-hydrolyzing enzyme families, including lipase and esterase, mediated a broad range of reactions and, thus, were able to act on a variety of ester compounds that are found naturally or exploited industrially. With the increasing demand for pharmacological use, attempts to produce an enantiomer (S)-ketoprofen from the corresponding ethyl ester have recently been proliferating, but information about the structure and function of related enzymes has not been reported to date in detail. Here, we reported the construction, expression, and one-step purification of a potential esterase in Escherichia coli with a hexahistidine tag at its N-terminus. The expression level of the enzyme was more than 20% of the total protein in E. coli, resulting in approximately 1.2mg of the purified proteins by an affinity resin, Ni-NTA, from a 0.2L of bacterial culture in a single step. As typical properties, its innate traits that revealed favorable reactions at alkaline pH and high activity to the triglycerides composed of short chain fatty acids ( 99% ee(p)). The small-scale conversion using the recombinant enzyme strongly suggested the enzyme to be useful for enzyme-mediated chiral resolution of (S)-ketoprofen.

Amino Acid Sequence↗
PubMed1983

Histochemical localization of esterases in Avitellina lahorea Woodland, 1927 (Cestoda: Anoplocephalida).

Specific and non-specific esterases have been localized in sections and whole mounts of Avitellina lahorea, an intestinal parasite of sheep and goats. Non-specific esterases (NSE) were found in the sucker muscles, post-acetabular ganglia, nerve trunks, tegument, excretory canals, cirrus sac, vagina, uterus and the inner membrane of the embryophore. Acetylcholinesterase (AChE) was observed in all the above organs, including vas deferens and sperm ducts, but was absent from excretory canals and eggs. Tests with acetylthiocholine iodide (AThChI) revealed the nervous system, vas deferens, sperm ducts, uterus, cirrus sac and the vagina. The intensity of activity of AChE and AThChI was weak compared to NSE.

Acetylcholinesterase↗
PubMed1989

Esterase electrophoresis: a molecular tool for studying the epidemiology of Branhamella catarrhalis nosocomial infection.

A new epidemiologic typing method based on electrophoresis of esterases had been developed for differentiating between clinical isolates of Branhamella catarrhalis. Twenty-two epidemiologically significant strains obtained from three Chest Units, a Paediatric Intensive Care Unit and a Paediatric Unit were compared with 54 randomly selected strains and 4 reference strains, including the species type strain, ATCC 25238. Thirty-four distinct zymotypes were characterized by polyacrylamide-agarose gel electrophoresis of the 80 strains. One infrequent zymotype was found in 2 neonates and another in 2 adults with nosocomial bronchopulmonary infections, suggesting the nosocomial spread of 2 outbreak strains of B. catarrhalis. A more frequent zymotype was isolated from 3 neonates with nosocomial bronchopulmonary infection and from 2 children with nosocomial rhinopharyngitis. The remaining 12 epidemiologically significant strains were of varied zymotypes. This work demonstrates that esterase electrophoresis is a suitable, readily reproducible, stable typing system applicable to the wide range of strains found in B. catarrhalis nosocomial infections.

Adult↗
PubMed1993

Cholesterol transport function of pancreatic cholesterol esterase: directed sterol uptake and esterification in enterocytes.

We have recently hypothesized that neutral lipids can, in part, move across biological membranes via a mechanism involving enzymes anchored to membrane proteoglycans such as those found in the brush border of the enterocyte [Bosner, M. S., Gulick, T., Riley, D. J. S., Spilburg, C. A., & Lange, L. G. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7438-7442]. Present results now show a subsequent, essential protein-mediated sorting of neutral lipids for further intracellular metabolism. Thus, in the absence of enzyme, 0.002 pmol of cellular ester appeared after 2 h, and its level increased only 3.5-fold after 12 h. However, in the presence of cholesterol esterase, the level of cholesterol ester increased 39-fold in the same time period, indicating that the enzyme-mediated uptake accounts for 10-fold greater ester synthesis than that from basal absorption. Kinetic analysis reveals that both enzyme-mediated and background absorption depend on taurocholate concentration and are second-order reactions more likely dependent on collision than diffusion. Other lipid-recognizing proteins such as pancreatic triglyceride lipase and the intestinal fatty acid binding protein are not stimulatory to intracellular cholesterol processing. Taken together, these data suggest that pancreatic cholesterol esterase and possibly other proteoglycan-binding extracellular enzymes of neutral lipid metabolism may facilitate movement of neutral lipids into the plasma membrane and direct them into functional intracellular sites.

Animals↗
PubMed2002

Temperature- and denaturant-induced unfolding of two thermophilic esterases.

We studied the temperature- and denaturant-induced denaturation of two thermophilic esterases, AFEST from Archeoglobus fulgidus and EST2 from Alicyclobacillus acidocaldarius, by means of circular dichroism measurements. Both enzymes showed a very high denaturation temperature: 99 degrees C for AFEST and 91 degrees C for EST2. They also showed a remarkable resistance against urea; at half-completion of the transition the urea concentration was 7.1 M for AFEST and 5.9 M for EST2. On the contrary, both enzymes showed a weak resistance against GuHCl; at half-completion of the transition the GuHCl concentration was 2.0 M for AFEST and 1.9 M for EST2. The thermodynamic parameters characterizing urea- and GuHCl-induced denaturation of the studied enzymes have been obtained by both the linear extrapolation model and the denaturant binding model. The dependence of the thermal stability on NaCl concentration for both esterases has also been determined. A careful analysis of the data, coupled with available structural information, has allowed the proposal of a reliable interpretation.

Bacillus↗
PubMed2005

Esterase-activated two-fluorophore system for ratiometric sensing of biological zinc(II).

Intracellular ester hydrolysis by cytosolic esterases is a common strategy used to trap fluorescent sensors within the cell. We have prepared analogues of Zinpyr-1 (ZP1), an intensity-based fluorescent sensor for Zn2+, that are linked via an amido-ester or diester moiety to a calibrating fluorophore, coumarin 343. These compounds, designated Coumazin-1 and -2, are nonpolar and are quenched by intramolecular interactions between the two fluorophores. Esterase-catalyzed hydrolysis generates a Zn2+-sensitive ZP1-like fluorophore and a Zn2+-insensitive coumarin as a calibrating fluorophore. Upon excitation of the fluorophores, coumarin 343 emission relays information concerning sensor concentration whereas ZP1 emission indicates the relative concentration of Zn2+-bound sensor. This approach enables intracellular monitoring of total sensor concentration and provides a ratiometric system for sensing biological zinc ion.

Animals↗