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At least 775 records · Page 43Linked to original sources
PubMed1977

Esterase activity in the guinea pig thyroid under normal and pathological conditions (vitamin A deficiency) with special regard to cyst-like structures.

By use of different activators and inhibitors, TOCP(tri-o-cresyl phosphate), PCMB (parachloromercury benzoate), NiCl2, Pb(NO3)2, HgCl2, Hg(NO3)2, eserine and sodium taurocholate, it is shown that the esterase in the cyst cells and in group I cells of the guinea pig thyroid probably are A-esterase isoenzymes. The activity in the majority of cyst cells is considerably stronger than in the other thyroid epithelial cells, and it is resistant to Hg inactivation. Neither esterase type nor intensity of the reaction product is altered in group I-II or cyst cells during vitamin A-deficiency. When a normal diet is given, the esterase in all thyroid epithelial cells is very sensitive to sodium taurocholate, while in cyst cells it is rather resistant to this inhibitor at vitamin-A-deficiency.

Animals↗
PubMed1980

Structural parameters in the microsomal hydrolysis of 3-acyloxy-1, 4-benzodiazepines and the multiplicity of the esterases involved.

The biotransformation of several prodrug-type esters of centrally acting 1, 4-benzodiazepines was studied. Their rates of hydrolysis catalyzed by the hepatic microsomal fraction of mice were measured by pH-stat. The heterogeneity of the microsomal esterases was investigated with induction by phenobarbital and with inhibition by DFP. The resulting changes in esterase activity indicated that the phenyl-substituted esters separate from the homogenous sets of oxazepam and lorazepam esters. Regression analysis of the relative hydrolysis rates of the homogenous ester sets revealed a similar dependence on the steric ES the polar sigma* and hydrophobic deltaRM terms of the acyl moiety. The role of the polar term shows that a nucleophilic attack of the acyl moiety determines the hydrolysis. The role of hydrophobicity can be attributed to its interrelation with the steric parameter. The common equations for the aliphatic sters of oxazepam and larazepam suggest the similar nature of the esterases in question and the same catalytic mechanism. Different 3-acetoxy-1, 4-benzodiazepines were also synthetised and their maximal hydrolysis rates were quite different. This excludes the possibility that the deacylation step of the enzymes is rate-determining. Instead, our data suggest that acylation of the microsomal esterases is rate-limiting for the hydrolysis of the aliphatic esters of 3-OH-benzodiazepines.

Animals↗
PubMed2002

Exploitation of heterosis for carotenoid content in African marigold (Tagetes erecta L.) and its correlation with esterase polymorphism.

African marigold (Tagetes erecta L.), a major source of carotenoids, is also grown as a cut flower and a garden flower in addition to being grown for its medicinal values. We studied gene action, combining ability and heterosis, aiming at genetic improvement of T. erecta for enhanced carotenoid content in petals, and report for the first time that heterosis can be exploited for total carotenoids and its commercially important fractions. Total content of carotenoids and lutein appears to be governed by dominance (or non-additive) gene action, while content of xanthophyll esters is governed by both additive and dominance (or non-additive) gene actions. Specific combining ability variance was predominant for all the three traits. General and specific combining abilities and heterosis were highly significant. Heterobeltiosis was also positive. General combining ability (GCA) variances were not significantly correlated to performance per se. There was also no correlation between performance per se of normal petalled pollen parents and the performance of crosses made between male-sterile (female) and male-fertile (pollen) parents. These findings suggest that carotenoid content should not be the only criterion considered in the selection of parental lines. Studies on esterase in seeds and peroxidase in seedlings revealed a relatively high level of polymorphism in esterase with a total of 14 isoforms, whereas peroxidase showed low polymorphism. Similarity indices between different parental combinations, calculated based on seed esterase polymorphism, showed a significant negative correlation (r = -0.479, P = 0.05) with heterosis for carotenoid content. This indicates that the selection of parents with wider variation in their esterase profiles may possibly be exploited for genetic enhancement of carotenoids in T. erecta.

Asteraceae↗
PubMed2005

Biodegradation of dipropyl phthalate and toxicity of its degradation products: a comparison of Fusarium oxysporum f. sp. pisi cutinase and Candida cylindracea esterase.

The efficiency of two lypolytic enzymes (fungal cutinase, yeast esterase) in the degradation of dipropyl phthalate (DPrP) was investigated. The DPrP-degradation rate of fungal cutinase was surprisingly high, i.e., almost 70% of the initial DPrP (500 mg/l) was decomposed within 2.5 h and nearly 50% of the degraded DPrP disappeared within the initial 15 min. With the yeast esterase, despite the same concentration, more than 90% of the DPrP remained even after 3 days of treatment. During the enzymatic degradation of DPrP, several DPrP-derived compounds were detected and time-course changes in composition were also monitored. The final chemical composition after 3 days was significantly dependent on the enzyme used. During degradation with fungal cutinase, most DPrP was converted into 1,3-isobenzofurandione (IBF) by diester hydrolysis. However, in the degradation by yeast esterase, propyl methyl phthalate (PrMP) was produced in abundance in addition to IBF. The toxic effects of the final degradation products were investigated using various recombinant bioluminescent bacteria. As a result, the degradation products (including PrMP) from yeast esterase severely caused oxidative stress and damage to protein synthesis in bacterial cells, while in the fungal cutinase processes, DPrP was significantly degraded to non-toxic IBF after the extended period (3 days).

Biodegradation, Environmental↗
PubMed2005

Activation and antitumor activity of CPT-11 in plasma esterase-deficient mice.

PURPOSE: To examine the antitumor activity and the pharmacokinetics of CPT-11 (irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin) in a plasma esterase-deficient scid mouse model, bearing human tumor xenografts. EXPERIMENTAL DESIGN: Plasma carboxylesterase (CE)-deficient mice were bred with scid animals to develop a strain that would allow growth of human tumor xenografts. Following xenotransplantation, the effect of the plasma esterase on antitumor activity following CPT-11 administration was assessed. In addition, detailed pharmacokinetic studies examining plasma and biliary disposition of CPT-11 and its metabolites were performed. RESULTS: In mice lacking plasma carboxylesterase, the mean SN-38 systemic exposures were approximately fourfold less than that observed in control animals. Consistent with the pharmacokinetic data, four to fivefold more CPT-11 was required to induce regressions in human Rh30 xenografts grown in esterase-deficient scid mice, as opposed to those grown in scid animals. Additionally, the route of elimination of CPT-11, SN-38, and SN-38 glucuronide (SN-38G) was principally in the bile. CONCLUSIONS: The pharmacokinetic profile for CPT-11 and its metabolites in the esterase-deficient mice more closely reflects that seen in humans. Hence, these mice may represent a more accurate model for antitumor studies with this drug and other agents metabolized by CEs.

Animals↗
PubMed2005

[Esterase activity of human organotypic cornea construct (HCC) as in vitro model for permeation studies].

Organotypic cornea equivalents are used as in vitro models for permeation studies. Many ophthalmic drugs are applied as ester prodrugs to achieve a higher bioavailability. The esterase activity of three corneal human cell lines (epithelial, stromal, endothelial cells) as well as of excised porcine cornea, human donor cornea and human cornea construct (HCC) was investigated and compared. Esterase activity was determined using p-nitrophenyl acetate and hydrocortisone acetate (HCA) as esterase substrates. Hydrocortisone acetate permeation across porcine cornea, human donor cornea and HCC was studied in vitro using Franz-diffusion cells. Corneal epithelial cells showed the highest esterase activity and only small differences to keratocytes and endothelial cells were detectable. The permeation barrier properties of the different corneal tissues were very similar in the case of HCA permeation whereas HCA metabolism rates were in the ranking order of porcine cornea > HCC > human donor cornea. Permeation and metabolism studies indicate that the in vitro permeation model HCC is able to adequately convert hydrocortisone acetate to hydrocortisone.

Aged↗
PubMed2000

Uptake of pivaloyloxymethyl butyrate into leukemic cells and its intracellular esterase-catalyzed hydrolysis.

UNLABELLED: Pivaloyloxymethyl butyrate (AN-9), a butyric acid (BA) prodrug, exhibited low toxicity and significant anticancer activity in vitro and in vivo. The purpose of this study was to elucidate the basis for AN-9 increased anticancer activity compared to BA, by studying the uptake of BA and AN-9 into the cells. METHODS: The uptake rate and level of [14C]-AN-9 and [14C]-BA, labeled on the carboxylic moiety of BA, into HL-60 and MEL leukemic cell lines was measured. The cells were filtered and the retained radioactivity was determined. The dependence of the uptake on the activity of cellular esterases and membrane fluidity was investigated. RESULTS: The uptake level in cells incubated with [14C]-AN-9 increased rapidly, peaked after 30 min in MEL and 1 h in HL-60 cells, and declined thereafter. This decline could be attributed to the hydrolysis of AN-9 by cellular esterases and catabolism of the released BA to CO2. In cells pretreated with an esterase inhibitor and incubated with [14C]-AN-9, the reduction of radioactivity was less precipitous. In cells exposed to [14C]-BA, the intracellular radioactivity level was low and unaffected by treatment with an esterase inhibitor. The uptake of [14C]-AN-9 decreased significantly at 4 degrees C compared to that at 37 degrees C. CONCLUSION: The higher potency of AN-9 compared to BA could be at least partially attributed to the more rapid uptake of the lipophilic AN-9 and the release of BA in the cells.

Animals↗
PubMed1990

Native agarose-polyacrylamide gel electrophoresis allowing the detection of aminopeptidase, dehydrogenase, and esterase activities at the nanogram level: enzymatic patterns in some Frankia strains.

Nanogram amounts of soluble aminopeptidases, dehydrogenases, and esterases were detected by nondenaturing ultralow gelling point agarose-polyacrylamide gel electrophoresis (ULGA-PAGE). Cytosolic fractions from Frankia sp. were electrophoresed at 4 degrees C in the presence of Co2+, Zn2+, or Mg2+ ions. Then, aminopeptidases and esterases were revealed by simultaneous capture staining by using fast garnet GBC diazonium salt as the chromogenic coupling compound. Dehydrogenases were revealed by using nitro blue tetrazolium salt as electron acceptor. A variety of aminopeptidases, dehydrogenases, and esterases could be identified by their migration in ULGA-PAGE and by their sensitivities to NaCl, CoSO4, ZnSO4, and MgCl2 when assayed "ingel." The presence of agarose was essential for the detection of the complex enzyme patterns. The patterns were remarkably similar for the five Frankia strains isolated from Allocasuarina and Casuarina host plants and differed from those of Frankia strains isolated from Comptonia and Hippophaë host plants. A nomenclature is proposed for aminopeptidases and other Frankia enzymes. The richness of the Frankia amino-peptidases and esterases zymograms makes them adequate marker enzymes for taxonomical, genetic, or biochemical studies. Dehydrogenases might also be useful, although a more restricted number of bands were found with L-lactic and L-malic acid as substrates.

Actinomyces↗
PubMed1992

Human mitochondrial aldehyde dehydrogenase substrate specificity: comparison of esterase with dehydrogenase reaction.

Substrate specificity of human mitochondrial low Km aldehyde dehydrogenase (EC 1.2.1.3) E2 isozyme has been investigated employing p-nitrophenyl esters of acyl groups of two to six carbon atoms and comparing with that of aldehydes of one to eight carbon atoms. The esterase reaction was studied under three conditions: in the absence of coenzyme, in the presence of NAD (1 mM), and in the presence of NADH (160 microM). The maximal velocity of the esterase reaction with p-nitrophenyl acetate and propionate as substrates in the presence of NAD was 3.9-4.7 times faster than that of the dehydrogenase reaction. Under all other conditions the velocities of dehydrogenase and esterase reactions were similar; the lowest kcat was for p-nitrophenyl butyrate in the presence of NAD. Stimulation of esterase activity by coenzymes was confined to esters of short acyl chain length; with longer acyl chain lengths or increased bulkiness (p-nitrophenyl guanidinobenzoate) no effect or even inhibition was observed. Comparison of kinetic constants for esters demonstrates that p-nitrophenyl butyrate is the worst substrate of all esters tested, suggesting that the active site topography is uniquely unfavorable for p-nitrophenyl butyrate. This fact is, however, not reflected in kinetic constants for butyraldehyde, which is a good substrate. The substrate specificity profile as determined by comparison of kcat/Km ratios was found to be quite different for aldehydes and esters. For aldehydes kcat/Km ratios increased with the increase of chain length; with esters under all three conditions, a V-shaped curve was produced with a minimum at p-nitrophenyl butyrate.

Aldehyde Dehydrogenase↗
PubMed1988

Studies on cholesterol esterase in rat adipose tissue: comparison of substrates and regulation of the activity.

Efficiency of substrates for cholesterol esterase (EC 3.1.1.13) assay, and regulation of the activity were investigated in rat epididymal adipose tissue. The activity in the supernatant was activated by cyclic AMP-dependent protein kinase, cyclic AMP, ATP and Mg2+, both with micellar and liposomal substrates. However, the micellar substrate was more suitable for the assay than the liposomal with respect to Vmax and Km. Thus, the micellar substrate was employed. Pretreatment of the supernatant with exogenous cyclic AMP-dependent protein kinase enhanced the activity dose dependently, whereas that with cyclic AMP decreased the activity slightly. The cyclic AMP-dependent protein kinase activity in the assay mixture was within the range which can cause changes in cholesterol esterase activity. These results suggest that the amount of cyclic AMP-dependent protein kinase, rather than the cyclic AMP level, plays an important role in the regulation of cholesterol esterase in tissues with a high cholesterol esterase activity relative to the kinase activity, such as in adipose tissue.

Adenylyl Cyclases↗
PubMed1988

Inhibitors of sterol synthesis. Oleate ester of 5 alpha-cholest-8(14)-en-3 beta-ol-15-one as a substrate for pancreatic cholesterol esterase.

5 alpha-Cholest-8(14)-en-3 beta-yl-15-one oleate (15-ketosteryl oleate), the oleate ester of a compound with the capacity to lower serum cholesterol, was effectively hydrolyzed by partially purified porcine pancreatic cholesterol esterase with an apparent Km of 0.28 +/- 0.01 mM and a Vmax of 0.62 +/- 0.01 mumol/min per mg protein compared to an apparent Km of 0.19 +/- 0.02 mM and a Vmax of 0.37 +/- 0.02 mumol/min per mg protein for cholesteryl oleate. The 15-ketosteryl oleate was also hydrolyzed by highly purified rat pancreatic cholesterol esterase with an apparent Km of 0.20 +/- 0.01 mM and a Vmax of 86.7 +/- 3.0 mumol/min per mg protein compared to an apparent Km of 0.43 +/- 0.01 mM and a Vmax of 119.8 +/- 2.6 mumol/min per mg protein for cholesteryl oleate. 15-Ketosteryl oleate is, therefore, a good substrate for pancreatic cholesterol esterase from either source. The 15-ketosterol is a weak competitive inhibitor of partially purified porcine pancreatic cholesterol esterase when cholesteryl oleate is the substrate.

Animals↗
PubMed1991

Esterase activity of synthetic fragments of human adrenocorticotrophic hormone.

The anterior pituitary hormone adrenocorticotrophin (ACTH) has been extensively studied in terms of structure-function relationships and in vivo and in vitro activities of different synthetic fragments of ACTH have been characterized. Here we describe the ability of synthetic fragments of ACTH to hydrolyze a fluorogenic esterase substrate 4-methylumbelliferyloleate (MUBO). The measured esterase activities (in mumol 4-MU mol-1 s-1) were 79.7 for ACTH1-13, 385.9 for ACTH3-18, 503.0 for ACTH1-19, 1249.9 for ACTH1-24 D-ser3, and 1350 for ACTH1-24. Although the significance of the observed esterase activities in the actual molecular mechanisms of action of ACTH remains to be established it is worth noticing that the esterase activities of the different ACTH fragments closely parallel their reported ability to activate the brain lipase as well as their in vivo ability to induce steroidogenesis in adrenal cortex.

Adrenocorticotropic Hormone↗
PubMed1990

Multiple molecular forms and lectin interactions of organophosphate-sensitive plasma and liver esterases during development of the chick.

Liver and plasma acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase activities of the chick embryo and adult chickens were separated by sucrose density gradient sedimentation and further differentiated by their lectin affinities and organophosphate sensitivities. Changes in plasma cholinesterases during development indicated a characteristic shift in tetrameric (G4) isoforms from a slightly larger G4 AChE in the embryo to G4 BChE in the adult. These changes were not reflected in isoform patterns of liver homogenates, however. Interestingly, the time course of an increase in plasma BChE activity corresponded to the time course of a decrease in liver BChE activity, as if this enzyme was being mobilized and released. The distribution of liver esterases included both monomeric (G1) and G4 BChE and a large p-nitrophenylacetate (p-NPA) esterase activity that was separated into two main peaks by density gradient ultracentrifugation. The effects of organophosphate inhibitors indicated that the two liver p-NPA esterase activities may be regarded as carboxylesterases; however, these enzymes showed very different sensitivities to paraoxon and diisopropylfluorophosphate (DFP), with IC50 values differing by 3 and 4 orders of magnitude. Lectin affinity studies with multiple esterase forms suggested a heterogeneous group of glycoproteins that were packaged at different sites in the liver cell and were consistent with the presence of an intracellular precursor form to plasma BChE.

Animals↗
PubMed1993

Human xenobiotic metabolizing esterases in liver and blood.

Esterases in human liver microsomes hydrolysed fluazifop-butyl (Vmax 9.8 +/- 1.6 mumol/min/g tissue), paraoxon (Vmax 47.4 +/- 7.5 nmol/min/g tissue) and phenylacetate (Vmax 57 +/- 8 mumol/min/g tissue), whereas esterases found in the human liver cytosol hydrolysed fluazifop-butyl (Vmax 10.0 +/- 0.5 mumol/min/g tissue) and phenylacetate (Vmax 37 +/- 2.9 mumol/min/g tissue) but not paraoxon. Human plasma esterase hydrolysed fluazifop-butyl (Vmax 0.09 +/- 0.006 mumol/min/mL), paraoxon (Vmax 210 +/- 14 nmol/min/mL) and phenylacetate (Vmax 250 +/- 17 mumol/min/mL). Inhibitory studies using paraoxon, bis-nitrophenol phosphate and mercuric chloride indicated fluazifop-butyl hydrolysis involved carboxylesterase in liver microsomes and cytosol, and cholinesterase and carboxylesterase in plasma. Phenylacetate hydrolysis involved arylesterase in plasma, both arylesterase and carboxylesterase in liver microsomes and carboxylesterase in liver cytosol. Plasma hydrolysis is less important and overall esterase activity is lower in humans than in the rat which is therefore a poor model.

Adult↗
PubMed1993

Enhancement of hepatic microsomal esterase activity following soman pretreatment in guinea pigs.

Soman (pinacolyl methylphosphonofluoridate), a highly toxic organophosphate compound, has been found to be a strong inhibitor of hepatic microsomal carboxylesterase in vitro, but an enhancer of carboxylesterase when administered in vivo. In response to this paradoxical observation, the objective of this study was to determine if soman could cause true enhancement of the metabolism of drugs in the guinea pig and, if so, to characterize the enhanced enzyme activity. Following the pretreatment of guinea pigs with 90% LD50 soman, enhancement of microsomal esterase activity was noted 12 and 24 hr after pretreatment. Using Michaelis-Menten enzyme kinetic studies, enhancement was found to occur with liver carboxylesterase and procaine esterase, but not with aniline hydroxylase. Since the soman-enzyme complex was known to undergo aging with the release of pinacolyl alcohol and the subsequent formation of pinacolone, the effects of these metabolites on the activity of liver microsomal enzymes in vitro were explored. Pinacolone and pinacolyl alcohol produced enzyme enhancement in vitro in a manner similar to that produced by soman pretreatment. These effects were compared with those made by acetone in the same incubations, since the enhancing influence of acetone has already been well documented. Similarity was found between the in vitro effects of acetone and the effects of pinacolone and pinacolyl alcohol. Lastly, the in vivo effects of pinacolone on the activities of the same liver microsomal enzymes were studied following pretreatment of the guinea pigs with 90% LDLo (lowest published lethal dose) pinacolone. Pretreating guinea pigs with pinacolone prior to killing them enhanced liver microsomal carboxylesterase and procaine esterase activities, but had no effect on microsomal aniline hydroxylase activity. This pattern of enzyme enhancement was similar to that observed after soman pretreatment. Therefore, soman was found to enhance hepatic microsomal esterase activity in the guinea pig in a manner similar to that seen with its metabolites, as well as acetone. This information may give insight into how the efficacy and toxicity of therapeutic drugs, other xenobiotics, and endogenous materials may be altered in individuals who survive an exposure to soman.

Acetone↗
PubMed1988

Relationship between the covalent binding of N-acetoxy-2-acetylaminofluorene to DNA and a steroidal esterase activity in human mononuclear leukocytes.

A method for the quantitative assessment of steroidal esterase activity in viable human mononuclear leukocytes (HML) has been developed. It is based on estimating the conversion of [3H]beclomethasone-17,21-dipropionate (BDP) to beclomethasone-17-monopropionate (BMP) using TLC on silica gel 60 F-254 plates developed in a solvent system of chloroform/methanol (97:3, v/v). The cell assay procedure was dependent on BDP concentration, incubation time and cell concentration. The steroidal esterase activity was completed for by N-acetoxy-N-acetyl-2-aminofluorene (NA-AAF) and completely inhibited by 100 microM paraoxon. When [3H]NA-AAF binding to DNA was used as an indicator of HML esterase (deacylase) activity, BDP functioned as a substrate inhibitor. Parallel estimations of BDP metabolism and NA-AAF binding to DNA indicated striking correlations in the interindividual variations (r = 0.62, P less than 0.001) and in relation to the menstrual cycle events of a healthy female. Hence, these data indicate that both BDP and NA-AAF are metabolized by the same non-specific steroidal esterase present in HML.

2-Acetylaminofluorene↗
PubMed1993

The esterases: perspectives and problems.

Many proteins capable of hydrolysing esters are present in biological material of all kinds (microorganisms, plants, invertebrates and vertebrates). Some serve, as indicated by their substrate specificity and distribution within organisms, a defined biological function. However for most esterases a rather general substrate specificity is found indicating that they may have a broad biological function. Their properties will be briefly reviewed with particular emphasis on inhibitors. The mechanism of hydrolysis of esters by many carboxylesterases (B-esterases) is well established largely due to the reaction of OP compounds with their catalytic centre. For others, such as enzymes hydrolysing (i) OP compounds and/or (ii) carboxyl esters which are not inhibited by a time and temperature dependent reaction by OP compounds, reaction mechanisms are still conjecture. The purpose of this presentation is to explore similarities and differences between the esterases and to discuss possible routes for progress in the A-esterase group.

Animals↗
PubMed1978

Acid esterase activity in cultured skin fibroblasts and amniotic fluid cells using 4-methylumbelliferyl palmitate.

The properties and levels of acid esterase in cultured skin fibroblasts and amniotic fluid cells were investigated using 4-methylumbelliferyl palmitate as substrate. Determinations of acid esterase activity could be made using as little as 1 microgram cell protein. Cardiolipin increased the activity 2--3 fold at the pH optimum 4.0. The apparent KM for both cell types studied was 196 micrometer without and 96 micrometer with cardiolipin. Acid esterase activity was inhibited by cyanide and thiomersal, but not by iodoacetate and N-ethylmaleimide. However activation by cardiolipin was prevented by iodoacetate, N-ethylmaleimide and also sodium chloride. Skin fibroblasts and primary amniotic fluid cells had similar levels with or without cardiolipin. A cyclic activity was found with subculture but no consistent pattern with passage. The acid esterase deficiency in Wolman's and cholesterol ester storage diseases was demonstrated with this substrate.

Amniotic Fluid↗