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PubMed1986

The effect of bulk hydrogen ion concentration upon the apparent kinetic parameters of purified pig liver catechol O-methyltransferase.

In order to investigate the pH dependence of catechol O-methyltransferase (S-adenosyl-L-methionine:catechol O-methyltransferase, EC 2.1.1.6), kinetic parameters have been determined for the highly purified enzyme from pig liver over the pH range 6.75-8.20 using the substrates S-adenosylmethionine (AdoMet) and 3,4-dihydroxyphenylacetic acid (DOPAC). The Km for AdoMet was found to be invariant with pH while the Km for DOPAC decreased sharply with increasing pH. The group responsible for the latter has a pK of approx. 7.1. The logarithmic (Dixon) plot of Km against pH for both substrates and that of Vmax/Km against pH for DOPAC mirror the kinetic behaviour revealed by linear plots. However, for other parameters, linear graphs indicate peaks too narrow to be explicable by a simple kinetic mechanism, whereas logarithmic plots of these parameters produce graphs apparently not reflecting this behaviour. We conclude that these results are not the products of random error or artefactual data analysis but are too complex to be explicable by a simple model of kinetic behaviour. Possible explanations (adherence of catechol O-methyltransferase to a higher-order mechanism or a dual mode of substrate binding) are advanced.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1995

Sequence of the hpcC and hpcG genes of the meta-fission homoprotocatechuic acid pathway of Escherichia coli C: nearly 40% amino-acid identity with the analogous enzymes of the catechol pathway.

The meta-fission pathway for homoprotocatechuic acid (HPC) catabolism is chemically analogous to the oxidative meta-fission pathway for catechol degradation and so provides an opportunity to investigate how the enzymes of chemically similar, but specific, pathways might have arisen. Two more genes of the HPC pathway from Escherichia coli C, hpcC, encoding 5-carboxymethyl-2-hydroxymuconic acid semialdehyde (CHMS) dehydrogenase, and hpcG, encoding 2-oxohept-3-ene-1,7-dioic acid (OHED) hydratase, have now been sequenced to aid this analysis. The CHMS dehydrogenase showed 40% amino acid (aa) sequence identity with the corresponding enzyme of the catechol pathway, and the OHED hydratase showed 36% aa sequence identity with the catechol pathway hydratase. The CHMS dehydrogenase is a member of the aldehyde dehydrogenase superfamily that includes enzymes from animal, plant and microbial sources. Since it appears that the dioxygenase, isomerase and decarboxylase enzymes of the two pathways are not closely related, it is proposed that the two sets of enzymes have arisen separately, but with the muconic acid semialdehyde dehydrogenases and the hydratases being recruited, respectively, from the same ancestral sources.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1994

Improved assay for plasma dihydroxyphenylacetic acid and other catechols using high-performance liquid chromatography with electrochemical detection.

Several modifications of an HPLC-electrochemical assay method for plasma levels of norepinephrine (NE), epinephrine (EPI), dopamine (DA), dihydroxyphenylglycol (DHPG), dihydroxyphenylalanine (DOPA) and dihydroxyphenylacetic acid (DOPAC) that improve the accuracy and reliability of DHPG, DOPA, and DOPAC measurements are described. In batch alumina extractions, increasing the amount of alumina decreased analytical recoveries of DHPG, DOPA, and especially DOPAC, and increasing the strength of the eluting acid increased recoveries of these catechols, without affecting recoveries of the amines NE, EPI and DA. Refrigeration (4 degrees C) until injection stabilized DOPAC in aqueous solution and therefore improved the reproducibility of plasma DOPAC measurements. Circulation of chilled water (15 degrees C) around the column using a water jacket decreased variability in retention times of the catechols and thereby facilitated identification of peaks, while enhancing separation of DHPG from the solvent front. Use of 6-fluoro-DOPA and 6-fluoro-DOPAC as internal standards did not improve inter-assay reliability. We recommend that in assays of plasma catechols including DOPAC, small (5 mg), precisely measured amounts of alumina be used, with a relatively strong eluting solution (e.g. 0.04 M phosphoric acid-0.2 M acetic acid, 20:80, v/v), and that the samples be refrigerated until injection, with column temperature held constant at less than 20 degrees C.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2005

Characterization of two new variants of human catechol O-methyltransferase in vitro.

Catechol O-methyltransferase (COMT) plays an important role in the inactivation of biologically active and toxic catechols. It has been shown that human soluble COMT (S-COMT) is genetically polymorphic with a wild type and at least one variant in which a valine has been substituted with a methionine at codon 108. This polymorphism has been the subject of intense molecular epidemiological studies because of the important role of COMT in the metabolism of catecholamines and catechol estrogens. Several epidemiological studies have shown that women, homozygous with the Val108Met variant, have an increased risk of developing estrogen-associated cancers. However, some other studies have shown that this COMT polymorphism is not associated with increased risk of developing cancers. These conflicting data suggest that additional COMT genetic variants might contribute to the increased risk of developing cancers. Although two new single nucleotide polymorphisms (SNP) that cause amino acid substitutions Ala22Ser and Ala52Thr have been identified recently, they have not been fully characterized. In the present study, Ala22Ser and Ala52Thr variants of human S-COMT were produced using recombinant DNA techniques, and then COMT properties were measured including enzymatic activity, thermostability, and sensitivity to inhibition mediated by 4-hydroxyequilenin (4-OHEN). The Ala22Ser variant showed lower methylation capacity and higher thermolability. In addition, this variant is sensitive to 4-OHEN mediated irreversible inhibition. Our data indicate that the Ala22Ser polymorphism might also be of functional significance and might play a role in susceptibility to estrogen-associated cancers.

Alanine↗
PubMed2004

The effects of benzene and the metabolites phenol and catechol on c-Myb and Pim-1 signaling in HD3 cells.

Exposure to the environmental toxicant benzene has been proposed to lead to leukemogenesis. The transcription factor c-Myb plays a role in blood cell differentiation and can be regulated by the serine-threonine kinase Pim-1. Overexpressed versions of c-Myb and Pim-1 are believed to play a key role in the development of a wide variety of leukemias and tumors. In our study, we evaluated the effects of benzene and the metabolites catechol and phenol on c-Myb signaling to investigate our hypothesis that benzene exerts its toxicity by interfering with this pathway. To evaluate this hypothesis, HD3 chicken erythroblast cells were transiently transfected with a c-Myb responsive luciferase reporter plasmid and then exposed to benzene, catechol, or phenol (0-300 microM) for 1-24 h before nonproprietary dual luciferase activities were measured. Our results demonstrated that catechol exposure caused a time- and concentration-dependent increase in c-Myb activity with significance occurring at 100 and 300 microM after 24 h of exposure, which was independent of increased Pim-1 protein, but dependent on increased c-Myb phosphorylation. Benzene and phenol exposure resulted in small but significant decreases in c-Myb activity that were not dose- and time-dependent, nor was increased Pim-1 protein involved. These results are consistent with other studies, which suggest metabolite differences in benzene-mediated toxicity. More importantly, this study supports the hypothesis that benzene may mediate its toxicity through metabolite-mediated alterations in the c-Myb signaling pathway.

Animals↗
PubMed1998

Catechol estrogens as inhibitors of leukotriene synthesis.

Estrogens have a beneficial effect on atherosclerosis and osteoporosis after menopause, but their exact mechanism of action is still unknown. The aim of the present study was to investigate the effects of estradiol and its metabolites catechol estrogens on arachidonic acid metabolism in vitro. Estradiol had no effect on arachidonic acid metabolism up to 33 microM in A23187-stimulated human whole blood. All catechol estrogens (2-hydroxyestradiol, 2-hydroxyestrone, 4-hydroxyestradiol and 4-hydroxyestrone) had similar kinds of actions on arachidonic acid metabolism, being over ten times more potent inhibitors of leukotriene synthesis (IC50 values 0.044-0.16 microM) than thromboxane (IC50 values 0.99-2.1 microM) and prostaglandin E2 synthesis (IC50 values 0.84-5.5 microM). It is suggested that some of the protective actions of estrogens--e.g., on atherosclerosis and osteoporosis--may be related to the inhibition of leukotriene synthesis by catechol estrogens.

Arachidonate 5-Lipoxygenase↗
PubMed1985

Evidence that covalent binding of metabolically activated phenol to microsomal proteins is caused by oxidised products of hydroquinone and catechol.

The metabolic activation of [14C]phenol resulting in covalent binding to proteins has been studied in rat liver microsomes. The covalent binding was dependent on microsomal enzymes and NADPH and showed saturation kinetics for phenol with a Km-value of 0.04 mM. The metabolites hydroquinone and catechol were formed at rates which were 10 or 0.7 times that of the binding rate of metabolically activated phenol. The effects of cytochrome P-450 inhibitors and cytochrome P-450 inducers on the metabolism and binding of phenol to microsomal proteins, suggest that cytochrome P-450 isoenzyme(s) other than P-450 PB-B or P-450 beta NF-B catalyses the metabolic activation of phenol. Furthermore, reconstituted mixed-function oxidase systems containing cytochrome P-450 PB-B and P-450 beta NF-B were (on basis of cytochrome P-450 content) 6 and 11 times less active in catalysing the formation of hydroquinone than microsomes. The isolated metabolites hydroquinone and catechol bound more extensively to microsomal proteins than phenol and the binding of these was not stimulated by NADPH. The binding occurring during the metabolism of phenol could be predicted by the rates of formation of hydroquinone and catechol and the rates by which the isolated metabolites were bound to proteins.

Animals↗
PubMed2002

A synthesis of the phenolic lipid, 3-[(Z)-pentadec-8-enyl] catechol, (15:1)-urushiol.

A synthesis of (15:1)-urushiol, urushiol monoene, 3-[(Z)-pentadec-8-enyl] catechol, 1,2-dihydroxy-3-[(Z)-pentadec-8-enyl] benzene, one of the toxic principles of Rhus toxicodendron and of Rhus vernicifera is described. 6-Chlorohexan-1-ol protected at the OH group with ethyl vinyl ether reacted with 2,3-dimethoxybenzaldehyde in the presence of lithium to give, after removal of the protective group with methanolic 4-toluenesulphonic acid, 1-(2,3-dimethoxyphenyl) heptane-1,7-diol. Catalytic hydrogenolysis in ethanol with palladium-carbon selectively afforded 7-(2,3-dimethoxyphenyl)heptane-1-ol accompanied by a small proportion of the 7-(3-methoxyphenyl)heptane-1-diol, formed by demethoxylation. Reaction of the dimethoxy compound with boron tribromide resulted in both bromination and demethylation to give 7-(2,3-dihydroxyphenyl) heptylbromide. This bromide in tetrahydrofuran (THF) containing hexamethylphosphoric triamide reacted with excess lithium oct-1-yne to give 3-(pentadec-8-enyl)catechol which, by catalytic hydrogenation in ethyl acetate containing quinoline, selectively formed the required cis product, 3-[(Z)-pentadec-8-enyl]catechol which was identical chromatographically and spectroscopically with urushiol monoene separated from the natural product.

Catechols↗
PubMed2003

Simultaneous determination of 5-hydroxyindoles and catechols by high-performance liquid chromatography with fluorescence detection following derivatization with benzylamine and 1,2-diphenylethylenediamine.

A highly selective and sensitive method for the simultaneous determination of 5-hydroxyindoles and catechols (serotonin, norepinephrine, dopamine and related compounds) by high-performance liquid chromatography with fluorescence detection is described. The method is based on the two-step precolumn derivatization of 5-hydroxyindoles and catechols with benzylamine (BA) and 1,2-diphenylethylenediamine (DPE), respectively, resulting in highly fluorescent and stable benzoxazole derivatives. The first derivatization with BA proceeds at room temperature (ca. 23 degrees C) for 2 min in a mixture of 0.3 M 3-cyclohexylamino-1-propanesulfonic acid buffer (pH 10.0) and methanol in the presence of potassium hexacyanoferrate(III). The subsequent second derivatization with DPE is carried out at 50 degrees C for 20 min in the presence of glycine. The resulting fluorescent derivatives of five 5-hydroxyindoles and seven catechols are separated on a reversed-phase column (150 x 1.5 mm I.D., packed with C18 silica, 5 microm) with isocratic elution using a mixture of acetonitrile-15 mM acetate buffer (pH 4.5) (34:66, v/v) containing 1 mM octanesulfonic acid sodium salt, and are detected spectrofluorimetrically at 480 nm with excitation at 345 nm. The detection limits (signal-to-noise ratio of 3) of the related compounds are 80 amol to 86 fmol for a 20-microl injection.

Benzylamines↗
PubMed2002

Adduction of catechol estrogens to nucleosides.

We report the formation, detection, quantitation and structural characterization of products resulting from the adduction of deoxynucleosides (deoxyadenosine, deoxyguanosine, deoxycytidine and 5-methyldeoxycytidine) to the catechol estrogens (CE) of estrone, estradiol-17beta and estradiol-17 alpha. The crude products are obtained in a one-pot synthesis through oxidation of catechols to quinones and subsequent Michael-type reaction with the deoxynucleosides in acidic medium. In all experiments, adducts are detected by electrospray ionization mass spectrometry analysis after HPLC separation (LC/ESI/MS(n)). The two pyrimidines deoxycytidine and 5-methyldeoxycytidine yield only CE adducts to deoxynucleosides, which correspond to stable adducts on DNA. For purines, the results depend on the CE (2,3- or 3,4-catechols) used, the function and configuration on carbon 17 (ketone for estrone, alcohol for alpha and beta isomers of estradiol), and on the purine itself (deoxyadenosine or deoxyguanosine). Both stable adducts and deglycosylated adducts are formed, and therefore formation of stable adducts on DNA as well as the loss of purines from the DNA strands could be possible. MS(2) and MS(3) experiments prove to be relevant for further structural determinations, enabling in some cases the elucidation of the regiochemistry of adduction on the A and B rings of the steroid moiety.

Chromatography, High Pressure Liquid↗
PubMed1999

Determination of differential activities of soluble and membrane-bound catechol-O-methyltransferase in tissues and erythrocytes.

Catechol-O-methyltransferase (COMT) exists as two isoenzymes, a membrane-bound form (MB-COMT) and a soluble form (S-COMT), with different roles in the metabolism of catecholamines and other catechol compounds. This report documents an HPLC assay for separate estimation of S-COMT and MB-COMT activity and examines activities of the two isoenzymes among different rat tissues and in human and rat erythrocytes. Activities of MB-COMT and S-COMT varied widely among tissues. There were higher activities of S-COMT than MB-COMT in all tissues except the adrenal medulla where MB-COMT was the predominant isoenzyme, consistent with the importance of this tissue and MB-COMT for the O-methylation of catecholamines. MB-COMT and S-COMT in rat and human erythrocytes showed divergent levels and patterns of activity. The assay represents a rapid and accurate method for quantifying MB-COMT and S-COMT in various tissues and examining the relative roles of COMT isoenzymes in the metabolism of catechol compounds in health and disease.

Animals↗
PubMed2001

A new sensitive and selective spectrophotometric method for the determination of catechol derivatives and its pharmaceutical preparations.

A sensitive and simple spectrophotometric method for the estimation of certain catechol derivatives like pyrocatechol (PCL), dopamine hydrochloride (DPH), levodopa (LDP), methyl dopa (MDP) and adrenaline (ADH) in either pure form or in its pharmaceutical formulation is described. The method is based on the interaction of diazotised p-nitro aniline (DPNA) with catechol derivatives in presence of molybdate ions in acidic medium. Absorbance of the resulting red complex is measured at 500-510 nm, respectively, and is stable for 2-10 h. The method is highly reproducible and specific for these selected catechol derivatives. The common excipients used as additives in pharmaceuticals and phenol, hydroquinone, resorcinol, pyrogallol and phloroglucinol do not interfere in the proposed method. Analytical data for determination of the pure compound is presented together with the application of the proposed method to the analysis of some pharmaceutical formulations. The results compare favourably with those of official and reported methods.

Catechols↗
PubMed2003

Catechols from abietic acid synthesis and evaluation as bioactive compounds.

Catechols from abietic acid were prepared by a short and good yielding chemical process and further evaluated for several biological activities namely, antifungal, antitumoral, antimutagenic, antiviral, antiproliferative and inhibition of nitric oxide. Their properties were compared with those of carnosic acid (6), a naturally occurring catechol with an abietane skeleton and known to possess potent antioxidant activity, as well as anticancer and antiviral properties. From all the synthetic catechols tested compound 2 showed the best activities, stronger than carnosic acid.

Abietanes↗
PubMed2005

Influence of chemical kinetics on postcolumn reaction in a capillary Taylor reactor with catechol analytes and photoluminescence following electron transfer.

Postcolumn derivatization reactions can enhance detector sensitivity and selectivity, but their successful combination with capillary liquid chromatography has been limited because of the small peak volumes in capillary chromatography. A capillary Taylor reactor (CTR), developed in our laboratory, provides simple and effective mixing and reaction in a 25-microm-radius postcolumn capillary. Homogenization of reactant streams occurs by radial diffusion, and a chemical reaction follows. Three characteristic times for a given reaction process can be predicted using simple physical and chemical parameters. Two of these times are the homogenization time, which governs how long it takes the molecules in the analyte and reagent streams to mix, and the reaction time, which governs how long the molecules in a homogeneous solution take to react. The third characteristic time is an adjustment to the reaction time called the start time, which represents an estimate of the average time the analyte stream spends without exposure to reagent. In this study, laser-induced fluorescence monitored the extent of the postcolumn reaction (reduction of Os(bpy)3(3+) by analyte to the photoluminescent Os(bpy)3(2+)) in a CTR. The reaction time depends on the reaction rates. Analysis of product versus time data yielded second-order reaction rate constants between the PFET reagent, tris(2,2'-bipyridine)osmium, and standards ((ferrocenylmethyl)trimethylammonium cation and p-hydroquinone) or catechols (dopamine, epinephrine, norepinephrine, 3, 4-dihydroxyphenylacetic acid. The extent of the reactions in a CTR were then predicted from initial reaction conditions and compared to experimental results. Both the theory and experimental results suggested the reactions of catechols were generally kinetically controlled, while those of the standards were controlled by mixing time (1-2 s). Thus, the extent of homogenization can be monitored in a CTR using the relatively fast reaction of the reagent and p-hydroquinone. Kinetically controlled reactions of catechols, however, could be also completed in a reasonable time at increased reagent concentration. A satisfactory reactor, operating at 1.7 cm/s (2 microL/min) velocity with solutes having diffusion coefficients in the 5 x 10(-6) cm2/s range, can be constructed from 8.0 cm of 25-microm-radius capillary. Slower reactions require longer reaction times, but theoretical calculations expect that a CTR does not broaden a chromatographic peak (N = 14 000) from a 100-microm-capillary chromatography column by 10% if the pseudo-first-order rate constant is larger than 0.1 s(-1).

Catechols↗
PubMed1995

Structure and kinetics of formation of catechol complexes of ferric soybean lipoxygenase-1.

Ferric soybean lipoxygenase forms stable complexes with 4-substituted catechols. The structure of the complex between the enzyme and 3,4-dihydroxybenzonitrile has been studied by resonance Raman, electron paramagnetic resonance, visible, and X-ray spectroscopies. It is a bidentate iron-catecholate complex with at least one water ligand. The kinetics of formation of complexes between lipoxygenase and 3,4-dihydroxybenzonitrile and 3,4-dihydroxyacetophenone have been studied by stopped-flow spectroscopy. The data are consistent with two kinetically distinct, reversible steps. The pH dependence of the first step suggests that the substrate for the reaction is the catechol monoanion. When these results are combined, plausible mechanisms for the complexation reaction are suggested.

Catechols↗
PubMed1988

Activation and irreversible binding of regiospecifically labeled catechol estrogen by rat liver microsomes: evidence for differential cytochrome P-450 catalyzed oxidations.

Estradiol and 2-hydroxyestradiol labeled with 3H at different positions in rings A or B were incubated with male rat liver microsomes, and their oxidative transformation was followed by the transfer of 3H into 3H2O. 14C-labeled estrogen or catechol estrogen was used to determine the fraction that becomes bound covalently to microsomal protein. The further metabolism of 2-hydroxyestradiol involves activation of the steroid at C-4 and, to a much lesser extent at C-1, by a cytochrome P-450 mediated reaction as indicated by the effects of NADPH, spermine, SKF-525A, and CO in the microsomal system. Glutathione promoted the loss of 3H from C-4 of either estradiol or 2-hydroxyestradiol but had less effect on this reaction at C-1 and inhibited it at C-6,7. It also abolished the irreversible binding of 14C-labeled estradiol and 2-hydroxyestradiol to microsomal protein. NADPH was needed specifically for glutathione to exert its effect both on the transfer of 3H into 3H2O and on the formation of water-soluble products from catechol estrogen by rat liver microsomes. It could not be replaced by NADP, NAD, or NADH. Ascorbic acid inhibited these enzymatic reactions but did not affect significantly the initial 2-hydroxylation of estradiol. Evidence is also provided for the further hydroxylation of 2-hydroxyestradiol at C-6 (or C-7). These results indicate that cytochrome P-450 activates catechol estrogens by an electron abstraction process.

Animals↗
PubMed1989

Characterization of free radicals produced during oxidation of etoposide (VP-16) and its catechol and quinone derivatives. An ESR Study.

Spectroscopic evidence for the radical-mediated metabolism of VP-16, VP-16 catechol, and VP-16 quinone during enzymatic oxidation and autoxidation has been obtained. Autoxidation of the catechol yields the primary semiquinone together with the primary molecular product VP-16 quinone, which subsequently undergoes hydrolytic oxidation to form secondary quinones and semiquinones. Both primary and secondary phenoxyl radicals were detected during peroxidatic oxidation of VP-16. Neither the primary nor the secondary radicals react with DNA at a detectable rate. Evidence for the production of hydroxyl radical during iron-catalyzed oxidation of VP-16 catechol was obtained. These free radical reactions may have implications for the mechanism of antitumor action of VP-16.

Catechols↗
PubMed2003

Phenol and catechol biodegradation by the haloalkaliphile Halomonas campisalis: influence of pH and salinity.

Removal of aromatic compounds from alkaline and/or saline industrial wastewater is an environmental concern for industry. In addition, aromatics may be accumulating in soda lakes, unique natural systems, where the fate and toxicity of these contaminants is unknown. To determine the feasibility of aromatic compound biodegradation in saline and alkaline conditions, the effect of pH and salinity on the biodegradation of phenol as a model aromatic waste compound by the haloalkaliphilic bacterium Halomonas campisalis was examined. Phenol was degraded as a source of carbon and energy at pH 8-11 and 0-150 g/L NaCl. Metabolic intermediates catechol, cis,cis-muconate, and (+)-muconolactone were identified, thus indicating that phenol was degraded via the beta-ketoadipate metabolic pathway. Although phenol and catechol were completely degraded in all cases, small amounts of cis,cis-muconate accumulated proportionally to increases in pH. There was no noticeable influence of salinity on cis,cis-muconate accumulation except at 0 g/L NaCl where it was completely degraded. These results indicate that it may be feasible to use haloalkaliphiles forthe treatment of aromatics present in saline and/or alkaline systems. This is the first report of phenol and catechol biodegradation under combined saline and alkaline conditions.

Biodegradation, Environmental↗