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PubMed1987

Kinetics and inhibition studies of catechol O-methyltransferase from the yeast Candida tropicalis.

The Kms for esculetin and S-adenosyl-L-methionine for catechol O-methyltransferase from the yeast Candida tropicalis were 6.2 and 40 microM, respectively. S-Adenosyl-L-homocysteine was a very potent competitive inhibitor with respect to S-adenosyl-L-methionine, with a Ki of 6.9 microM. Of the catechol-related inhibitors, purpurogallin, with a Ki of 0.07 microM, showed the greatest inhibitory effect. Sulfhydryl group-blocking reagents, such as thiol-oxidizing 2-iodosobenzoic acid and mercaptide-forming p-chloromercuribenzoic acid, provided evidence for sulfhydryl groups in the active site of the enzyme. Yeast catechol O-methyltransferase is a metal-dependent enzyme and requires Mg2+ for full activity. Zn2+ and Mn2+ but not Ca2+ were able to substitute for Mg2+. Mn2+ showed optimal enzyme activation at concentrations 50- to 100-fold lower than those of Mg2+.

Benzocycloheptenes↗
PubMed1981

Streptomyces setonii: catabolism of vanillic acid via guaiacol and catechol.

Streptomyces setonii (strain 75Vi2) was grown at 45 degrees C in liquid media containing simple aromatic compounds as principal carbon sources. Thin-layer chromatography, UV spectrophotometry, and gas chromatography were used to show that S. setonii converted benzoic acid, guaiacol, and vanillic acid to catechol; p-hydroxybenzoic acid to protocatechuic acid; and m-hydroxybenzoic acid to gentisic acid. Presence of the ring-cleavage enzymes catechol 1,2-dioxygenase, protocatechuate 3,4-dioxygenase, and gentisate 2,3-dioxygenase was shown both by O2 uptake in ring-cleavage reactions catalyzed by cell-free extracts and by changes in UV spectra that indicated the presence of specific ring-cleavage products. A unique feature of this strain was its catabolism of vanillic acid by of guaiacol and catechol, using a pathway that had not been confirmed previously.

Benzoates↗
PubMed1999

Capillary electrophoresis of monoamines and catechol with indirect chemiluminescence detection.

A capillary electrophoresis (CE)/indirect chemiluminescence (CL) detection method is described for monoamines, viz., serotonin (5-HT), dopamine (DA), epinephrine (EP), and norepinephrine (NE) and for catechol (CA). Optimal separation and detection were obtained with an electrophoretic buffer of 10 mM sodium borate (pH 9.5) containing 5 mM luminol and 25 mM H2O2, and a catalyst solution of 30 microM CuSO4 in 30 mM borate buffer (pH 10.0). Complete separation of 5-HT, DA, EP, NE and CA was achieved in less than 5 min. The Cu(II)-catalyzed luminol CL reaction was employed to provide the high and constant background. Since monoamines and catechol can form stable complexes with Cu(II), inverted analyte peaks due to decreased catalytic activity of Cu(II) can be detected. The degree of CL suppression is proportional to the analyte concentrations. Linearity (r> or =20.99) over two orders of magnitude was generally obtained. The concentration limits of detection (CLODs) for the monoamines and catechol studied were between 0.5 and 3.1 uM. The relative standard deviation (RSD) values on peak size and migration time were in the ranges 3.2-4.4% and 0.4-0.5%, respectively. The applicability of the method for the analysis of pharmaceutical and biological samples was examined.

Calibration↗
PubMed2006

The effect of temperature on the analysis of metanephrine for catechol-O-methyltransferase activity assay by HPLC with electrochemical detection.

The enzyme catechol-O-methyltransferase (COMT) plays an important role in the metabolism of catechol estrogens and degradation of the catecholamine neurotransmitters, such as epinephrine. Several analytical methods, mainly high-performance liquid chromatography with electrochemical amperometric detection, have been reported for the analysis of catecholamines and their metabolites in biological fluids. In this paper we report the relevance of controlling temperature in calibration procedures of metanephrine, an O-methylated product of catechol-O-methyltransferase, using epinephrine as substrate. The results at higher temperatures show shorter retention times of metanephrine, no undue band-broadening and increased electro signals. This study also showed that, despite different temperatures leading to similarly specific activities of recombinant human COMT as expected, there are additional advantages in flow analytical methods where good sensitivity, efficiency and selectivity is required, mainly in tissues with low levels of COMT activity.

Catechol O-Methyltransferase↗
PubMed1988

A gas chromatographic/mass spectrometric assay for catechol estrogens in microsomal incubations: comparison with a radiometric assay.

A gas chromatographic/mass spectrometric assay for quantifying two catechol estrogens, 2-hydroxyestradiol and 4-hydroxyestradiol, in microsomal preparations is described. The assay employs deuterium-labeled analogs of the catechol estrogens as internal standards and permits quantification of catechol estrogens, in microsomal incubations, at low (1-2) microM concentrations. The compounds are analyzed as their trimethylsilyl derivatives following separation by capillary gas chromatography.

Animals↗
PubMed2003

Density functional characterization of the chemoselective oxidation of catechol by using molecular oxygen: thermodynamics of the reaction between [(triphos)Ir(dtbc)]+ and O2.

The catalytic mechanism of intra and extra catechol cleaving dioxygenases is still a matter of debate, because the intermediate transient oxygen adduct has never been isolated in these enzymes. The complex [(triphos)Ir(dtbc)](+) (triphos=MeC(CH(2)PPh(2))(3), DBTC(2-)=3,5-di-tert-butylcatecholate), reacts with molecular oxygen and exhibits a ring-cleaving catalytic activity, and a stable oxygen intermediate appears; this stimulates an opportunity for obtaining information that can be transferable to the above-mentioned enzymatic catalytic centers, therefore, giving a breakthrough into the strategy of oxygen activation in these natural systems. Here, we present the results of our computational approach, based on density functional theory, focusing on the following aspects: to explain the interaction with molecular oxygen and how to avoid the existing spin problem, to understand the formation of the bridging moiety, to clarify, if any, the possible influence on the structure of the formed adduct of the bidentate versus monodentate binding of the catechol ligand, and to disclose, eventually, the nature of final decomposition products with the aim to rationalize the intra versus extra cleavage of the catechol molecule itself.

Catechols↗
PubMed2004

A critical evaluation of the factors determining the effect of intramolecular hydrogen bonding on the O-H bond dissociation enthalpy of catechol and of flavonoid antioxidants.

New experimental results on the determination of the bond dissociation enthalpy (BDE) value of 3,5-di-tert-butylcatechol, a model compound for flavonoid antioxidants, by the EPR radical equilibration technique are reported. By measurement of the equilibrium constant for the reaction between 3,5-di-tert-butylcatechol and the 2,6-di-tert-butyl-4-methylphenoxyl radical, in UV irradiated isooctane solutions at different temperatures, it has been shown that the thermodynamic parameters for this reaction are DeltaH degrees = -2.8+/-0.1 kcal mol(-1) and DeltaS degrees = +1.3+/-0.2 cal mol(-1) K(-1). This demonstrates that the entropic variations in the hydrogen exchange reaction between phenols and the corresponding phenoxyl radicals are also negligible when one of the reacting species is a polyphenol and that the EPR radical equilibration technique also allows the determination of the Obond;H BDEs in intramolecularly hydrogen-bonded polyphenols. The BDE of 3,5-di-tert-butylcatechol (78.2 kcal mol(-1)) was determined to be identical to that of alpha-tocopherol. Through use of the group additivity rule, this piece of data was also used to calculate the strength of the intramolecular hydrogen bond between the hydroxyl proton and the oxygen radical centre in the corresponding semiquinone radical (5.6 kcal mol(-1)), which is responsible both for the excellent antioxidant properties of catechols and for the BDE of catechol (81.8 kcal mol(-1)). These values are in poor agreement with those predicted by DFT calculations reported in the literature (9.5 kcal mol(-1) and 77.6 kcal mol(-1), respectively). Extensive theoretical calculations indicate that the BDE of catechol is reproduced well (81.6 kcal mol(-1)) by use of diffuse functions on oxygen and the CCSD method.

Antioxidants↗
PubMed1983

Inhibition of dihydropteridine reductase by catechol estrogens.

Catechol estrogens, such as 2-hydroxyestriol, 2-hydroxyestradiol, and 2-hydroxyestrone, inhibit human liver dihydropteridine reductase noncompetitively with Ki values ranging from 1.5 to 4.6 X 10(-6)M. Catechol estrogens lose approximately half of their inhibitory potency if the C-2 hydroxyl groups are methylated. Thus, 2-methoxyestrogens have inhibitory potencies equivalent to those of their parent estrogens--estriol, estradiol, and estrone. Aromatization of ring B or stereoisomerism at C-17 does not affect the inhibitory potency of estrogens, although stereoisomerism at C-16 enhances the inhibitory potency of estriol. These results support the hypothesis that catechol estrogens may interfere with catecholamine metabolism by acting as inhibitors of enzymes involved in catecholamine metabolism, such as dihydropteridine reductase.

Dihydropteridine Reductase↗
PubMed1988

Charge transfer complexes of indole:catechol type II.

Charge transfer complexes between tryptamine:epinephrine, tryptamine:isoproterenol, tryptamine:catechol, and indole:catechol were demonstrated spectrophotometrically in aqueous solutions containing 0.1 M HCl. It was possible to make precise measurements and to calculate thermodynamic parameters and molar absorptivities. In general, the equilibrium constant was found to be quite low and ranged from 4.00 +/- 0.04 to 0.30 +/- 0.02 M-1. These interactions are exothermic and have relatively large standard enthalpy and entropy changes (delta Ho values ranged from -7.4 +/- 0.3 to -5.2 +/- 0.4 kcal mol-1; delta So ranged from -25 +/- 5.0 to -16 +/- 1.3 cal K-1 mol-1). The similarity in delta Ho and delta So values for all the combinations indicates a similar interacting system. This result has led us to propose the involvement of the charge transfer effect, induced in the indole:catechol system, in the mechanism occurring in nerve conductions.

Catechols↗
PubMed1996

Characterization of the gene encoding catechol 2,3-dioxygenase of Alcaligenes sp. KF711: overexpression, enzyme purification, and nucleotide sequencing.

Catechol 2,3-dioxygenase (C23O) is an extradiol-type dioxygenase that catalyzes the aromatic ring fission of catechol to form 2-hydroxymuconic semialdehyde. The C23O gene of Alcaligenes sp. KF711 was overexpressed in Escherichia coli HB101 by using the lac promoter of pUC18, and its gene product was purified by using immunoaffinity chromatography. The purified C23O exhibited a 35-kDa single band on an SDS-polyacrylamide gel, and its ring-fission activity on dihydroxylated aromatics was 4-methylcatechol > 4-chlorocatechol > catechol > 3-methylcatechol >> 2,3-dihydroxybiphenyl. Nucleotide sequence analysis of the C23O gene revealed an open reading frame of 927 bp, which can encode a polypeptide of 308 amino acid residues. The predicted molecular mass of 35 kDa is in agreement with that of purified C23O on an SDS-polyacrylamide gel. The amino acid sequence of the C23O was compared with those of nine other extradiol-type dioxygenases, including 2,3-dihydroxybiphenyl dioxygenase (2,3-DHBD) and 1,2-dihydroxynaphthalene dioxygenase (1,2-DHND). The C23O of Alcaligenes sp. KF711 exhibited 80 to 94% identity in amino acid sequence with other C23Os, and 20 to 25% identity with 1,2-DHND and 2,3-DHBDs. Furthermore, sequence comparison of 10 extradiol-type dioxygenases has led to identifying 19 evolutionarily conserved amino acid residues whose possible catalytic roles are proposed.

Alcaligenes↗
PubMed1996

Structure of catechol 2,3-dioxygenase gene encoded in chromosomal DNA of Pseudomonas putida KF715.

A catechol 2,3-dioxygenase gene in chromosomal DNA of P. putida KF715 was cloned and its nucleotide sequence analyzed. The enzyme gene was composed of 924 base pairs with ATG initiation codon and TGA termination codon, which can encode a polypeptide of molecular weight 35 kDa containing 307 amino acids. A promoter-like sequence and a ribosome-binding sequence were identified upstream the enzyme gene. A deduced amino acid sequence of the catechol 2,3-dioxygenase exhibited 94% identity with that of corresponding enzyme in TOL plasmid and 25% identity with that of 2,3-dihydroxybiphenyl 1,2-dioxygenase from the same strain. Furthermore, sequence comparison of the catechol 2,3-dioxygenase with other extradiol-type dioxygenases has led to identify evolutionally conserved amino acid residues whose possible catalytic roles are proposed.

Amino Acid Sequence↗
PubMed2000

Catechol concentrations in the hemolymph of the scallop, Placopecten magellanicus.

Catecholamines have previously been detected in numerous tissues and are thought to control a wide variety of physiological functions in bivalve molluscs. In the present study, alumina extraction and high-performance liquid chromatography reveal the presence of significant concentrations of 3,4-dihydroxyphenylalanine (DOPA), dopamine, and 3,4-dihydroxyphenylacetic acid (DOPAC) in the hemolymph of the sea scallop, Placopecten magellanicus. The concentration of dopamine in the hemolymph averaged 223.8 ng/ml, (+/-48.4, SEM), equivalent to 10(-7) to 10(-6) M. Neither epinephrine nor norepinephrine was reliably detected in significant quantities. Previous studies have demonstrated physiological responses to dopamine with thresholds of 10(-9) to 10(-6) M, thus suggesting that this catecholamine may have an endocrine function. Furthermore, monitoring hemolymph concentrations of catechols might provide a sensitive measure of the physiological status of bivalves. For example, drugs known to affect catechol concentrations in other tissues also effect hemolymph levels. Administration of monoamine oxidase inhibitors such as pargyline, deprenyl, and clorgyline at 10(-4) M for 1 day of incubation followed by a 2-day wash resulted in decreased hemolymph concentrations of DOPAC and increased concentrations of its precursors, DOPA and dopamine. Incubation in 10(-4) M 3,5-dinitrocatechol, a catecholamine-O-methyl transferase blocker, for 1 day followed by a 2-day wash significantly increased the concentration of dopamine and DOPAC in the hemolymph. Scallops incubated in 10(-5) M alpha-methyl-p-tyrosine, a blocker of tyrosine hydroxylase, for 1 day followed by a 3-day wash in artificial seawater had significantly reduced concentrations of DOPA, dopamine, and DOPAC in the hemolymph. In addition to responding to pharmacological agents, dopamine levels also decreased significantly following thermal induction of spawning, thus suggesting that hemolymph concentrations of catechols might provide indices of reproductive activity and/or stress.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1988

Effects of the facilitatory compounds catechol, guanidine, noradrenaline and phencyclidine on presynaptic currents of mouse motor nerve terminals.

Catechol, guanidine, noradrenaline, and phencyclidine can increase acetylcholine release at neuromuscular junctions. To determine if they act by affecting nerve terminal action potentials, the electrical activity of the terminal regions of motor nerves was recorded with an extracellular electrode inserted in the perineural sheaths of nerves in the mouse triangularis sterni preparation. Catechol (from 10 microM) and guanidine (from 1 mM) produced a selective reduction in the component of the perineural waveform associated with voltage-dependent K+ currents, without significant effects on Na+, Ca2+, or Ca2+-activated K+ currents. A selective block of K+ channels in nerve terminals would cause a prolonged depolarization and hence a large influx of Ca2+ to trigger acetylcholine release; this could explain the facilitatory effects of guanidine and catechol. Noradrenaline produced a slight increase in the amplitude of the perineural waveform. This is consistent with hyperpolarization of the resting membrane potential of the nerve, which could lead to facilitation of acetylcholine release. Phencyclidine blocked Na+- and K+-related portions of the signal.

Animals↗
PubMed1986

Direct inhibition of tyrosine hydroxylase from PC-12 cells by catechol derivatives.

Several drugs with a catechol moiety were studied for their potency to inhibit tyrosine hydroxylase (TH) from PC-12 cells in vitro. When the natural compounds tested were compared, dopamine, norepinephrine and 2(3,4-dihydroxyphenyl)-ethanol (DOPET) were most effective (IC50 between 1.4 and 3.6 microM with 0.5 microM 6(R,S)-L-erythro-5,6,7,8-tetrahydrobiopterin as cofactor). 3,4-Dihydroxyphenylalanine (DOPA; IC50: 35 microM) and 3,4-dihydroxyphenylacetic acid (DOPAC; IC50: 180 microM were less potent inhibitors. Among the synthetic drugs possessing catechol moiety, isoproterenol, (+/-)-2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (6,7-ADTN) and (+/-)-2-dimethylamino-6,7-dihydroxy-tetrahydronaphthalene (TL-99) had the same inhibitory effects as the natural catecholamines (IC50 between 1.6 and 3.9 microM), whereas the apomorphine derivatives and 2,3,4,5-tetrahydro-1-phenyl-1 H-3-benzazepine-7,8-diol (SKF 38393) were even more potent (IC50: 0.5-0.8 microM). These results demonstrate that natural catechols and certain drugs (e.g. 6,7-ADTN, TL-99, SKF 38393) are more effective direct blockers of tyrosine hydroxylase than generally assumed provided appropriate assay conditions are used. In the case of dopamine and norepinephrine, these findings suggest a reevaluation of their role for feedback control of tyrosine hydroxylase in vivo.

Adrenal Gland Neoplasms↗
PubMed1988

Limitations of the quantitative cytochemical assay of catechol oxidase in melanoma cells.

The cytochemical quantification of catechol oxidase activity in fixed B16 melanoma cells was investigated using dopa as the substrate. Inhibitors showed that peroxidases do not significantly interfere. The kinetics of melanin formation were studied initially in solution with purified catechol oxidase. Two key parameters were identified: lag-time and the rate of melanin formation. The lag-time was taken as the time required by intermediates to reach a critical concentration at which the polymerization process starts and melanin production becomes measurable (at 640 nm). In solution, the lag-time decreases as the enzyme activity increases, particularly when the activity is very low. The rate at which melanin is formed by pure enzyme in solution is independent of dopa concentration when its activity is low but increases linearly with dopa concentration when the activity is comparatively high. In fixed melanoma cells, the lag-time decreases linearly with increases of dopa concentrations up to 20 mM; at concentrations higher than this, the lag decreases more slowly. In contrast, the rate of melanin production is unaffected by changes in dopa concentration. The lag-times of different cells lines incubated at the same substrate concentration decrease as the enzyme activity of the cells increases. The rate of melanin production seems to be affected by factors other than catechol oxidase activity, such as the intracellular organization and distribution of the enzyme.

Catechol Oxidase↗
PubMed2002

Initiation of cancer and other diseases by catechol ortho-quinones: a unifying mechanism.

Exposure to estrogens is a risk factor for breast and other human cancers. Initiation of breast, prostate and other cancers has been hypothesized to result from reaction of specific estrogen metabolites, catechol estrogen-3,4-quinones, with DNA to form depurinating adducts at the N-7 of guanine and N-3 of adenine by 1,4-Michael addition. The catechol of the carcinogenic synthetic estrogen hexestrol, a hydrogenated derivative of diethylstilbestrol, is metabolized to its quinone, which reacts with DNA to form depurinating adducts at the N-7 of guanine and N-3 of adenine. The catecholamine dopamine and the metabolite catechol (1,2-dihydroxybenzene) of the leukemogen benzene can also be oxidized to their quinones, which react with DNA to form predominantly analogous depurinating adducts. Apurinic sites formed by depurinating adducts are converted into tumor-initiating mutations by error-prone repair. These mutations could initiate cancer by estrogens and benzene, and Parkinson's disease by the neurotransmitter dopamine. These data suggest a unifying molecular mechanism of initiation for many cancers and neurodegenerative diseases and lay the groundwork for designing strategies to assess risk and prevent these diseases.

Animals↗
PubMed1999

Comparison of the downstream pathways for degradation of nitrobenzene by Pseudomonas pseudoalcaligenes JS45 (2-aminophenol pathway) and by Comamonas sp. JS765 (catechol pathway).

Nitrobenzene is degraded by Pseudomonas pseudoalcaligenes JS45 via 2-aminophenol to 2-aminomuconic semialdehyde, which is further degraded to pyruvate and acetaldehyde. Comamonas sp. JS765 degrades nitrobenzene via catechol to 2-hydroxymuconic semialdehyde. In this study we examined and compared the late steps of degradation of nitrobenzene by these two microorganisms in order to reveal the biochemical relationships of the two pathways and to provide insight for further investigation of their evolutionary history. Experiments showed that 2-hydroxymuconate, the product of the dehydrogenation of 2-hydroxymuconic semialdehyde, was degraded to pyruvate and acetaldehyde by crude extracts of Comamonas sp. JS765, which indicated the operation of a classical catechol meta-cleavage pathway. The semialdehyde dehydrogenases from Comamonas sp. JS765 and P. pseudoalcaligenes JS45 were able to metabolize both 2-amino- and 2-hydroxymuconic semialdehyde, with strong preference for the physiological substrate. 2-Aminomuconate was not a substrate for 4-oxalocrotonate decarboxylase from either bacterial strain. The close biochemical relationships among the classical catechol meta-cleavage pathway in Comamonas sp. JS765, 2-aminophenol meta-cleavage pathways in P. pseudoalcaligenes JS45, and an alternative 2-aminophenol meta-cleavage pathway in Pseudomonas sp. AP-3 suggest a common evolutionary origin.

Aminophenols↗
PubMed2003

A density functional investigation of the extradiol cleavage mechanism in non-heme iron catechol dioxygenases.

The mechanism for extradiol cleavage in non-heme iron catechol dioxygenase was modelled theoretically via density functional theory. Based on the Fe(II)-His,His,Glu motif observed in enzymes, an active site model complex, [Fe(acetate)(imidazole)(2)(catecholate)(O(2))](-), was optimized for states with six, four and two unpaired electrons (U6, U4 and U2, respectively). The transfer of the terminal atom of the coordinated dioxygen leading to "ferryl" Fe=O intermediates spontaneously generates an extradiol epoxide. The computed barriers range from 19 kcal mol(-1) on the U6 surface to approximately 25 kcal mol(-1) on the U4 surface, with overall reaction energies of +11.6, 6.3 and 7.1 kcal mol(-1) for U6, U4 and U2, respectively. The calculations for a protonated process reveal the terminal oxygen of O(2) to be the thermodynamically favoured site but subsequent oxygen transfer to the catechol has a barrier of approximately 30-40 kcal mol(-1), depending on the spin state. Instead, protonating the acetate group gives a slightly higher energy species but a subsequent barrier on the U4 surface of only 7 kcal mol(-1) relative to the hydroperoxide complex. The overall exoergicity increases to 13 kcal mol(-1). The favoured proton-assisted pathway does not involve significant radical character and has features reminiscent of a Criegee rearrangement which involves the participation of the aromatic ring pi-orbitals in the formation of the new carbon-oxygen bond. The subsequent collapse of the epoxide, attack by the coordinated hydroxide and final product formation proceeds with an overall exoergicity of approximately 75 kcal mol(-1) on the U4 surface.

Catechols↗