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PubMed1977

Catechol, a structural requirement for (Na+ + K+)-ATPase stimulation in rat skeletal muscle membrane.

1. Catecholamines can nearly double (Na+ + K+)-ATPase acts effect is not mediated by cyclic AMP and is not beta-adrenergic. 3. Orthodihydroxybenzene compounds and their orthoquinone derivatives enhance (Na+ + K+)-ATPase activity. 4. Enhancement of (Na+ + K+)-ATPase activity by catechols is not due to increased availability of ATP. 5. It is suggested that catechols and their orthoquinones somehow alter or protect the configuration of the enzyme so that it becomes more active or so protect the configuration of the enzyme so that it becomes more active or so that its activity is maintained under conditions in which its activity is otherwise diminished.

Adenosine Triphosphatases↗
PubMed1976

Evidence for sulfhydryl groups at the active site of catechol-O-methyltransferase.

Earlier studies using affinity labeling reagents have suggested the existence of two nucleophilic groups at the active site of catechol-O-methyltransferase (S-adenosyl-L-methionine:catechol O-methyltransferase, EC 2.1.1.6). Both nucleophilic residues are critical for catalytic activity. In an effort to elucidate the nature of these residues and to further characterize the relationship between the chemical structure and the catalytic function of this enzyme, inactivation studies using N-ethylmaleimide were undertaken. Inactivation of the enzyme by N-ethylmaleimide under pseudo first-order conditions exhibited a non-linear relationship between the log of the fraction of enzyme activity remaining and preincubation time. Kinetic analysis of this inactivation process suggested the modification by N-ethylmaleimide of two residues at the active site of the enzyme, both crucial for catalytic activity. Detailed analysis of the inactivation process including substrate protection studies, pH profiles of inactivation, and incorporation studies using N-ethyl[2,3-14C2]maleimide provided additional evidence to support this conclusion.

Binding Sites↗
PubMed1988

Covalent binding of catechols to proteins through the sulphydryl group.

The cytotoxicity of catechols has been ascribed to covalent binding of the o-quinone oxidation products to proteins through the sulphydryl group. We have previously shown that dopaquinone can bind covalently to proteins through cysteine residues to form protein-bound cysteinyldopas. In this study, we have compared the reactivities of o-quinones, derived from tyrosinase oxidation of various catechols, with the cysteine residue in bovine serum albumin. o-Quinone forms of dopamine, norepinephrine, N-acetyldopa, N-acetyldopamine, 3,4-dihydroxyphenylacetic acid, pyrocatechol and 4-methylcatechols were much more reactive than dopaquinone, while o-quinone forms of 5-S-cysteinyldopa and epinephrine were much less reactive. The yield of protein-bound cysteinylcatechols appears to depend on a competition between the intermolecular nucleophilic reaction of sulphydryl groups in protein and the intramolecular nucleophilic reaction of an amino group in the side chain.

Binding Sites↗
PubMed1979

Immunohistochemical demonstration of catechol-o-methyltransferase in mammalian brain.

Catechol-O-methyltransferase (COMT)(EC 2.1.1.6) was localized using fluorescence immunohistochemistry in rat liver and kidney and in rat, chinchilla, and bovine brains. In the brain, specific fluorescence was visable only in non-neuronal cellular elements in all three species. Ventricular ependymal cells and cells of the choroid plexuses exhibited the greatest intensity of immunofluorescence. Glial immunofluorescence appeared prominently in large myelinated fiber tracts. Interfascicular and perineuronal satellite oligodendrocytes as well as fibrous astrocytes were immunoreactive, though myelin itself did not exhibit a positive reaction. Bergmann glial cells in the cerebellum also stained brightly for COMT. Although this study indicates that the predominant localization of COMT is non-neuronal, it is important to note that the presence of small quantities of this enzyme in neurons cannot be excluded. The patterns of localization observed in the non-neuronal elements suggest that this enzyme may function as a barrier to free diffusion of catechol compounds within the central nervous system.

Animals↗
PubMed1981

Determination of free and conjugated catecholamines and L-3,4-dihydroxyphenylalanine in plasma and urine: evidence for a catechol-O-methyltransferase inhibitor in uraemia.

A sensitive, accurate and reproducible method has been developed for the determination of free and conjugated catecholamines and L-3,4-dihydroxyphenylalanine in plasma and urine. The assay involves the enzymatic conversion of these compounds to their radio-labelled O-methylated derivatives using catechol-O-methyltransferase and S-adenosyl-L-[methyl-(3)H]methionine. Recoveries of 75 + /- 5% for dopamine, 70 + /- 5% for adrenaline and 65 + /- 5% for noradrenaline were obtained. The sensitivities were 0.5 pg for adrenaline and noradrenaline and 5-7 pg for dopamine, and dihydroxyphenylalanine. Measurements of conjugated catecholamines were performed after mild acid hydrolysis for 20 min at 95 degrees C. During this procedure no degradation of the catecholamines was observed. This assay led to the discovery of a dialyzable factor in the plasma of chronic uraemic patients which inhibits catechol-O-methyltransferase activity in vitro. The mean 22% inhibition observed for unhydrolyzed plasma increased to 42% after hydrolysis. The identity of this inhibitor which exists as an inactive conjugated form, probably a sulphate ester, and its implication in physiopathological disorders remain to be established.

Adult↗
PubMed1991

Effect of clonidine on catechol metabolism in the rostral ventrolateral medulla: an in vivo electrochemical study.

The dose-dependent reduction in catechol metabolism induced by an imidazoline with alpha 2-adrenoceptor agonist specificity, clonidine, was assessed (ED50 = 7 micrograms.kg-1 i.v.) with in vivo voltammetry in the rostral ventrolateral medulla of rats kept under halothane anesthesia and strictly controlled circulatory and ventilatory conditions. This reduction in catechol metabolism was observed in intact as well as in barodeafferented rats.

Animals↗
PubMed1986

Aliphatic side chain of catecholamine potentiates the stimulatory effect of the catechol part on the synthesis of nerve growth factor.

Catecholamines are potent in stimulating nerve growth factor (NGF) synthesis in mouse L-M cells. The relationship between the structure of catecholamines and their stimulatory effect on NGF synthesis has been studied using various 3,4-dihydroxyphenyl derivatives or their analogues. All 3,4-dihydroxyphenyl derivatives with two saturated carbons on the side chain were potent stimulators, whereas those with only one carbon on the side chain were weak stimulators. Drugs lacking the catechol ring were not effective. These results suggest that the catechol part of catecholamines is essential for the stimulatory effect and that the aliphatic side chain potentiates this effect. The present results also suggest the terminal amino residue on the side chain is not critical for the effect.

Animals↗
PubMed1982

2-hydroxyethynyloestradiol as a substrate for catechol-O-methyltransferase--implications in the metabolism of ethynyloestradiol.

Highly purified pig catechol-O-methyltransferase catalyses the methylation of 2-hydroxyethynyloestradiol (KM - 11.0 microM, Vmax = 521.2 mU/mg protein, Vmax/KM = 47.4) more efficiently than that of 2-hydroxyoestradiol (KM = 68.5 microM, Vmax = 1056.2 mU/mg protein, Vmax/Km = 15.4), 2-hydroxyoestrone (KM = 38.0 microM, Vmax = 795.0 mU/mg protein, Vmax/KM = 20.9) or 4-hydroxyoestrone (KM = 12.8 microM, Vmax = 159.7, Vmax/KM = 12.5). This efficient methylation of the principal metabolite of ethynyloestradiol substantiates the implications of the studies of Bolt et al.[1] that O-methylation is a major route of ethynyloestradiol metabolism. Furthermore, this also implies that catechol-O-methyltransferase in involved in the protection, by S-adenoysylmethionine, against the impairment of bile secretion by ethynyloestradiol, observed in female rats [2].

Animals↗
PubMed1983

Selective chromatographic fractionation of catechol estrogens on anion exchangers in borate form.

The borate form of anion exchangers has been investigated for its utility in the field of estrogen analysis. The borate form of a weak (DEAE-Sephadex A-25) and a strong (QAE-Sephadex A-25) anion exchanger was easily prepared by appropriate washing of the gels, without the need of time consuming immobilization techniques. Estrogens with vicinal cis-hydroxyls were strongly retained in both gels through formation of borate complexes and readily separated from estrogens not possessing such groups. Moreover, borate complex formation with the labile o-dihydroxyphenyl moiety of catechol estrogens fully protected them from decomposition during chromatography. Quantitative recovery of catechol estrogens was thereby obtained without use of antioxidants. The borate form of QAE-Sephadex A-25 was capable, in addition, of separating estrogens not possessing vicinal cis-hydroxyls from the corresponding neutral steroids.

Anion Exchange Resins↗
PubMed1984

In vitro metabolic conjugation of catechol estrogens.

In vitro metabolic conjugation of the catechol estrogens, 2-hydroxyestrone and 4-hydroxyestrone, has been investigated by means of HPLC with electrochemical detection. Sulfation of 2-hydroxyestrone and 4-hydroxyestrone with the rat liver 105 000 g supernatant fortified with 3'-phosphoadenosine-5'-phosphosulfate provided the 2- and 4-monosulfates, respectively. Glucuronidation of the two catechols with the rat and human liver 1500 g supernatant in the presence of uridine-5'- phosphoglucuronic acid gave the 2- and 4-glucuronides, respectively. In contrast, incubation with the guinea pig liver 1500 g supernatant yielded both isomeric monoglucuronides . When 2'-hydroxyestrone was incubated with rat liver 1500 g supernatant and S-adenosyl-L-methionine, the 2- and 3-monomethyl ethers were formed in an equal amount, while 4-hydroxyestrone was transformed into the 4-methyl ether in 12 times greater yield than the 3-methyl ether. The participation of sulfation and glucuronidation in the formation of guaiacol estrogens is discussed.

Animals↗
PubMed1988

Inhibition of catechol estrogen formation in rat liver microsomes by hormonal steroids and related compounds.

The inhibitory action of a number of different hormonal steroids and related compounds on the 2-hydroxylation of estradiol by male rat liver microsomes was examined by a radiometric assay. Progesterone, Diethylstilbestrol, testosterone and 4-androstenedione were found to be the most potent of the compounds tested but inhibition was also observed with other steroids and a group of androgen analogs which are aromatization inhibitors. The kinetic constant Ki for those steroids which gave linear double reciprocal plots when added to [2-3H]estradiol was determined and the products from [14C]estradiol in the presence of the inhibitors were examined by TLC and autoradiography. The addition of steroids with a 17-hydroxyl group such as testosterone or dihydroequilin resulted in the formation of mainly 2-hydroxyestradiol with smaller amounts of other metabolites while those with a reducible ketonic group such as progesterone, 4-androstenedione, equilin or equilenin gave rise to considerable amounts of estrone in addition to the catechol estrogens. Further purification of the liver microsomes did not alter this effect. The possible role of progesterone and the catechol estrogens in the control of estrogen hydroxylation in liver as well as other aspects of steroid interaction are discussed.

Androgens↗
PubMed1990

Coordinated induction of estrogen hydroxylase and catechol-O-methyl transferase by xenobiotics in first trimester human placental explants.

The estrogen phenol A-ring metabolism was investigated in the first trimester placenta using radioenzymatic techniques. In untested explants cultured for 16 h, estrogen hydroxylase (EH) but not catechol-O-methyl transferase (COMT) activity was increased significantly 1.8-fold (P less than 0.05). Cultures made in the presence of chemoprotectors, 25 microM of 1-phenylazo-2-naphthol (Sudan I) and coumarin but not 2(3)-tert-butyl-4-hydroxyanisole (BHA) caused a significant increase in EH activity, 1.8- and 2.2-fold, respectively (P less than 0.05). This was coupled with a significant, P less than 0.05, increase in the COMT activity by 25 microM of all three chemoprotectors, BHA, Sudan I, and coumarin, 2.7-, 2.3-, and 2-fold respectively. The carcinogens benzo(a)pyrene and 20-methylcholanthrene at 50 microM concentration, however, had no effect upon both enzymes' activity. Finally, the two enzymes's activities were correlated under the experimental conditions tested. Except for zero time where no correlation was found (r2 = 0.3), in all other experimental conditions, a significant (r2 = 0.75) correlation was observed. In conclusion, EH and COMT enzyme activities appear to undergo a coordinated induction in cultured placental explants in the first trimester. The implications of catechol metabolism for embryonal development are discussed.

Butylated Hydroxyanisole↗
PubMed1993

Enzymatic O-methylation of catechol estrogens in red blood cells: differences in animal species and strains.

Enzymatic O-methylation of catechol estrogens in red blood cells has been investigated with respect to species difference. In the presence of S-adenosylmethionine, 2- or 4-hydroxyestradiol (2-OHE2 or 4-OHE2) was incubated with blood lysate obtained from rats (five strains), guinea pigs, mice, rabbits, dogs, monkeys, and humans, respectively. The yielded guaiacols and unchanged substrate were determined by gas chromatography/mass spectrometry in a selected ion monitoring mode employing the corresponding 2H4-labeled compounds as internal standards. The total amounts of guaiacols formed from 2-OHE2 and 4-OHE2 were different, being the highest (79.6% and 38.1%) in monkeys and the lowest (5.1% and 1.9%) in humans. The ratios of isomeric guaiacols formed from 4-OHE2 (4Me/3Me) were 7.6-71, while those from 2-OHE2 (2Me/3Me) were 1.4-3.2. Thus, marked differences in O-methylation of catechol estrogens were observed among animal species, but no significant strain difference was detected in rats.

Adult↗
PubMed1989

Abnormal neurulation induced by 7-hydroxy-2-acetylaminofluorene and acetaminophen: evidence for catechol metabolites as proximate dysmorphogens.

Direct additions to culture media of either acetaminophen (APAP) or 7-hydroxy-2-acetylaminofluorene (7-OH-AAF) resulted in abnormal closure of the anterior neuropores of cultured rat embryos in the absence of an exogenous bioactivation system. Concentrations required to produce a 50% incidence of the defect were approximately 500 and 250 microM for APAP and 7-OH-AAF, respectively. Losses of viability were not evident at these concentrations but 7-OH-AAF elicited a somewhat greater effect on growth parameters and generalized embryotoxicity. Transplacental induction with 3-methylcholanthrene (MC) of P450IA1 in subsequently cultured rat embryos did not detectably alter the capacity of APAP or 7-OH-AAF to effect embryotoxicity or neuropore closure. However, additions to the culture medium of exogenous hepatic bioactivating systems (S9) from MC-induced vs phenobarbital (PB)-induced adult rats produced profoundly different effects on neuropore closure. Coincubation with S9 from MC-induced rats reduced the incidence of 7-OH-AAF-elicited abnormal neuropores from 45 to 19%, whereas coincubation with S9 from PB-induced rats increased the incidence to 77%. Coincubation with MC-induced S9 produced no statistically significant effect on APAP-elicited neuropore abnormalities but, with PB-induced S9, resulted in a significant increase from 60 to 86%. Additions of 3-OH-APAP (0.1-0.2 mM) but not N-acetyl-p-benzoquinoneimine (NAPQI, 0.1-0.5 mM) to the culture medium elicited the typical neuropore abnormality. Experiments with APAP and 7-OH-AAF as substrates demonstrated that embryonic enzymes catalyzed their conversion to the corresponding catechols. Considered together, the results provided evidence that embryonic conversion of APAP or 7-OH-AAF to the corresponding catechol metabolites may be instrumental in effecting the abnormal anterior neuropore closure observed after exposure of embryos to the respective parent compounds.

2-Acetylaminofluorene↗
PubMed1983

Catechol-O-methyltransferase activity and aminergic binding sites distribution in human peripheral blood lymphocyte subpopulations.

We have studied the binding of [3H]dihydroalprenolol, a beta-adrenergic ligand, and [3H]spiroperidol, a dopaminergic ligand, to human peripheral blood lymphocyte subpopulations. The catechol-O-methyltransferase activity on these different cells was also determined. On intact living cells, an unequal distribution of both beta-adrenergic and dopaminergic binding sites was found between B- and T-lymphocyte subpopulations. In each binding, T cells exhibited a lower number of binding sites than B cells. On particulate preparation, catechol-O-methyltransferase activity showed a similar distribution, but binding data with such material were quite different. Although it was not possible to detect dopaminergic binding sites on particulate preparation, T and B lymphocytes contained equivalent numbers of beta-adrenergic binding sites. Different explanations for these results are proposed.

B-Lymphocytes↗
PubMed1985

HPLC-ECD procedure for the measurement of O-methylation of catechol estrogens by vascular tissue.

A precolumn extraction procedure combined with high-performance liquid chromatography with electrochemical detection (HPLC-ECD) has been developed for the identification and quantitation of catechol estrogens, their immediate precursors (estrogens), and their 0-methylated metabolites. These compounds were isolated from Krebs solutions and from perchloric acid tissue extracts or whole tissues by simple solvent extraction prior to quantitation. The optimal conditions for detection by HPLC-ECD were those employing a radial compression module, a C18 Bondapak cartridge, and an isocratic mobile phase of ammonium phosphate (pH 3.0) combined with 30-70% acetonitrile. A biological application of this procedure includes the investigation of the 0-methylation of catechol estrogens by vascular tissue. In the present study, the 0-methylation of 2-hydroxyestradiol by rabbit aorta has been examined. The 0-methylation in segments of thoracic aorta was significantly less than that in abdominal aortic segments, but was reproducible along the length of the thoracic aorta.

Animals↗
PubMed1995

Detection of salicylate and its hydroxylated adducts 2,3- and 2,5-dihydroxybenzoic acids as possible indices for in vivo hydroxyl radical formation in combination with catechol- and indoleamines and their metabolites in cerebrospinal fluid and brain tissue.

It has been suggested that salicylate (SA) hydroxylation can be used to detect hydroxyl radical formation in vivo. Here we describe a rapid and sensitive HPLC method using ultraviolet absorbance (UV) and electrochemical detection (EC) to detect SA (UV), its hydroxylated adducts 2,3- and 2,5-dihydroxybenzoic acids (DHBA) and catechol in combination with catechol- and indoleamines and related metabolites (EC) in one isocratic run. These compounds were measured in acidified cerebrospinal fluid (CSF) and perchlorate extracts of striatal tissues of untreated and SA-loaded rats (300 mg/kg SA, i.p.). Peaks were identified by comparing retention times of samples and standards, by adding standards to biological samples, by voltamograms, and by comparing chromatograms of manganese (Mn2+)-injected striata of SA-loaded rats with several control conditions. Six hours after unilateral injection of 0.4 mumol Mn2+ into striatum, 2,3-DHBA and 2,5-DHBA levels in striatum were respectively 4- and 7-fold increased as compared to non-injected (contralateral) striata, suggesting in vivo hydroxyl radical formation. In addition, dopamine and serotonin levels were depleted in Mn(2+)-injected striata by 46% and 64%, respectively. In CSF of Mn(2+)-injected rats, DHBA/SA ratios were not significantly changed as compared to those of control rats. In conclusion, the described technique can be applied to study in vivo hydroxyl radical formation in direct relation with dopaminergic and serotonergic neurotransmitter changes during neurotoxic processes.

Animals↗
PubMed1990

Immobilized and free cell continuous cultures of a recombinant E. coli producing catechol 2,3-dioxygenase in a two-stage chemostat: improvement of plasmid stability.

The immobilization of recombinant strains of E. coli W3110/pTG205 in K-carrageenan gel beads improves the plasmid stability during continuous cultures in the absence of selection pressure. Since, xyl E gene (which encodes catechol 2,3-dioxygenase from Pseudomonas putida) transcription is controlled by the trp promoter, the effects of tryptophan (repressor) and 3 beta-indolyl acrylic acid (derepressor) on pTG 205 stability and enzyme production have been studied in both free and immobilized cell cultures. A two-stage continuous culture system running for 150 h is described. In the first stage an immobilized culture is performed in the presence of tryptophan with a significant plasmid stability. The cells released from the gel beads are continuously transferred in the second stage reactor where expression is induced by 3 beta-indolyl acrylic acid. In these conditions an efficient production of catechol 2,3-dioxygenase is observed.

Biotechnology↗