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PubMed1978

Catechol-O-methyltransferase activity in erythrocytes of pregnant women.

Catechol-O-methyltransferase (COMT) is the enzyme that converts catechols, e.g., catecholamines and catechol estrogens, to their methyl ethers. COMT activity measured in erythrocytes (RBC's) of healthy men (No. = 47) and healthy nonpregnant women (No. = 53) was 8.2 +4- 0.17 nmoles X ml.-1 (mean and standard error). The COMT activity in RBC's of healthy pregnant women (No. = 100) was 10.7 +/- 0.29 nmoles X ml.-1 RBC X hr.-1, a value which is significantly higher than that found in RBC's of men and nonpregnant women (p less than 0.001).

Adolescent↗

PubMed1979

Alterations in activity of enzyme catechol-O-methyltransferase in central and peripheral regions of the rat and rabbit during pregnancy, parturition, and the postpartum period.

Natural variations in the activity of the enzyme catechol-O-methyltransferase in central and peripheral regions of the rat and rabbit during pregnancy and parturition were observed. All of the organs of the rat showed a decrease in enzyme activity up to the twenty-first day of pregnancy. Rabbit tissues also demonstrated a decrease in catechol-O-methyltransferase activity during Days 24 to 30 after coitus. Increases in activity of the rat ovary, brain, and hypothalamus took place from during Day 21 after coitus to the onset of parturition. The enzyme activity in the rat hypothalamus reached its maximum level at four hours post partum from the Day 21 value, but the rabbit hypothalamus showed the maximum activity at 0 hour parturition. During post partum hours, rat brain catechol-O-methyltransferase activity was very high but the rabbit brain showed a very low level of activity. Rabbit uterine activity reached its minimum value at Day 31 after coitus, but at the comparable intervals the situation was inversed in the rat. Results show an important modification of monoamine degradation by 3-O-methylation during midgestation in the central and peripheral regions. These modifications may be attributed to the natural variations in endocrine activity taking place during pregnancy.

Adrenal Glands↗

PubMed1991

Do catechol estrogens participate in the initiation of labor?

To assess the role of catechol estrogens in the initiation of labor, we compared the levels in amniotic fluid during the second and third trimesters and from women undergoing cesarean section at term not in labor and those with spontaneous labor at term. Catechol estrogen concentrations in amniotic fluid increased significantly with the progress of pregnancy. Further, concentrations (mean +/- SE) were significantly higher in spontaneous labor at term (468.6 +/- 29.5 pg/ml) compared with those obtained during cesarean section (242.6 +/- 22.3 pg/ml) at term not in labor. We suggest that catechol estrogens, through their stimulating effects on prostaglandin synthesis, participate in the initiation of labor.

Adult↗

PubMed1988

Purification and properties of catechol 1,2-dioxygenase (pyrocatechase) from Pseudomonas putida mt-2 in comparison with that from Pseudomonas arvilla C-1.

Catechol 1,2-dioxygenase (pyrocatechase) has been purified to homogeneity from Pseudomonas putida mt-2. Most properties of this enzyme, such as the absorption spectrum, iron content, pH stability, pH optimum, substrate specificity, Km values, and amino acid composition, were similar to those of catechol 1,2-dioxygenase obtained from Pseudomonas arvilla C-1 [Y. Kojima et al. (1967) J. Biol. Chem. 242, 3270-3278]. These two catechol 1,2-dioxygenases were also found, from the results of Ouchterlony double diffusion, to share several antigenic determinants. The molecular weight of the putida enzyme was estimated to be 66,000 and 64,000 by sedimentation equilibrium analysis and Sephadex G-200 gel filtration, respectively. The enzyme gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, corresponding to Mr 32,000. The NH2-terminal sequence, which started with threonine, was determined up to 30 residues by Edman degradation. During the degradation, a single amino acid was released at each step. The NH2-terminal sequence up to 20 residues was identical to that of the beta subunit of the arvilla enzyme, with one exception at step 16, at which arginine was observed instead of glutamine. The COOH-terminal residue was deduced to be arginine on carboxypeptidase A and B digestions and on hydrazinolysis. These results indicate that the putida enzyme consists of two identical subunits, in contrast to the arvilla enzyme which consists of two nonidentical subunits, alpha and beta [C. Nakai et al. (1979) Arch. Biochem. Biophys. 195, 12-22], although these two enzymes have very similar properties.

Amino Acid Sequence↗

PubMed1979

Catechols stimulate ferricyanide reduction in chloroplast photosystem II.

In isolated chloroplasts (Spinacia olearacea), where electron transport to Photosystem I is blocked by the plastoquinone antagonist, dibromothymoquinone, lipophilic catechols in concentrations of 50--150 microM stimulate ferricyanide reduction in Photosystem II and associated O2 evolution. Non-permeating catechols, such as Tiron, are unable to stimulate this reaction. Those quinones, such as 2,5-dimethylbenzoquinone, which act as class III electron acceptors, do not lead to stimulation of ferricyanide reduction in Photosystem II or stimulation fo associatied O2 evolution, when electron transport to Photosystem I is blocked by dibromoquinone. Stimulation of ferricyanide reduction is not observed in Tris-treated chloroplasts, implying that electron donation to Photosystem II by catechols is not responsible for the stimulation. Various mechanisms for this stimulation in class II chloroplasts are discussed.

Catechols↗

PubMed1977

Inhibition of lysyl hydroxylase by catechol analogs.

Catechol analogs inhibit the activity of lysyl hydroxylase (peptidyllysine, 2-oxyglutarate: oxygen 5-oxidoreductase, EC 1.14.11.4), a microsomal enzyme which catalyzes the transformation of certain lysyl residues in collagen to hydroxylysine. Chick embryo lysyl hydroxylase activity was measured by specific tritium release as tritiated water from an L-[4,5-3H]lysine-labelled unhydroxylated collagen substrate prepared from chick calvaria. Catechol analogs did not bind irreversibly to either enzyme or substrate, as full activity was restored with dialysis. Addition of excess cofactor, Fe2+, ascorbic acid, or alpha-ketoglutarate, did not affect inhibition. Kinetic analysis revealed that with respect to collagen substrate, catechol demonstrated a noncompetitive type of inhibition with a Ki of 15 muM.

Animals↗

PubMed1978

Purification and characterization of rat heart and brain catechol methyltransferase.

In an effort to detect the similarities and differences in the properties of rat heart, brain and liver catechol methyltransferase (S-adenosyl-L-methionine:catechol O-methyltransferase, EC 2.1.1.6), we have determined the cellular distribution of this enzyme activity and extensively purified the soluble and microsomal enzymes present in these tissues. Purification of soluble heart (688-fold) and brain enzymes (240-fold) were achieved using an affinity chromatographic system. The properties of these enzymes were compared with respect to their molecular weights, substrate specificities, inhibitor specificities and immunological properties. The characteristics of the enzyme active sites were investigated using various methyl acceptor substrates and various analogs of S-adenosylmethionine as methyl donors. A series of analogs of S-adenosylhomocysteine was also evaluated as inhibitors of these enzymes. The immunological properties of the purified soluble and microsomal enzymes from heart and brain were investigated using an antibody isolated from rabbits which had been immunized with the soluble rat liver enzyme. In general the properties of catechol methyltransferases isolated from heart and brain were similar to the properties of the enzyme isolated from liver. Some minor differences in substrate and inhibitor specificities were observed which might suggest slight differences in the active sites of these enzymes.

Animals↗

PubMed1983

The inhibition of catechol-O-methyltransferase by 2,3-dihydroxypyridine.

Despite its structural similarity to catechol, 2,3-dihydroxypyridine is not a substrate but a "dead-end" inhibitor of purified pig liver catechol-O-methyltransferase. It inhibits the methylation of 3,4-dihydroxyphenylacetic acid competitively with an inhibitor constant of 15 microM. Against the methyl donor, S-adenosyl-L-methionine, it is an uncompetitive inhibitor (Ki = 85 microM). Clearly, although 2,3-dihydroxypyridine interacts with the catechol-binding site of the enzyme, the presence of a nitrogen in the ring alters its susceptibility to O-methylation.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1987

Mechanism of antitumoral activity of catechols in culture.

Cell lines Raji and K 562, lacking tyrosinase, and two melanotic human melanoma cell lines (IRE 1 and IRE 2), were exposed to concentrations from 5 X 10(-3) M to 10(-5) M of different phenols which are substrates of tyrosinase, i.e. l-dopa, dopamine, hydroquinone, terbutylcatechol, and of phenols which are not substrates of the tyrosinase, i.e. resorcinol, butylated hydroxyanisole and hydroquinone dimethyl ether. Cultures were carried out in the presence or in the absence of oxygen radical scavenger enzymes superoxide dismutase, catalase and peroxidase. The stability of each substance in culture medium was assayed by high performance liquid chromatography (HPLC). Results showed that: catechols which are substrates of tyrosinase decompose fully after 24 hr in medium; they are equally toxic for melanoma and non-melanoma cell lines; their toxicity increases when they are preincubated in medium for 24 hr and 48 hr before addition of cells; their toxicity is significantly reduced by addition of scavenger enzymes; on the contrary, phenols not substrates of tyrosinase are stable in medium and their toxicity is not reduced by scavenger enzymes. It is concluded that tyrosinase does not play a major role in catechol toxicity in vitro, which is probably due to some products of catechol decomposition, especially oxygen radicals, acting outside the cells.

Anisoles↗

PubMed1991

Inhibition of tryptophan hydroxylase by benserazide and other catechols.

Tryptophan hydroxylase (L-tryptophan, tetrahydropteridine:oxygen oxidoreductase [5-hydroxylating]; EC 1.14.16.4; TPH), the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter serotonin, was inhibited directly by benserazide, an inhibitor of aromatic-L-amino-acid decarboxylase (3,4-dihydroxy-L-phenylalanine carboxy-lyase; EC 4.1.1.28; AAAD). Benserazide was a competitive inhibitor for the pterin cofactor tetrahydrobiopterin and an uncompetitive inhibitor for the substrate tryptophan. NSD 1015, another decarboxylase inhibitor, did not directly inhibit TPH. Other compounds with catechol moieties in their structures such as 3,4-dihydroxyphenylalanine (DOPA), dopamine, apomorphine, and SKF 38393 were also found to be potent inhibitors of TPH. These results indicate that drugs or neurotransmitters with catechol structures directly inhibit the activity of TPH and add to a growing body of evidence indicating that endogenous dopamine can exert untoward effects on serotonin neurons, including inhibition of TPH. Furthermore, the use of decarboxylase inhibitors to cause the accumulation of 5-hydroxytryptophan as an in vivo measure of TPH activity could be problematic, particularly when drugs with catechol structures or dopamine-releasing compounds are also administered.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1992

Reactions of glutathione with the catechol, the ortho-quinone and the semi-quinone free radical of etoposide. Consequences for DNA inactivation.

Etoposide [4'-demethylepipodophyllotoxin-9-(4,6-O-ethylidene-beta- D-glucopyranoside)] can be metabolized to DNA-inactivating catechol, ortho-quinone and semi-quinone free radical derivatives which may contribute to its cytotoxicity. In this paper, we examined in vitro whether glutathione (GSH), which is known to react easily with quinoid compounds, could interact with the active etoposide intermediates and in this way influence the cytotoxicity of the parent compound. To this end, reactions of GSH with the etoposide intermediates were studied, using HPLC and ESR measurements, together with the effects of GSH on the biological inactivation of single-stranded (ss) and double-stranded (RF) phi X174 DNA by these compounds. From the results it could be determined that: (a) GSH does not react with the catechol and, as a consequence, has no effect on the reaction of this intermediate of etoposide with ss and RF phi X174 DNA; (b) GSH reacts with the ortho-quinone most likely by formation of a conjugate and by two-electron reduction to the catechol, resulting in a partial protection of ss and RF phi X174 DNA against inactivation by this species; and (c) GSH protects ss phi X174 DNA against inactivation by the semi-quinone free radical of etoposide probably by conjugation with this species.

Bacteriophage phi X 174↗

PubMed1993

Interaction of the di-catechols rooperol and nordihydroguaiaretic acid with oxidative systems in the human blood. A structure-activity relationship.

The effects of the di-catechols rooperol [(E)-1,5-bis(3',4'- dihydroxyphenyl)pent-4-en-1-yne; P2] and nordihydroguaiaretic acid (NDGA) on oxidative systems in the human blood were investigated. P2 and NDGA gave comparable results in the inhibition of leukotriene synthesis in the polymorphonuclear leukocyte and prostaglandin synthesis in platelet microsomes. The oxidation states of myeloperoxidase in the presence of H2O2 were also similarly affected by both P2 and NDGA. In these systems, the 4'4'-beta-D-diglucopyranoside of rooperol, hypoxoside [(E)-1,5-bis(4' beta-D-glucopyranosyloxy-3'- hydroxyphenyl) pent-4-en-1-yne; P2A] had no effect. The only system which showed significant differences in the effects of the catechols was the red blood cell. NDGA in the presence of H2O2 had a pronounced haemolytic effect, which did not correlate with its ability to induce methaemoglobin formation, while P2 had a much lower haemolytic effect, but stimulated the oxidation of haemoglobin to a greater extent than NDGA. NDGA is more hydrophobic than P2 which would result in a greater membrane effect. The pent-4-en-1-yne chain which links the catechol moieties in P2 can take part in the resonance structures of the semiquinone free radical, thus assisting in its stabilization and leading to increased methaemoglobin formation. This stabilization is also demonstrated by the fact that P2A affected the oxidation of haemoglobin to nearly the same extent as NDGA.

Blood Platelets↗

PubMed1980

Effect of catechol on the discharge of muscle spindle afferents from the hind limb of the rat.

Previous work had shown that some of the effects of catechol could be via the fusimotor system. In order to determine the extent of fusimotor involvement, recordings have been made from muscle spindle afferents in split dorsal root filaments of anaesthetised rats. Catechol failed to excite de-efferented muscle spindles therefore eliminating many possible non-fusimotor effects. Over 80% of spindle afferents with intact efferents showed increased discharge frequency 1 min after injection, this increase often following a biphasic pattern with a pronounced pre-myoclonic burst and decline followed by a more sustained period of activity during the myoclonic phase. Analysis of spontaneous twitches or twitches evoked by ipsilateral auditory stimulation showed in addition a phasic increase in discharge suggesting alpha-gamma co-activation. Both primary and secondary afferents from many muscle groups around ankle and toes had their discharge frequencies elevated. Elevation of discharge frequencies of secondaries implies increased gamma-s activity confirmed by a decrease in dynamic index. Both gamma-d and gamma-s involvement in catechol action on primaries is suggested by dynamic index measurements. Perhaps a more continuous form of testing such as sinusoidal stretches would reveal any rapid switching between activities in the two systems.

Afferent Pathways↗

PubMed1992

Determination of the catechol-O-methyltransferase inhibitor Ro 40-7592 in human plasma by high-performance liquid chromatography with coulometric detection.

A sensitive and specific high-performance liquid chromatographic method has been developed to measure the catechol-O-methyl-transferase (COMT) inhibitor 3,4-dihydroxy-4'-methyl-5-nitrobenzophenone (Ro 40-7592) in human plasma. The compound and the internal standard were extracted from plasma at pH 2 with n-butyl chloride-ethyl acetate (95:5, v/v). The extract was chromatographed on a reversed-phase column (Hypersil ODS, 5 microns) using a mixture of phosphate buffer (0.05 M, pH 2), methanol and tetrahydrofuran (45:55:5, v/v/v) as the mobile phase. Long-retained components were removed from the system by means of a simple column-switching system. Quantification of the catechol-O-methyltransferase inhibitor was performed by means of coulometric detection (0.1 V). The limit of quantification was about 1 ng/ml, using a 1-ml specimen of plasma. The recovery from human plasma was greater than 88%. The mean inter-assay precision was 5.3% in the range 2.5-1000 ng/ml. Linearity of the standard curve was obtained in the concentration range 2.5-500 ng/ml. The catechol-O-methyltransferase inhibitor was stable in human plasma when stored for six months at -20 degrees C and for 24 h at room temperature. The practicability of the new method was demonstrated by the analysis of more than 400 plasma samples from a tolerance study performed in human volunteers.

Benzophenones↗

PubMed1988

Differential effect of Cu2+ and Zn2+ on the formation and further metabolism of catechol estrogen by rat liver microsomes.

The action of a number of different divalent metal ions on the rat liver microsomal release of 3H2O from estradiol and 2-hydroxyestradiol labeled with 3H at C-2 or C-4 was investigated. Cu2+ at low concentration (10 microM) produced a marked and specific inhibition of the 2-hydroxylation of estradiol with virtually no effect on the further oxidative activation of catechol estrogen. In contrast, Zn2+ inhibited the interaction of 2-hydroxyestradiol with microsomal protein as measured by the release of 3H from C-4 of the labeled steroids but did not influence 2-hydroxylation, except at high concentration. Other metal ions tested produced little or no change. Cu2+ inhibited the irreversible binding of estradiol to protein but activated this reaction with the catechol estrogen as substrate. The action of both Cu2+ and Zn2+ was reversed by glutathione. The differential effect of these metal ions on estrogen metabolism gives additional support for two different mechanisms in the cytochrome P-450-catalyzed formation of catechol estrogens and their further activation to form protein conjugates.

Animals↗

PubMed1991

Influence of indole-3-carbinol on the hepatic microsomal formation of catechol estrogens.

The oral administration of indole-3-carbinol (IC), present in cabbage and other members of the Cruciferae family, to female rats almost doubled their ability to convert estradiol to catechol estrogens in the liver. This was determined by the release of 3H from C-2 of the estrogen and also by isolation of the 14C-labeled catechol derivative after incubation with hepatic microsomal fractions. The yield of 4-hydroxyestradiol was also elevated and these effects were similar to those produced by 3-methylcholanthrene (MC), a well-characterized cytochrome P450 inducer. Further evidence for the involvement of a mixed-function oxidase was provided by a 70% to 80% decrease in the yield of 3H2O and water-soluble radioactivity by SKF-525A (0.1 mM) when added to the microsomal fractions isolated from the livers of control or IC-treated rats. In addition, NADPH could not be replaced by NADH in these experiments. Pretreatment with ethionine prevented the increase in estradiol metabolism brought about by oral administration of IC. Both IC and MC inhibited catechol estrogen formation when added directly to the liver microsomal system, confirming earlier findings that in vivo inducers can act as in vitro inhibitors. However, IC was less inhibitory than MC, supporting the theory that IC is converted to a more active product in the stomach. Thus, IC may be conferring protection against estrogen-dependent neoplasia by increasing the hepatic oxidation of estradiol, thereby lowering the amount of available active estrogen.

Animals↗

PubMed1992

Synthesis of prostaglandins by pig blastocysts cultured in medium containing estradiol or catechol estrogen.

Two experiments were conducted to determine the effects of 2-hydroxy-estradiol-17 beta (2-OH-E2; 0, 50 and 100 microM) and estradiol-17 beta (E2; 0, 25 and 50 microM) on prostaglandin (PG) E and PGF2 alpha synthesis by day-10 pig blastocysts (day 0 is first day of estrus). Blastocysts were incubated in a modified Krebs-Ringer bicarbonate medium, supplemented with bovine serum albumin (4 mg/ml) and the vitamins and amino acids (essential and nonessential) in Minimum Essential Medium (without phenol red or antibiotics). The incubations were conducted at 39 degrees C for three 2-h periods; the second and third periods included an E2 or catechol estrogen treatment. Release of PGF2 alpha into the culture medium decreased (p less than 0.001) linearly with increasing concentrations of 2-OH-E2 in both periods. Release of PGE was not affected by 2-OH-E2, therefore 2-OH-E2 increased (p less than 0.06) the PGE:PGF2 alpha. When E2 was added to the medium, release of PGE was decreased (p less than 0.01) during the second and third periods. Release of PGF2 alpha also was decreased (p less than 0.05) by E2 during period 2, but E2 did not alter the PGE:PGF2 alpha. Content of PGs in blastocysts at recovery was less than 10% of the PGs released in vitro. Therefore, these studies demonstrate effects of both the primary and catechol forms of E2 on the synthesis of PGE and PGF2 alpha. Catechol estrogens and E2 may inhibit PG synthesis and modify the PGE:PGF2 alpha during the establishment of pregnancy in pigs.

Animals↗

PubMed1977

Role of catechol estrogens in activation of lordosis in female rats and guinea pigs.

In a variety of experiments, we tested the effectiveness of the 2-hydroxylated estrogen in facilitating sexual receptivity. A single injection of 2-hydroxy-estradiol-17beta (2-OHE2) to ovariectomized rats or 2-hydroxy-estrone (2-OHE1) to ovariectomized guinea pigs was ineffective in priming animals for facilitation of sexual receptivity even when a subsequent injection of progesterone was administered. The only facilitatory effect of catechol estrogens on lordosis that was demonstrated in this study occurred when 2-OHE2 was injected in combination with E2 and a subsequent injection of progesterone was given to rats. These results suggest a cooperatively between catechol estrogen and E2, but they also indicate that catechol estrogens, by themselves, do not play a crucial role in mediating sexual receptivity in rodents.

Animals↗