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PubMed2006

Prostaglandin J2 reduces catechol-O-methyltransferase activity and enhances dopamine toxicity in neuronal cells.

There is clear evidence that an inflammatory reaction is mounted within the CNS following trauma, stroke, infection and seizures, thus augmenting brain damage. Furthermore, chronic inflammation of the CNS is implicated in many neurodegenerative disorders. However, the effects of products of inflammation on neuronal cells are poorly understood. Herein, we characterize the effects of a neurotoxic product of inflammation, prostaglandin J2 (PGJ2), on catechol-O-methyltransferase (COMT) in human dopaminergic-like neuroblastoma SK-N-SH cells and rat (P2) cortical neurons. COMT metabolizes catechols and catecholamines, a pathway relevant to neurodegeneration. PGJ2 treatment reduced the expression and activity of COMT, induced its sequestration into perinuclear aggregates and potentiated dopamine toxicity. The large COMT aggregates were co-localized with the centrosome, suggesting an aggresome-like structure. Our results indicate that COMT impairment induced by PGJ2 treatment may increase the concentration of dopamine (or its metabolites) to neurotoxic levels. Thus, COMT impairment following pro-inflammatory events may be a potential risk factor in neurodegeneration.

Animals↗
PubMed2001

Entacapone: a catechol-O-methyltransferase inhibitor for the adjunctive treatment of Parkinson's disease.

BACKGROUND: When levodopa therapy is used in Parkinson's disease, degradation of the drug in the peripheral nervous system is associated with dyskinesias and motor fluctuations. Much of this degradation is produced by catechol-O-methyltransferase (COMT), an enzyme involved in the metabolism of catecholamines and catechol compounds. Inhibition of COMT activity prolongs the action of levodopa and reduces fluctuations in response. Entacapone is a selective inhibitor of COMT whose activity is primarily in the peripheral nervous system, with little effect in the central nervous system. OBJECTIVE: This paper reviews the pharmacologic properties and clinical usefulness of entacapone in the treatment of Parkinson's disease. METHODS: Recent studies, abstracts, and reviews published in the English-language literature were identified through searches of MEDLINE (1966-September 2000), International Pharmaceutical Abstracts (1970-September 2000), and PharmaProjects (September 2000 version), and from the Web sites of Parkinson's disease conferences held from 1996 to September 2000. Relevant human studies provided further information on the pharmacologic properties and clinical usefulness of entacapone. RESULTS: Entacapone is rapidly absorbed, with a time to maximum concentration of approximately 1 hour. Its plasma elimination half-life is 0.4 to 0.7 hour in the beta phase and 2.4 hours in the gamma phase, and it has 35% absolute bioavailability after oral administration, secondary to first-pass clearance. Entacapone is 98% protein bound; thus, it is not distributed widely in tissues and is almost completely metabolized before excretion (0.1%-0.2% of dose unchanged in urine). The drug inhibits erythrocyte-soluble COMT activity in a dose-dependent fashion (48% after a 400-mg dose, 82% after an 800-mg dose). The inhibitory effect is reversible, with recovery of soluble COMT activity within 4 to 8 hours. In levodopa-treated patients with Parkinson's disease who experience motor fluctuations, clinical trials have demonstrated entacapone's effectiveness in increasing "on" time (the period during which medications relieve the symptoms of Parkinson's disease) by up to 1.2 hours, decreasing "off" time (the period during which symptoms increase) by 0.9 to 1.3 hours, and producing overall total improvement in scores on the Unified Parkinson's Disease Rating Scale. The recommended dosage of entacapone is 200 mg administered orally with each dose of levodopa/carbidopa, up to 8 doses per day. The drug is generally well tolerated, with most adverse effects attributed to levodopa-related dopaminergic effects, including dyskinesias and nausea. CONCLUSIONS: In clinical trials, adjuvant treatment with entacapone appeared to be an effective and well-tolerated therapeutic strategy in patients with Parkinson's disease who experience fluctuations in the response to levodopa therapy. The increased elimination half-life of levodopa with concomitant entacapone results in greater and more sustained plasma levodopa levels, with more constant dopaminergic stimulation in the brain and greater amelioration of parkinsonian symptoms.

Antiparkinson Agents↗
PubMed1998

Transcriptional activation of the catechol and chlorocatechol operons: variations on a theme.

The ortho-cleavage pathways of catechol and 3-chlorocatechol are central catabolic pathways of Pseudomonas putida that convert aromatic and chloroaromatic compounds to tricarboxylic acid (TCA)-cycle intermediates. They are encoded by the evolutionarily related catBCA and clcABD operons, respectively. Expression of the cat and clc operons requires the LysR-type transcriptional activators CatR and ClcR, and the inducer molecules cis,cis-muconate and 2-chloro-cis,cis-muconate. In addition to sequence similarities, CatR and ClcR share functional similarities which allow catR to complement clcR mutants. DNase-I footprinting, DNA bending and in vitro transcription analyses with RNA polymerase mutants indicate that CatR and ClcR activate transcription via a similar mechanism which involves interaction with the C-terminal domain of the alpha-subunit (alpha-CTD) of RNA polymerase. In vitro transcription assays with different regions of the clc promoter indicate that the ClcR dimer bound to the promoter proximal site (the activation binding site) interacts with the alpha-CTD. Gel shift assays and DNase-I footprinting have demonstrated that CatR occupies two adjacent sites proximal to the catBCA promoter in the presence of inducer and an additional binding site within the catB structural gene called the internal binding site (IBS). CatR binds the IBS with low intrinsic affinity that is increased by cooperativity in presence of the two promoter binding sites. Site-directed mutations in the IBS indicate a probable cis-acting repressor function for the IBS. The location of the IBS within the catB structural gene, the cooperativity observed in footprinting studies and phasing studies suggest that the IBS participates in the interaction of CatR with the upstream binding sites by looping out the intervening DNA. Although the core transcriptional activation mechanisms of CatR and ClcR have been conserved, nature has provided some flexibility to respond to different environmental signals in addition to the presence of inducer. Transcriptional fusion studies demonstrate that the expression from the clc promoter is repressed when the cells are grown on succinate, citrate or fumarate and that this repression is ClcR-dependent and occurs at the transcriptional level. The presence of these organic acids did not affect the expression from the cat promoter. In vitro transcription assays demonstrate that the TCA-cycle intermediate, fumarate, directly and specifically inhibits the formation of the clcA transcript. No such inhibition was observed when CatR was used as activator on either the cat or clc template. Since both the catechol and the chlorocatechol pathways feed into the TCA cycle, but only the chlorocatechol pathway is inhibited by fumarate, there is a subtle difference in the regulation of these two pathways where intracellular sensing of a TCA-cycle intermediate leads to a reduction of chloroaromatic degradation.

Bacterial Proteins↗
PubMed2006

Coupling between protein and reaction dynamics in enzymatic processes: application of Grote-Hynes Theory to catechol O-methyltransferase.

The generalized Langevin equation (GLE)-based Grote-Hynes (GH) theory is used to calculate the transmission coefficients, kappa, for the methyl transfer from S-adenosylmethionine to catecholate both in aqueous solution and in the catechol O-methyltransferase active site. Values of kappa, which measures the deviation of the rate constants from the Transition State Theory (TST) predictions, are obtained by means of rare event molecular dynamics simulations. The results are 0.62 +/- 0.04 and 0.83 +/- 0.03 for the aqueous and enzymatic environments, respectively, while the Grote-Hynes predictions are 0.58 +/- 0.09 and 0.89 +/- 0.03, respectively. The Kramers theory estimates are much smaller, about 0.01 and 0.1, respectively. Thus, the enzymatic transmission coefficient is closer to TST predictions than the value obtained in solution. In addition, our results show that the enzymatic coefficient is also closer to its nonadiabatic (or frozen environment) limit than is the solution coefficient. These findings can be understood considering that, during the passage over the barrier top, there is a smaller coupling between the reactive system and the environment in the enzyme than in solution, as well as a smaller reorganization suffered by the enzyme. Analysis of the transition state friction kernel leads to the identification of some key vibrational modes governing the coupling between the two different environments and the reacting solute in the transition state region and insights on their relevance for the reaction dynamics' influence on the transmission coefficient.

Catechol O-Methyltransferase↗
PubMed2002

Synthesis of 1-(3,4-dihydroxy-5-nitrophenyl)-2-phenyl-ethanone and derivatives as potent and long-acting peripheral inhibitors of catechol-O-methyltransferase.

A homologous series of novel nitro-catechol structures (7a-7e) were synthesized and tested as inhibitors of the enzyme catechol-O-methyltransferase (COMT). Increasing chain length was found to have significant impact on both brain penetration and duration of COMT inhibition in the rat. Of this series, compound 7b (1-(3,4-dihydroxy-5-nitrophenyl)-2-phenyl-ethanone) was found to exhibit the most potent and selective inhibition of peripheral COMT, with an inhibition profile more similar to entacapone 2 than tolcapone 1 (an equipotent peripheral and central inhibitor) but with much improved duration of action (7b, 70% inhibition and 2, 25% inhibition at 9 h after administration). The effects of structural modifications to 7b on COMT inhibitory profile were investigated, and it is concluded that the carbonyl group and preferably unsubstituted aromatic ring are essential features to maintain prolonged peripheral COMT inhibition. The introduction of the alpha-methylene group, the major structural difference between 7b and 1, would appear responsible for the observed enhancement in selectivity of peripheral COMT inhibition of 7b, which has more limited access to the brain than 1.

Acetophenones↗
PubMed2005

Synthesis and biological evaluation of a novel series of "ortho-nitrated" inhibitors of catechol-O-methyltransferase.

Novel regioisomeric "ortho-nitrated" catechols related to the catechol-O-methyltransferase (COMT) inhibitors BIA 3-202 3 and BIA 3-335 4 were synthesized and biologically evaluated. Changing the position of the nitro group from the "classical" meta- to the ortho-position relative to the side-chain substituent of the nitrocatechol pharmacophore exerted profound effects on selectivity and duration of COMT inhibition. Alkylaryl compounds 7a-d possessed shorter duration of action than their regioisomers, but 7b displayed reversed selectivity over 3 at 3 and 6 h, exhibiting preferential central inhibition. In the amino-substituted series, ortho-nitrated regioisomer 14k was less peripherally selective than 4 and short-acting, whereas decahydroquinoline 14g displayed an unprecedented combination of long-acting and selective peripheral inhibition. 7b could provide a useful tool to probe the pharmacological utility of short-acting, centrally selective COMT inhibitors in the treatment of depression in Parkinsonian patients, and 14g represents a promising candidate for clinical evaluation as an adjunct to L-Dopa therapy.

Animals↗
PubMed1990

Exercise hemodynamics and catecholamine metabolism after catechol-O-methyltransferase inhibition with nitecapone.

The effect of catechol-O-methyltransferase inhibition with nitecapone (OR-462) on the hemodynamic responses to exercise and catecholamine metabolism was studied in 10 healthy male volunteers (aged 19 to 26 years). Nitecapone, a new specific and selective catechol-O-methyltransferase inhibitor, was given at increasing single oral doses up to 100 mg. Nitecapone did not influence resting or exercise heart rate, blood pressure, systolic time intervals, or plasma catecholamine levels. It altered the metabolic profile of catecholamines as shown by (1) an increase of 140% in the plasma concentration of the monoamine oxidase-dependent metabolite 3,4-dihydroxyphenylethyleneglycol (p less than 0.001), (2) a decrease of 27% in the plasma concentration of its methylation product 3-methoxy-4-hydroxyphenylethyleneglycol (p less than 0.05), and (3) a 25% reduction in the urinary excretion of the methylated metabolites 3-methoxy-4-hydroxymandelic acid and homovanillic acid (p less than 0.05). Nitecapone was well tolerated and seemed to be hemodynamically safe in humans.

Adult↗
PubMed1996

Inhibition of catechol O-methyltransferase-catalyzed O-methylation of 2- and 4-hydroxyestradiol by quercetin. Possible role in estradiol-induced tumorigenesis.

Catecholestrogens have been postulated to mediate the induction of kidney tumors by estradiol in male Syrian hamsters. In this study, we examined the mechanism of inhibition by quercetin of the catechol O-methyltransferase-catalyzed O-methylation of catecholestrogens as a basis for the previously reported enhancement of estradiol-induced tumorigenesis by this flavonoid. In hamsters treated with 50 micrograms of [6,7-3H]estradiol, quercetin increased concentrations of 2- and 4-hydroxyestradiol in kidney by 80 and 59%, respectively. In animals treated with two 10-mg estradiol implants, quercetin also decreased by 63-65% the urinary excretion of 2- and 4-hydroxyestradiol monomethyl ethers. Taken together, these results demonstrate the in vivo inhibition of the O-methylation of catecholestrogens by quercetin. S-Adenosyl-L-homocysteine, produced by the methylation of catecholestrogens, noncompetitively inhibited the O-methylation of 2- and 4-hydroxyestradiol by hamster kidney cytosolic catechol O-methyltransferase (IC50 approximately 10-14 microM). Due to the rapid O-methylation of quercetin itself, quercetin decreased renal concentrations of S-adenosyl-L-methionine by approximately 25% in control or estradiol-treated hamsters and increased concentrations of S-adenosyl-L-homocysteine by 5-15 nmol/g of wet tissue, which was estimated to cause a 30-70% inhibition of the enzymatic O-methylation of catecholestrogens. Quercetin or fisetin (a structural analog) inhibited the O-methylation of 2- and 4-hydroxyestradiol by a competitive plus noncompetitive mechanism (IC50 approximately 2-5 microM). These results suggest that the in vivo O-methylation of catecholestrogens is inhibited more by S-adenosyl-L-homocysteine than by quercetin. The accumulation of 2- and 4-hydroxyestradiol during co-administration of estradiol and quercetin may enhance metabolic redox cycling of catecholestrogens and thus estradiol-induced kidney tumorigenesis.

Animals↗
PubMed1980

Methyl conjugation in uraemia: catechol-O-methyltransferase.

1 Erythrocyte (RBC) catechol-9-methyltransferase (COMT) activity is significantly higher in erythrocytes from uraemic patients on maintenance haemodialysis, 18.7 +/- 1.4 units/ml RBC (mean +/- s.e. mean, n = 22) than in the blood of randomly selected subjects, 12.0 +/- 0.2 units/ml (mean +/- s.e. mean, n = 557, P < 0.001). 2 Uraemic plasma contains larger quantities of endogenous methyl acceptors than does normal plasma, and it reversibly inhibits RBC lysate COMT activity to a greater degree than does normal plasma. 3 There are large individual variations in the degree of inhibition of RBC COMT activity plasma from patients with renal failure. Inhibition varied from 10-43% when 40 microliters plasma from each of 19 randomly selected uraemic patients was tested, and there as a direct correlation between the inhibition of COMT by plasma from an individual uraemic patient and its content of endogenous methyl acceptors (r = 0.64, n = 19, P < 0.01). 4 Kinetic studies with pooled uraemic plasma demonstrate that inhibition of COMT by uraemic plasma is uncompetitive with respect to both the catechol substrate and the methyl donor for the reaction, S-adenosyl-L-methionine. 5 Plasma from uraemic patients does not inhibit partially purified rat liver COMT, an observation which suggests that the inhibition is not due to a direct effect on COMT but requires the presence of other constituents of the RBC lysate, perhaps other methyltransferase enzymes.

Animals↗
PubMed1994

Characterization of phe B gene encoding catechol 2,3-dioxygenase.

DNA sequence of the phe B gene isolated from a chromosome of the phenol degrading bacterium Pseudomonas putida BH is identical to that of the dmp B gene from the phenol degradative plasmid, pVI150. Catechol 2,3-dioxygenase encoded by phe B showed similar substrate specificity to that of xyl E. However, Phe B has much smaller Km values than Xyl E, indicating that Phe B is useful for treatment of low concentrations of catechol derivatives in waste water.

Biodegradation, Environmental↗
PubMed1994

Comparison of two new inhibitors of catechol O-methylation on striatal dopamine metabolism: a microdialysis study in rats.

1. Effects of two new inhibitors of catechol O-methylation (CGP 28014 and entacapone; 30 mg kg-1, i.p.) were compared by means of brain microdialysis in rats treated with L-3,4-dihydroxyphenylalanine (L-dopa)/carbidopa (50/50 mg kg-1, i.p., respectively) or saline. 2. In saline-treated rats, CGP 28014 maximally (max) increased striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) effluxes by 41% and 49%, respectively, whereas homovanillic acid (HVA) levels were decreased by 71%. 3. In the presence of L-dopa/carbidopa, a peripherally active inhibitor of catechol O-methyltransferase (COMT) entacapone had a short-lasting increasing effect on L-dopa efflux. Compared to the effects of L-dopa/carbidopa alone 3-O-methyldopa (3-OMD) levels were effectively reduced (max 79%) by entacapone, but not by CGP 28014. 4. Entacapone, in contrast to CGP 28014, increased striatal dopamine efflux (max 492% of that after L-dopa/carbidopa alone). Also DOPAC levels were increased by entacapone (255% at 180 min), but not significantly by CGP 28014 (159% at 180 min). 5. Both compounds initially decreased HVA efflux. The effect of CGP 18014 was longer-lasting. By the end of the measurement, entacapone even increased HVA levels (max 259%). 6. Our results demonstrate that entacapone is a peripheral COMT inhibitor and support the view that CGP 18014 is mainly a centrally acting inhibitor of O-methylation.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2002

Kinetics and crystal structure of catechol-o-methyltransferase complex with co-substrate and a novel inhibitor with potential therapeutic application.

Catechol-O-methyltransferase (COMT; E.C. 2.1.1.6) is a ubiquitous enzyme in nature that plays an important role in the metabolism of catechol neurotransmitters and xenobiotics. In particular, inactivation of drugs such as L-3,4-dihydroxyphenylalanine (L-DOPA) via O-methylation is of relevant pharmacological importance, because L-DOPA is currently the most effective drug used in the treatment of Parkinson's disease. This justified the interest in developing COMT inhibitors as potential adjuncts to L-DOPA therapy. The kinetics of inhibition by BIA 3-335 (1-[3,4-dihydroxy-5-nitrophenyl]-3-(N-3'-trifluormethylphenyl)-piperazine-1-propanone dihydrochloride) were characterized using recombinant rat soluble COMT. BIA 3-335 was found to act as a potent, reversible, tight-binding inhibitor of COMT with a K(i) of 6.0 +/- 1.6 nM and displaying a competitive inhibition toward the substrate binding site and uncompetitive inhibition toward the S-adenosyl-L-methionine (SAM) binding site. The 2.0-A resolution crystal structure of COMT in complex with its cosubstrate SAM and a novel inhibitor BIA 3-335 shows the atomic interactions between the important residues at the active site and the inhibitor. This is the first report of a three-dimensional structure determination of COMT complexed with a potent, reversible, and tight-binding inhibitor that is expected to have therapeutic applications.

Animals↗
PubMed1980

Preferential utilization of phenol rather than glucose by Trichosporon cutaneum possessing a partially constitutive catechol 1,2-oxygenase.

A phenol-utilizing yeast, Trichosporon cutaneum POB 14, which has a partially constitutive activity of catechol 1,2-oxygenase, utilized phenol in preference to glucose in a medium containing both phenol (200 mg/liter) and glucose (0.15%) as carbon sources. The glucose consumption was not observed until the concentration of phenol decreased to around 10 mg/liter. This phenomenon was confirmed by [U-14C]glucose uptake experiments. The intracellular activities of hexokinase (EC 2.7.1.1) and catechol 1,2-oxygenase (EC 1.13.1.1) changed inversely when phenol was added during growth in the glucose medium.

Biological Transport, Active↗
PubMed1984

Evidence for isofunctional enzymes in the degradation of phenol, m- and p-toluate, and p-cresol via catechol meta-cleavage pathways in Alcaligenes eutrophus.

A study of the degradation of phenol, p-cresol, and m- and p-toluate by Alcaligenes eutrophus 345 has provided evidence that these compounds are metabolized via separate catechol meta-cleavage pathways. Analysis of the enzymes synthesized by wild-type and mutant strains and by strains cured of the plasmid pRA1000, which encodes m- and p-toluate degradation, indicated that two or more isofunctional enzymes mediated several steps in the pathway. The formation of three catechol 2,3-oxygenases and two 2-hydroxymuconic semialdehyde hydrolases was indicated from an examination of the ratio of the specific activities of these enzymes against various substrates. Evidence for two 2-hydroxymuconic semialdehyde dehydrogenases, two 4-oxalocrotonate isomerases and decarboxylases, and three 2-ketopent-4-enoate hydratases was derived from the induction of these enzymes under different growth conditions. Each activity was detected when the wild type was grown in the presence of m-toluate, but not when grown with phenol (except for a hydratase) or p-cresol, whereas in strains cured of pRA1000, growth with phenol or p-cresol, but not with m-toluate, induced these enzymes. Hydroxylation of phenol and p-cresol appears to be mediated by the same enzyme.

Alcaligenes↗
PubMed1980

Evidence of the directive effect of 17 beta-conjugate group on the enzymatic O-methylation of catechol estrogen.

Incubations of 2-hydroxyestradiol (I), 2-hydroxyestradiol 17 beta-sulfate (II), and 2-hydroxyestradiol 17 beta-glucuronide (III) with purified rat liver catechol O-methyltransferase were carried out at pH 7.2 in the presence of Mg2+ and (3H-Me)-S-adenosyl-L-methionine. The radioactive methylated products, 2-methoxyestradiol (IV) and 2-hydroxyestradiol-3-methyl ether (V), from each substrate were quantificanted by reverse isotope dilution method after their complete separation and acetylation. In the experiments of conjugated substrates, II and III, the analyses of the methylated products were done after their hydrolysis of 17 beta-conjugate groups with acid or beta-glucuronidase. The product ratios (2-methoxy/3-methoxy) of substrates I, II, and III, were 1:1, 4:1, and 45:1, respectively. These results are suggesting that 17 beta-conjugate groups of 2-hydroxyestradiol has directive effect on enzymatic O-methylation of estrogen catechols. Further, it is estimated that following process may be present in the estradiol metabolism in rat and/or humans: estradiol leads to estradiol 17 beta-conjugates leads to 2-hydroxyestradiol 17 beta-conjugates leads to 2-methoxyestradiol 17 beta-conjugates.

Animals↗
PubMed2006

Application of the nanogold-4,4'-bis(methanethiol)biphenyl modified gold electrode to the determination of tyrosinase-catechol reaction kinetics in acetonitrile.

The reactivity of tyrosinase adsorbed on nanogold bound with 4,4'-bis(methanethiol)biphenyl monolayer self-assembled on a gold disk with catechol in a dipolar aprotic solvent, acetonitrile (AN), was studied by cyclic voltammetric and amperometric methods. Tyrosinase exhibited characteristics of a Michaelis-Menten kinetic mechanism. The tyrosinase attached to the nanogold continued to react with substrates in AN even when the water content was lower than 0.01 w/w%. The apparent Michaelis-Menten constant K(m) of tyrosinase for catechol is 5.5 +/- 0.4 mM (n = 5).

Acetonitriles↗
PubMed1976

Effect of catechol-thiol conjugates on tyrosinase-dependent tyrosine hydroxylation.

1. The tyrosinase reaction in the presence of a thiol compound was studied using mushroom tyrosinase (EC 1.10.3.1) with regard to catechol-thiol conjugates. 2. Although tyrosine hydroxylation of tyrosinase was extremely decreased in the presence of a thiol compound, the inhibitory effect was removed by the addition of a pyrocatechol-cysteine conjugate, S-(2,3-dihydroxyphenyl) cysteine, which was not oxidized by the enzyme. 3. The pyrocatechol-cysteine conjugate was also able to shorten the lag period of tyrosinase-dependent tyrosine hydroxylation. 4. The sigmoidal reaction curve of tyrosine hydroxylation observed in the presence of sulfhydryl compounds was found to be caused by the catechol-thiol conjugates, the final products of the enzyme reaction, which counteract the inhibitory effect of sulfhydryl compounds. 5. The pyrocatechol-cysteine conjugate, on the other hand, was shown to cause the decrease of the reaction rate of the enzyme during incubation.

Basidiomycota↗
PubMed1999

Isolation and characterization of catechol 1,2-dioxygenases from Rhodococcus rhodnii strain 135 and Rhodococcus rhodochrous strain 89: comparison with analogous enzymes of the ordinary and modified ortho-cleavage pathways.

Catechol 1,2-dioxygenases of the ordinary ortho-cleavage pathway have been isolated from strains Rhodococcus rhodnii 135 and Rhodococcus rhodochrous 89 grown on phenol as the sole source of carbon and energy. The activities of the catechol 1,2-dioxygenases with 3- and 4-methylpyrocatechols were 1.3-1.5 times higher than those with pyrocatechol. The rate of oxidation of 3-chloropyrocatechol catalyzed by both enzymes was 20% of the rate of oxidation of unsubstituted pyrocatechol. The enzymes are homodimers composed of 37-kD subunits.

Catechol 1,2-Dioxygenase↗