Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CATECHOL”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2002

Catechol and hydroquinone have different redox properties responsible for their differential DNA-damaging ability.

We examined the redox properties of the "carcinogenic" catechol and the "noncarcinogenic" hydroquinone in relation to different DNA damaging activities and carcinogenicity using 32P-labeled DNA fragments obtained from the human genes. In the presence of endogenous NADH and Cu2+, catechol induces stronger DNA damage than hydroquinone, although the magnitudes of their DNA damaging activities were reversed in the absence of NADH. In both cases, DNA damage resulted from base modification at guanine and thymine residues in addition to strand breakage induced by Cu+ and H2O2, generated during the oxidation of catechol and hydroquinone into 1,2-benzoquinone and 1,4-benzoquinone, respectively. EPR and 1H NMR studies indicated that 1,2-benzoquinone is converted directly into catechol through a nonenzymatic two-electron reduction by NADH whereas 1,4-benzoquinone is reduced into hydroquinone through a semiquinone radical intermediate through two cycles of one-electron reduction. The reduction of 1,2-benzoquinone by NADH proceeds more rapidly than that of 1,4-benzoquinone. This study demonstrates that the rapid 1,2-benzoquinone two-electron reduction accelerates the redox reaction turnover between catechol and 1,2-benzoquinone, resulting in the enhancement of DNA damage. These results suggest that the differences in NADH-mediated redox properties of catechol and hydroquinone contribute to their different carcinogenicities.

Catechols↗
PubMed2006

DNA oxidative damage by terpene catechols as analogues of natural terpene quinone methide precursors in the presence of Cu(II) and/or NADH.

Natural terpene quinone methides (QM) and their derivatives have been investigated as therapeutics due to their broad antifungal, antibacterial, and antitumor activities. Recently, we reported that a terpene QM was formed from the catechol precursor through the disproportionation of Cu(II)/(I) redox cycle, and extensive DNA damage was observed throughout the oxidation process. In this paper, we investigate DNA damage with a series of terpene catechols as analogues of natural QM precursors and suggest that reactive oxygen species (ROS) are responsible for the observed DNA damage in the Cu(2+)-induced oxidation despite the stereo- and structural difference of these catechol or subsequent oxidation products. In addition, the presence of NADH significantly enhanced the extent of DNA damage by oxidation of these catechols. Especially with alkene catechols 6-7, the extent of DNA damage was independent of the concentration of catechols, implying that NADH enables the continuous production of ROS through the redox cycle of catechols/quinones.

Base Sequence↗
PubMed2004

Functional identification of the gene locus (ncg12319 and characterization of catechol 1,2-dioxygenase in Corynebacterium glutamicum.

Corynebacterium glutamicum assimilated phenol, benzoate, 4-hydroxybenzoate p-cresol and 3,4-dihydroxybenzoate. Ring cleavage was by catechol 1,2-dioxygenase when phenol or benzoate was used and by protocatechuate 3,4-dioxygenase when the others were used as substrate. The locus ncg12319 of its genome was cloned and expressed in Escherichia coli. Enzyme assays showed that ncg12319 encodes a catechol 1,2-dioxygenase. This catechol 1,2-dioxygenase was purified and accepted catechol, 3-, or 4-methylcatechols, but not chlorinated catechols, as substrates. The optimal temperature and pH for catechol cleavage catalyzed by the enzyme were 30 degrees C and 9, respectively, and the Km and Vmax were determined to be 4.24 micromol l(-1) and 3.7 micromol l(-1) min(-1) mg(-1) protein, respectively.

Amino Acid Sequence↗
PubMed1998

Purification and characterization of catechol 1,2-dioxygenase from Rhodococcus rhodochrous NCIMB 13259 and cloning and sequencing of its catA gene.

A method was developed for the purification of catechol 1, 2-dioxygenase from Rhodococcus rhodochrous NCIMB 13259 that had been grown in the presence of benzyl alcohol. The enzyme has very similar apparent Km (1-2 microM) and Vmax (13-19 units/mg of protein) values for the intradiol cleavage of catechol, 3-methylcatechol and 4-methylcatechol and it is optimally active at pH9. Cross-linking studies indicate that the enzyme is a homodimer. It contains 0.6 atoms of Fe per subunit. The enzyme was crystallized with 15% (w/v) poly(ethylene glycol) 4000/0.33 M CaCl2/25 mM Tris (pH7.5) by using a microseeding technique. Preliminary X-ray characterization showed that the crystals are in space group C2 with unit-cell dimensions a=111.9 A, b=78.1 A, c=134.6 A, beta=100 degrees. An oligonucleotide probe, made by hemi-nested PCR, was used to clone the gene encoding catechol 1,2-dioxygenase (catA). The deduced 282-residue sequence corresponds to a protein of molecular mass 31539 Da, close to the molecular mass of 31558 Da obtained by electrospray MS of the purified enzyme. catA was subcloned into the expression vector pTB361, allowing the production of catechol 1,2-dioxygenase to approx. 40% of the total cellular protein. The deduced amino acid sequence of the enzyme has 56% and 75% identity with the catechol 1, 2-dioxygenases of Arthrobacter mA3 and Rhodococcus erythropolis AN-13 respectively, but less than 35% identity with intradiol catechol and chlorocatechol dioxygenases of Gram-negative bacteria.

Amino Acid Sequence↗
PubMed2005

A novel mechanism for adenylyl cyclase inhibition from the crystal structure of its complex with catechol estrogen.

Catechol estrogens are steroid metabolites that elicit physiological responses through binding to a variety of cellular targets. We show here that catechol estrogens directly inhibit soluble adenylyl cyclases and the abundant trans-membrane adenylyl cyclases. Catechol estrogen inhibition is non-competitive with respect to the substrate ATP, and we solved the crystal structure of a catechol estrogen bound to a soluble adenylyl cyclase from Spirulina platensis in complex with a substrate analog. The catechol estrogen is bound to a newly identified, conserved hydrophobic patch near the active center but distinct from the ATP-binding cleft. Inhibitor binding leads to a chelating interaction between the catechol estrogen hydroxyl groups and the catalytic magnesium ion, distorting the active site and trapping the enzyme substrate complex in a non-productive conformation. This novel inhibition mechanism likely applies to other adenylyl cyclase inhibitors, and the identified ligand-binding site has important implications for the development of specific adenylyl cyclase inhibitors.

Adenosine Triphosphate↗
PubMed1989

Variations in catechol O-methyltransferase activity in rodent tissues: possible role in estrogen carcinogenicity.

Catechol-O-methyltransferase (COMT) [EC 2.1.1.6] is a ubiquitous cytosolic enzyme which has a pertinent role in the inactivation of both natural and synthetic catechol estrogens in mammalian tissues. We have compared the COMT activity in mouse, hamster and rat kidney, liver and red blood cells and examined the kinetic characteristics of this enzyme in the latter two species using various catechol estrogens as substrates. Results presented here indicate that the ratios of COMT activity in the kidney versus the liver of the rat and mouse are nearly identical, 0.48-0.52, whereas there is a 29-fold ratio between the level of COMT activity in these two tissues in the hamster. In red blood cells, the level of COMT activity is 4- and 12-fold lower in the hamster compared to mouse and rat, respectively. When the kinetic characteristics of this enzyme were assessed in the hamster and rat kidney and liver, except for 2-hydroxymoxestrol which had an apparent Km value of 15-48 microM, the other catechol estrogen substrates exhibited Km values ranging from 1-10 microM. Generally, the Vmax values were markedly higher in the rat kidney and liver than those observed in corresponding hamster tissues. The significantly lower COMT activity in the hamster liver and red blood cells suggests that under chronic estrogen treatment at high doses, the concentration of catechol estrogens in these tissues may exceed the capacity of COMT to effectively catalyse their O-methylation into inactive metabolites. The resulting accumulation of catechol estrogens may contribute to the estrogen carcinogenicity observed in the hamster liver and kidney. Additionally, when 2-hydroxyestrone was used as a substrate, the estrogen-induced renal carcinoma exhibited only 8.6% of the COMT activity found in the normal kidney.

Animals↗
PubMed1989

Effects of catechol on the induction of tumors in mouse skin by 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrenes.

Catechol (1,2-dihydroxybenzene) is a major phenolic compound present in the co-carcinogenic fraction of cigarette tar. It has been shown to be a potent co-carcinogen with benzo[a]pyrene (BaP) in mouse skin. In this study we have examined the co-carcinogenic and co-initiating activities of catechol with racemic and enantiomeric 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrenes (BaP-7,8-diols) in mouse skin. Similar to enhancement of BaP carcinogenesis, repeated concurrent applications of catechol and (+/-)-BaP-7,8-diol to mouse skin strongly enhanced (+/-)-BaP-7,8-diol tumor multiplicity and tumor incidence, and decreased latency. Co-application of catechol with the racemic or either of the enantiomers of BaP-7,8-diol in a two-stage initiation--promotion protocol increased the tumor initiating activity of racemic BaP-7,8-diol, similar to that of BaP, by approximately 50%, but had no statistically significant effect on the tumor initiating activity of the (+)- or (-)-enantiomers in mouse skin. Thus, catechol is as potent a co-carcinogen with (+/-)-BaP-7,8-diol as it is with BaP. However, as tested here catechol is a weak co-initiator when applied with (+/-)-BaP-7,8-diol or BaP.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2005

Association study of catechol-O-methyltransferase gene polymorphism in Korean male alcoholics.

OBJECTIVE: Catechol-O-methyltransferase, which has a functional genetic polymorphism, plays an important role in dopamine metabolism. The study analyzed the association between the catechol-O-methyltransferase gene polymorphism and alcohol dependence in the Korean population. METHODS: Ninety-seven male alcoholics and 94 male age-matched normal controls were enrolled in this study. Polymerase chain reaction-based genotyping was used to verify the presence of the catechol-O-methyltransferase gene polymorphism. The patients were divided into two subtypes (violent group and non-violent group) according to their history of violent behavior. RESULTS: No difference in the distribution of the catechol-O-methyltransferase genotypes (H/H, H/L, L/L) and alleles (H, L) was observed between the patients and the controls. However, the differences between the violent and non-violent groups were significant in terms of the frequencies of the COMT genotypes (chi=7.977, df=2, P=0.019) and the alleles (chi=6.832, df=1, P=0.012). In addition, significant differences in the frequencies of the catechol-O-methyltransferase allele (chi=4.481, df=1, P=0.040) were observed between the non-violent group and the controls. CONCLUSIONS: This suggests that the catechol-O-methyltransferase gene polymorphism is not associated with the development of alcohol dependence, but may affect the susceptibility to a clinical heterogeneity of alcohol dependence, at least in the Korean population.

Alcoholism↗
PubMed2000

Dual regulation of catecholate siderophore biosynthesis in Azotobacter vinelandii by iron and oxidative stress.

Azotobacter vinelandii forms both catecholate and azotobactin siderophores during iron-limited growth. Azotobactin is repressed by about 3 microM iron, but catecholate siderophore synthesis continues up to a maximum of 10 microM iron. This suggests that catecholate siderophore synthesis is regulated by other factors in addition to the ferric uptake repressor (Fur). In this study the first gene required for catecholate siderophore biosynthesis, which encodes an isochorismate synthase (csbC), was isolated. The region upstream of csbC contained a typical sigma(70) promoter, with an iron-box overlapping the -35 sequence and a Sox-box (Box 1) overlapping the -10 sequence. Another Sox-box was found further upstream of the -35 sequence (Box 2). Also upstream, an unidentified gene (orfA) was detected which would be transcribed from a divergent promoter, also controlled by an iron-box. The activity of csbC and a csbC::luxAB fusion was negatively regulated by iron availability and upregulated by increased aeration and by superoxide stress. The iron-box in the csbC promoter was 74% identical to the Fur-binding consensus sequence and bound the Fur protein of Escherichia coli with relatively high affinity. Both Box 1 and Box 2 were in good agreement with the consensus sequence for binding the SoxS protein of E. coli and Box 1 was in very good agreement with the Sox-box found in the fpr promoter of A. vinelandii, which is also regulated by superoxide stress. Both Sox-boxes bound a protein found in A. vinelandii cell extracts, with Box 1 exhibiting the higher binding affinity. The Sox protein identified in this assay appeared to be constitutive, rather than inducible by superoxide stress. This indicates that the Sox response in A. vinelandii is different from that in E. coli. These data support the hypothesis that catecholate siderophore biosynthesis is under dual control, repressed by a Fur-iron complex and activated by another DNA-binding protein in response to superoxide stress. The interaction between these regulators is likely to account for the delay in ferric repression of catecholate siderophore production, since these siderophores have an additional role to play in the protection of iron-limited cells against oxidative damage.

Amino Acid Sequence↗
PubMed1994

Anaerobic degradation of catechol by Desulfobacterium sp. strain Cat2 proceeds via carboxylation to protocatechuate.

Under anoxic conditions, most methoxylated mononuclear aromatic compounds are degraded by bacteria, with catechol being formed as an important intermediate. On the basis of our experiments with the sulfate-reducing bacterium Desulfobacterium sp. strain Cat2, we describe for the first time the enzymatic activities involved in the complete anaerobic oxidation of catechol and protocatechuate. Results obtained from experiments with dense cell suspensions of strain Cat2 demonstrated that all enzymes necessary for protocatechuate and benzoate degradation were induced during growth with catechol. In addition, anaerobic oxidation of catechol was found to be a CO2-dependent process. Phenol was not degraded in suspensions of cells grown with catechol. In cell extracts of Desulfobacterium sp. strain Cat2, protocatechuyl-coenzyme A (CoA) was formed from catechol, bicarbonate, and uncombined CoA. This oxygen-sensitive reaction requires high concentrations of both bicarbonate and protein, and only very low levels of enzyme were detected. In a second oxygen-sensitive step, protocatechuyl-CoA was reduced to 3-hydroxybenzoyl-CoA by reductive elimination of the p-hydroxyl group. Further dehydroxylation to benzoyl-CoA was not detectable. Key reactions described for anaerobic degradation of benzoate were catalyzed by cell extracts of strain Cat2, too.

Anaerobiosis↗
PubMed2000

Development of catechol 2,3-dioxygenase-specific primers for monitoring bioremediation by competitive quantitative PCR.

Benzene, toluene, xylenes, phenol, naphthalene, and biphenyl are among a group of compounds that have at least one reported pathway for biodegradation involving catechol 2,3-dioxygenase enzymes. Thus, detection of the corresponding catechol 2,3-dioxygenase genes can serve as a basis for identifying and quantifying bacteria that have these catabolic abilities. Primers that can successfully amplify a 238-bp catechol 2,3-dioxygenase gene fragment from eight different bacteria are described. The identities of the amplicons were confirmed by hybridization with a 238-bp catechol 2,3-dioxygenase probe. The detection limit was 10(2) to 10(3) gene copies, which was lowered to 10(0) to 10(1) gene copies by hybridization. Using the dioxygenase-specific primers, an increase in catechol 2, 3-dioxygenase genes was detected in petroleum-amended soils. The dioxygenase genes were enumerated by competitive quantitative PCR with a 163-bp competitor that was amplified using the same primers. Target and competitor sequences had identical amplification kinetics. Potential PCR inhibitors that could coextract with DNA, nonamplifying DNA, soil factors (humics), and soil pollutants (toluene) did not impact enumeration. Therefore, this technique can be used to accurately and reproducibly quantify catechol 2, 3-dioxygenase genes in complex environments such as petroleum-contaminated soil. Direct, non-cultivation-based molecular techniques for detecting and enumerating microbial pollutant-biodegrading genes in environmental samples are powerful tools for monitoring bioremediation and developing field evidence in support of natural attenuation.

Biodegradation, Environmental↗
PubMed1998

Catechol activation in rat rostral ventrolateral medulla after systemic isocapnic metabolic acidosis.

The catechol signal recorded using in vivo voltammetry within the rat rostral ventrolateral medulla (RVLM) can be interpreted as a catechol-specific index of the integrated activity of RVLM adrenergic barosensitive bulbospinal and nonbulbospinal neurons. To test the hypothesis that systemic acidosis leads to the activation of RVLM adrenergic neurons, the RVLM catechol signal was observed in rats after mild systemic acidosis (pH 7.20-7.25 for 30 min) induced by 1 M HCl under halothane anesthesia, controlled mechanical ventilation, and continuous infusion of Ringer lactate. Particular attention was paid to ensure that changes in mean arterial pressure (MAP) were <15 mmHg during HCl challenge. Saline administration was not associated with any significant change in all considered variables (n = 5). Mild isocapnic systemic acidosis was associated with an increase in catechol signal (n = 5), irrespective of carotid sinus nerve section (n = 5). In keeping with the aim of the study, there were minor (<15 mmHg) but significant changes in MAP among saline, intact, and deafferented groups. Changes in heart rate were not significant. In conclusion, a catechol activation is observed in the RVLM when arterial pressure is maintained during isocapnic systemic metabolic acidosis. This catechol activation appears primarily centrally mediated. Therefore, adrenergic RVLM neurons may relay inputs from the central respiratory generator to the sympathetic system and/or act as chemosensors for H+ next to the surface of the ventrolateral medulla.

Acidosis↗
PubMed2005

Catechol inhibits FADH2-linked respiration in rat liver mitochondrial fraction.

PURPOSE: The aim of this work was to investigate the hypothesis that catechol inhibits FADH -linked basal respiration in mitochondria isolated from rat liver homogenates. Moreover, catechol ability to induce peroxidation of biomolecules in liver nuclear fractions was also studied. METHODS: Rat liver homogenates were incubated with 1mM 1,2-dihydroxybenzene (catechol) at pH 7.4 for up to 30 minutes. After that, mitochondrial fractions were isolated by differential centrifugation. Basal oxygen uptake was measured using a Clark-type electrode after the addition of 10 mM sodium succinate. Nuclear fractions were incubated in the presence of 1 mM catechol for 17 hours at room temperature and the peroxidation of biomolecules was investigated by the reaction with thiobarbituric acid, which was determined spectrophotometrically at 535 nm. RESULTS: Catechol induced a time-dependent partial inhibition of FADH -linked basal mitochondrial respiration, however this substance was unable to induce a direct peroxidation of biomolecules in hepatic nuclear fractions. CONCLUSION: Catechol produced an inhibition of basal respiration associated to FADH2 in isolated liver mitochondria that could lead to cytotoxicity, ROS generation and cell death.

Animals↗
PubMed1992

Reversibility of catechol-induced rat glandular stomach lesions.

The potential reversibility of glandular stomach lesions induced by the clastogen, catechol, was examined in groups of male F344 rats treated continuously with 0.8% catechol in the diet for 12, 24, 48, 72, or 96 weeks. After a return to basal diet for 84, 72, 48, 24, and 0 weeks, respectively, the animals were killed for histopathological examination. Incidences of submucosal hyperplasia, adenomas and adenocarcinomas, average number of tumors per rat, and the size of tumors in rats treated with catechol for 12, 24, 48, 72, and 96 weeks increased time dependently. After cessation of catechol treatment, although average number of tumors per rat slightly decreased, the size of tumors tended to increase. Labeling indices in both tumorous and nontumorous areas decreased after cessation of catechol treatment. The results thus indicate that whereas some submucosal hyperplasias or adenomas may regress, others have the potential to develop into adenomas or adenocarcinomas. However, tumor growth does depend to a certain extent on continued catechol treatment.

Adenocarcinoma↗
PubMed1989

Modification by catechol and resorcinol of upper digestive tract carcinogenesis in rats treated with methyl-N-amylnitrosamine.

Modifying effects of the environmental contaminant catechol, and its isomers resorcinol and hydroquinone, on methyl-N-amylnitrosamine (MNAN)-induced carcinogenesis were studied in male F344 rats. Groups of 15 rats were given three i.p. injections of 25 mg/kg of body weight of MNAN within the initial 2-wk period, and commencing 1 wk thereafter they were administered 0.8% catechol, 0.8% resorcinol, or 0.8% hydroquinone in powdered basal diet or were given basal diet alone for 49 wk. Additional groups of 10 to 15 rats were similarly treated without prior carcinogen exposure. Histological examination after sacrifice at wk 52 revealed that the incidences of tongue papillomas and esophageal squamous cell carcinomas in the groups given MNAN followed by catechol (57.1% and 64.3%) or resorcinol (50% and 58.8%) were significantly higher than those in the carcinogen only controls (9.1, and 0%, respectively). Hydroquinone also enhanced the development of esophageal squamous cell carcinomas but was less active than catechol or resorcinol. The incidence of alveolar hyperplasia in the lungs of the group given MNAN followed by catechol (0%) was, in contrast, significantly reduced as compared to the control value (54.5%). Hydroquinone and resorcinol showed a similar but non-significant tendency. These results indicated that the environmental contaminant, catechol and its isomers, may play a role in the development of human upper gastrointestinal cancer, in addition to exerting modifying effects in other organs.

Animals↗
PubMed1985

Estrogen 2- and 4-hydroxylase activity, catechol estrogen formation, and implications for estrogen carcinogenesis in the hamster kidney.

Estrogen 2- and 4-hydroxylase (ESH), a microsomal enzyme which mediates the formation of catechol estrogens, has been studied in the kidneys of castrated male Syrian hamsters, a species uniquely susceptible to induction of renal carcinomas by both steroidal and stilbene estrogens. The apparent Km for estrone was 17.0 microM, and Vmax was 0.5 pmol per mg protein per min for ESH in renal microsomes derived from castrated hamsters. Different steroidal estrogen substrates exhibited decreasing catechol formation with hamster kidney microsomal preparations in the following order: estrone greater than d-equilenin greater than 17 beta-estradiol greater than equilin greater than ethynyl estradiol greater than estriol. Except for beta-dienestrol, the stilbene estrogens revealed levels of catechol formation that were similar to 17 beta-estradiol. These findings provide a rationale for the weak carcinogenic activity of ethynyl estradiol, estriol, and beta-dienestrol, since they were poor substrates for hamster renal ESH and for the relatively potent carcinogenic activity of the distal metabolite of diethylstilbestrol, indenestrol B/A, which exhibited substantial levels of o-hydroxylation when used as a substrate. Interestingly, ESH activity was significantly greater in the hamster kidney compared to corresponding rat tissue, and catechol estrogen formation was found to be 2.5- to 19-fold higher in the hamster kidney compared to the rat, using various steroidal and stilbene estrogen substrates. Moreover, the finding that a 3.5- to nearly 6-fold decrease, compared to untreated levels, in catechol formation in kidneys but not in livers of alpha-naphthoflavone-exposed hamsters, depending on the steroidal or stilbene estrogen substrate used, is consistent with the belief that the catechol estrogen pathway is pertinent to events leading to estrogen-induced renal tumorigenesis in the hamster.

Animals↗
PubMed1985

Test of catechol, tannic acid, Bidens pilosa, croton oil, and phorbol for cocarcinogenesis of esophageal tumors induced in rats by methyl-n-amylnitrosamine.

Catechol (CAS: 120-80-9), given in drinking water to rats, was the most effective of 5 phenols in enhancing [3H]thymidine incorporation [( 3H]dThd-l) into esophageal DNA. To test for esophageal cocarcinogenesis, groups of 30 male MRC-Wistar rats received 3 weekly ip injections of 25 mg methyl-n-amylnitrosamine [(MNAN) CAS: 13256-07-0]/kg. From the time of the first MNAN injection, each group also received catechol, tannic acid (CAS: 1401-55-4), dried leaves of Bidens pilosa L., or croton oil (CAS: 8001-28-3) (respectively, 2, 10, 50, and 2 g/kg semipurified diet), or were given 20 ip injections of 6 mg phorbol (CAS: 17673-25-5)/rat. The rats were killed after 20-45, 46-52, or 53-72 weeks (subgroups A, B, and C). In the group given MNAN alone, most esophageal papillomas developed during the first 45 weeks. Both catechol and B. pilosa significantly increased the esophageal papilloma multiplicity (No. of papillomas/rat) induced by MNAN, with a maximum tumor yield of 2.2 times that in the corresponding subgroup treated with MNAN alone. Papilloma multiplicity increased from subgroup A to subgroup C in the MNAN plus B. pilosa group but not in the MNAN plus catechol group. No tumors were induced by the test cocarcinogens given without MNAN. We concluded that a) an increased esophageal [3H]dThd-I indicates potential cocarcinogenicity and b) catechol and B. pilosa were weak esophageal cocarcinogens. These results support the view that catechol in cigarette smoke and B. pilosa as eaten in South Africa contribute to the etiology of human esophageal cancer.

Animals↗
PubMed1984

An electron spin resonance study of o-semiquinones formed during the enzymatic and autoxidation of catechol estrogens.

Electron spin resonance spectroscopy has been used to demonstrate production of semiquinone-free radicals from the oxidation of the catechol estrogens 2- and 4-hydroxyestradiol and 2,6- and 4,6-dihydroxyestradiol. Radicals were generated either enzymatically (using horseradish peroxidase-H2O2 or tyrosinase-O2) or by autoxidation, and were detected as their complexes with spin-stabilizing metal ions (Zn2+ and/or Mg2+). In the peroxidase system, radicals are produced by one-electron oxidation of the catechol estrogen and their decay is by a second-order pathway, consistent with their disproportionation to quinone and catechol products. With tyrosinase-O2, radical generation occurs indirectly. Initial hydroxylation of phenolic estrogen (at either the 2- or 4-position) gives a catechol estrogen in situ; subsequent two-electron oxidation of the catechol to the quinone, followed by reverse disproportionation, leads to the formation of radicals. A competing mechanism for radical production involves autoxidation of the catechol. Results obtained from the estrogen systems have been compared with those from the model compound 5,6,7,8-tetrahydro-2-naphthol.

Benzoquinones↗