Differential effect of schisandrin B and dimethyl diphenyl bicarboxylate (DDB) on hepatic mitochondrial glutathione redox status in carbon tetrachloride intoxicated mice

The effects of schisandrin B (Sch B), a dibenzocyclooctadiene derivative isolated from the fruit of Schisandra chinensis, and dimethyl diphenyl bicarboxylate (DDB), a synthetic intermediate of schisandrin C (also a dibenzocyclooctadiene derivative), on hepatic mitochondrial glutathione redox status in control and carbon tetrachloride (CCl4)-intoxicated mice were examined. Treating mice with Sch B or DDB at a daily oral dose of 1 mmol/kg for 3 d did not produce any significant alterations in plasma alanine aminotransferase (ALT) and sorbital dehydrogenase (SDH) activities. CCl4 treatment caused drastic increases in both plasma ALT and SDH activities in mice. Pretreating mice with Sch B or DDB at the same dosage regimen significantly suppressed the CCl4-induced increase in plasma ALT activity, with the inhibitory effect of Sch B being much more potent. Sch B, but not DDB, pretreatment could also decrease the plasma SDH activity in CCl4-intoxicated mice. The lowering of plasma SDH activity, indicative of hepatoprotection against CCl4 toxicity, by Sch B pretreatment was associated with an enhancement in hepatic mitochondrial glutathione redox status as well as an increase in mitochondrial glutathione reductase (mtGRD) activity in both non-CCl4 and CCl4-treated mice. DDB pretreatment, though enhancing both hepatic mitochondrial glutathione redox status and mtGRD activity in control animals, did not produce any beneficial effect in CCl4-treated mice. The difference in hepatoprotective action against CCl4 toxicity between Sch B and DDB may therefore be related to their ability to maintain hepatic mitochondrial glutathione redox status under oxidative stress condition.

A comparison of the ability of forest and agricultural soils to mineralize chlorinated aromatic compounds

Soils were sampled from two agricultural fields, two relatively pristine forests, and one suburban forest in Ontario, Canada. The ability of these soils to mineralize 2,4-dichlorophenoxyacetate, 3-chlorobenzoate, 4-chlorophenol, 2,4-dichlorophenol, pentachlorophenol, and atrazine was determined using 14C-labeled substrates. Direct pre-exposure was necessary before atrazine mineralization could be detected; however, it was not necessary for degradation of any of the other chemicals. 2,4-dichlorophenoxyacetate and pentachlorophenol mineralization was much higher in the agricultural soils relative to the pristine forest soils, but 3-chlorobenzoate and 2,4-dichlorophenol mineralization rates showed the opposite trend. Mineralization of 4-chlorophenol was about equivalent in all soils. Suburban forests soils were indistinguishable from agricultural soils with respect to their degradation of 2,4-dichlorophenoxyacetate and chlorobenzoate. Additionally, they were better able than any of the soils to withstand the toxic effects of pentachlorophenol. Pentachlorophenol mineralization was highly variable in the pristine forest soils, ranging from about 6 to 50%. Abiotic factors such as pH, soil type, and organic and moisture content did not account for these significant site differences. The selective forces responsible for these differences, and the possible differences in microbial populations are discussed.

Human neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes predict efficacy of halogenated compounds that disobey the Meyer-Overton rule

BACKGROUND

According to the Meyer-Overton rule, anesthetic potency of a substance can be predicted by its lipid solubility, but a group of halogenated volatile compounds predicted to induce anesthesia does not obey this rule. Thus, these compounds are useful tools for studies of molecular targets of anesthetics. Human neuronal nicotinic acetylcholine receptor (hnAChR) subunits have been recently cloned, which allowed the authors to assess whether these receptors could differentiate among volatile anesthetic and nonimmobilizer compounds. This study provides the first data regarding anesthetic sensitivity of hnAChRs.

METHODS

alpha2beta4, alpha3beta4, and alphaabeta2 hnAChRs were expressed in Xenopus oocytes, and effects of volatile anesthetics isoflurane and F3 (1-chioro-1,2,2-triflurocyclobutane, 1A) and nonimmobilizers F6 (1,2-dichlorohexafluorocyclobutane, 2N) and F8 (2,3-dichlorooctafluorobutane) on the peak acetylcholine-gated currents were studied using the two-electrode voltage-clamp technique.

RESULTS

Isoflurane and F3 inhibited all the hnAChRs tested in a concentration-dependent manner. Isoflurane at a concentration corresponding to 1 minimum alveolar concentration (MAC) inhibited 83, 69, and 71% of ACh-induced currents in alpha2beta4, alpha3beta4, and alpha4beta2 hnAChRs, respectively, and 1 MAC of F3 inhibited 64, 44, and 61% of currents gated in those receptors. F6 (8-34 microM) did not cause any changes in currents gated by any of the receptors tested. F8 (4-18 microM) did not alter the currents gated in either alpha3beta4 or alpha4beta2 receptors, but caused a small potentiation of alpha2beta4 hnAChRs without a concentration-response relation.

CONCLUSION

The in vivo potency and effectiveness of volatile anesthetic and nonimmobilizer compounds were consistent with their actions on hnAChRs expressed in a recombinant expression system, suggesting a potential participation of these receptors in the mechanisms of anesthesia.

Performance evaluation of a permeable reactive barrier for remediation of dissolved chlorinated solvents in groundwater

A pilot-scale permeable reactive barrier (PRB) consisting of granular iron was installed in May 1995 at an industrial facility in New York to evaluate the use of this technology for remediation of chlorinated volatile organic compounds (VOCs) in groundwater. The performance of the barrier was monitored over a 2-year period. Groundwater velocity through the barrier was determined using water level measurements, tracer tests, and in situ velocity measurements. While uncertainty in the measured groundwater velocity hampered interpretation of results, the VOC concentration data from wells in the PRB indicated that VOC degradation rates were similar to those anticipated from laboratory results. Groundwater and core analyses indicated that formation of carbonate precipitates occurred in the upgradient section of the iron zone, however, these precipitates did not appear to adversely affect system performance. There was no indication of microbial fouling of the system over the monitoring period. Based on the observed performance of the pilot, a full-scale iron PRB was installed at the site in December 1997.

Long-term performance monitoring for a permeable reactive barrier at the U.S. Coast Guard Support Center, Elizabeth City, North Carolina

A continuous hanging iron wall was installed in June, 1996, at the U. S. Coast Guard (USCG) Support Center near Elizabeth City, NC, United States, to treat overlapping plumes of chromate and chlorinated solvent compounds. The wall was emplaced using a continuous trenching machine whereby native soil and aquifer sediment was removed and the iron simultaneously emplaced in one continuous excavation and fill operation. To date, there have been seven rounds (November 1996, March 1997, June 1997, September 1997, December 1997, March 1998, and June 1998) of performance monitoring of the wall. At this time, this is the only full-scale continuous 'hanging' wall installed as a permeable reactive barrier to remediate both chlorinated solvent compounds and chromate in groundwater. Performance monitoring entails the following: sampling of 10-5 cm PVC compliance wells and 15 multi-level samplers for the following constituents: TCE, cis-dichloroethylene (c-DCE), vinyl chloride, ethane, ethene, acetylene, methane, major anions, metals, Cr(VI), Fe(II), total sulfides, dissolved H(2), Eh, pH, dissolved oxygen, specific conductance, alkalinity, and turbidity. Electrical conductivity profiles have been conducted using a Geoprobe to verify emplacement of the continuous wall as designed and to locate upgradient and downgradient wall interfaces for coring purposes. Coring has been conducted in November, 1996, in June and September, 1997, and March, 1998, to evaluate the rate of corrosion on the iron surfaces, precipitate buildup (particularly at the upgradient interface), and permeability changes due to wall emplacement. In addition to several continuous vertical cores, angled cores through the 0.6-m thick wall have been collected to capture upgradient and downgradient wall interfaces along approximate horizontal flow paths for mineralogic analyses.

Results of the reactant sand-fracking pilot test and implications for the in situ remediation of chlorinated VOCs and metals in deep and fractured bedrock aquifers

Permeable reactive barriers (PRBs), such as the Waterloo Funnel and Gate System, first implemented at Canadian Forces Borden facility in 1992, are a passive remediation technology capable of controlling the migration of, and treating contaminated groundwater in situ. Most of the PRBs installed to date have been shallow installations created by backfilling sheet-pile shored excavations with iron filing reactive media. More recently continuous trenchers [R. Puls, Installation of permeable reactive barriers using continuous trenching equipment, Proceedings of the RTDF Permeable Barriers Work Group, Virginia Beach, VA, September 1997] and Caissons [J. Vogan, Caisson installation of a pilot scale, permeable reactive barrier in situ treatment zone at the Sommersworth Landfill, NH, Presented to the RTDF Permeable Barriers Work Group, Alexandria, VA, April 1996], and vertical fracturing emplacements [G. Hocking, Vertical hydraulic fracture emplacement of permeable reactive barriers, Progress Report delivered to the Permeable Reactive Barriers Workgroup of the Remedial Technology Development Forum, Beaverton, OR, April 1998] have been used to create reactive barriers in soil. None of the prior methods are capable of adequately addressing groundwater contamination in deep and fractured bedrock aquifers. The purpose of the RSF pilot study was to install reactive media into an impacted bedrock aquifer, and to evaluate the effectiveness of in situ treatment of chlorinated volatile organic compounds (CVOCs) and metals in that type of aquifer. Three discrete fractures were identified and treated and were subjected to testing before and after treatment. Between 300 and 1700 lb. of 1 mm diameter reactive proppants were injected into each zone to facilitate treatment. Monitoring data obtained from adjacent observation wells verified that fracking fluids reached at least 42 ft from the treatment well following hydrofracturing. The concentrations of many of the CVOCs decreased up to 98% based on the results of pre- and post-RSF treatment analyses. Consistent with other research, concentrations of CVOCs were noted to decrease including trichloroethene (TCE), tetrachloroethene (PCE), 1,1,1-trichloroethane (1,1,1-TCA), 1, 1-dichloroethane (1,1-DCA), and 1,1-dichloroethene (1,1-DCE) and increases were noted in concentrations of cis-1,2-dichloroethene (cis-1,2-DCE) and chloroform suggesting that the rate of transformation of the parent compounds to these daughter products is higher than the rate of destruction of the daughter products. The RSF pilot study demonstrated that: (1) zero valent iron foam proppants have the physical and chemical properties necessary to effectively treat CVOCs and metals in groundwater when inserted under high pressures into fractured bedrock. (2) Iron foam reactive media can be placed in bedrock using high pressure hydraulic fracturing equipment and polysaccharide viscosifiers. (3) The extent of the treatment can be monitored in situ using tracers and pressure transducers. (4) Well capacity is increased by improving hydraulic conductivity through hydraulic fracturing and proppant injection. The approximate cost of all of the effort expended in the pilot study was about US$200,000. Full-scale implementations are projected to cost between US$100,000 and US$1,000,000 and would depend on site specific conditions such as the extent and level of impacted groundwater requiring treatment. This technology can potentially be implemented to create treatment zones for the passive treatment of CVOC and metal impacted groundwater in fractured rock aquifers offering a cost-effective alternative to a pump and treat forever scenario.

Interaction of hydroxycinnamic acid derivatives with the Cl3COO radical: a pulse radiolysis study

The electron transfer reactions between the trichloromethylperoxyl radical (Cl3COO*) and hydroxycinnamic acid derivatives, including chlorogenic acid, sinapic acid, caffeic acid, ferulic acid and 3,4-(methylenedioxy)cinnamic acid, have been studied by pulse radiolysis. The hydroxycinnamic acid derivatives, especially sinapic acid, are identified as good antioxidants for reduction of Cl3COO* via electron transfer reactions. From buildup kinetic analysis of phenoxyl radical, the rate constant for reaction of Cl3COO* with sinapic acid has been determined to be 8.2x10(7) dm3 mol(-1) s(-1), while the rate constants of electron transfer from other hydroxycinnamic acid derivatives to Cl3COO* were obtained to be about 2x10(7) dm3 mol(-1) s(-1). The reaction of 3,4-(methylenedioxy) cinnamic acid with Cl3COO* was investigated as an evidence for the electron transfer mechanism.

Discrimination of structural isomers of chlorinated phenols in waters using gas chromatography-mass spectrometry in the negative chemical ionization mode

The analysis and identification of structural isomers of mono-, di- and trichlorophenols is reported. The fragmentation of the phenols was examined by GC-MS in both electron impact (EI) and negative chemical ionization (NCI) modes, using methane as reagent gas. The ability of NCI to discriminate these isomeric compounds from differences in relative intensities for selected peaks is demonstrated. 3- and 4-chlorophenols have similar retention times; however, they can still be discriminated because their negative mass spectra and rather different. In dichlorophenols, the presence of one chlorine atom in the ortho position decreases their retention time and the relative intensity of the fragment ion at m/z 140. The NCI mass spectra for trichlorophenols are different from the rest, particularly for the m/z value corresponding to the chlorine atom. Tetra- and pentachlorophenols were also studied and sequential losses of Cl observed. An automatic solid-phase extraction system can optionally be used to preconcentrate chlorophenols in waters prior to determination at legally established toxic levels.

Generation of antibodies to Di- and trichloroacetylated proteins and immunochemical detection of protein adducts in rats treated with perchloroethene

Antibodies directed against chemical specific protein modifications are valuable tools to detect and comparatively quantify protein modifications. Both Nepsilon-(dichloroacetyl)-L-lysine and Nepsilon-(trichloroacety)l-L-lysine have been detected as modified amino acids in liver and kidneys of rats treated with perchloroethene (PER) after proteolysis. These protein modifications are formed by the interaction of reactive metabolites formed from PER with proteins. In this study we developed monospecific antibodies to dichloroacetylated and to trichloroacetylated amino acids to detect modified proteins in the target organs of PER toxicity. These antibodies were prepared by immunization of rabbits with modified keyhole limpet hemocyanin (KLH) coupled with either the dichloroacetyl or trichloroacetyl moiety. Enzyme-linked immunosorbent assays (ELISA) indicated that the polyclonal rabbit sera recognized dichloroacetylated or trichloroacetylated rabbit serum albumin (RSA), but not unmodified protein. Therefore, we further purified rabbit antisera on either Nepsilon-(dichloroacetyl)-L-lysine or Nepsilon-(trichloroacetyl)-L-lysine immobilized to immunoaffinity columns to obtain monospecific antibodies. The potential of these antibodies in the detection of di- and trichloroacetylated proteins and their selectivity for the desired dichloroacetyl or trichloroacetyl group was demonstrated in competitive enzme-linked immunosorbent assays with several structurally related compounds. Anti-dichloroacetyl (anti-DCA) antibody binding to dichloroacetylated RSA was inhibited by Nepsilon-(dichloroacetyl)-L-lysine with an IC50 value of 150 microM whereas inhibition by Nepsilon-(monochloroacetyl)-L-lysine and Nepsilon-(trichloroacetyl)-L-lysine showed an IC50 value of 100 mM. The binding of the anti-trichloroacetyl (anti-TCA) antibody to trichloroacetylated RSA was inhibited by Nepsilon-(dichloroacetyl)-L-lysine with an IC50 value of 80 mM. The inhibition by Nepsilon-(trichloroacetyl)-L-lysine was again 3 orders of magnitude stronger resulting in an IC50 value of 90 microM. Nepsilon-(acetyl)-L-lysine and unmodified RSA did not effect antibody binding to the chemically modified antigen. The antibodies were also successfully applied to detect modified proteins in subcellular fractions of liver and kidney from PER treated rats demonstrated in immunoblot. Protein adduct formation from different PER metabolism pathways was confirmed by the observation that the majority of dichloroacetylated proteins were located in kidney mitochondria and trichloroacetylated proteins were located in liver microsomes.

Aminated polysaccharides as bile acid sorbents: in vitro study

Dextran, pullulan, and microcrystalline cellulose were cross-linked with 1-chloro-2,3-epoxypropane and reacted with N-(1-chloroethyl)-N,N-diethylamine or N-glycidyl-N,N,N-trialkylammonium chloride in order to obtain sorbents containing tertiary amino and/or quaternary ammonium groups. In vitro equilibrium sorption of cholic acid on these sorbents was studied in comparison with Cholestyramine, and in vitro dissociation of ionic complexes of cholic acid-sorbents was determined under dynamic conditions. The sorption capacity and the affinity of these sorbents for cholic acid were investigated in relation to the nature of the polymeric support, the swelling porosity of sorbent, the basicity of amino groups, and the nature of the substituents at the nitrogen atom. The maximum sorption capacity increases with the increase in amino group content, their basicity, and the length of alkyl substituents at the nitrogen atom. The affinity for cholic acid of all polysaccharide-based sorbents is higher than that of Cholestyramine. Dextran-based sorbents display the highest sorption affinity. It was found that there exists an optimum swelling porosity for the polysaccharide sorbents to attain the highest affinity for cholic acid. The dissociation rate of ionic complexes depends also on the nature of the polysaccharide and the swelling porosity and its lower for sorbents with higher sorption affinity.

endo-endo-anti Diels-Alder diadduct of hexachlorocyclopentadiene with 1,6-dioxacyclodeca-3,8-diene

There are two independent molecules of endo-endo-anti-1,7,8,9,10,16,17,18,19,19,20,20-dodecachloro-4,13- dioxapentacyclo[14.2.1.1(7,10).0(2,15).0(6,11)]icosa-8,17-di ene, C18H12Cl12O2, in the unit cell with different conformations. In one, the ten-membered ring adopts a chair-chair conformation, and in the other, it adopts a distorted chair-chair conformation. There are near-zero torsion angles at the ring-fusion bonds in both forms [1.5 (6) and 8.1 (5) degrees in the chair-chair molecule, and 2.9 (5) and 2.5 (5) degrees in the distorted chair-chair molecule]. The torsion angles about the bonds comprising the sides of the chair-chair are 158.5 (3), -160.7 (3), -146.8 (4) and 155.7 (3) degrees, and those of the distorted chair-chair are 148.0 (3), -146.8 (3), 175.7 (3) and -52.3 (4) degrees. The norbornene C=C bonds have lengths of 1.314 (6) and 1.305 (6) A in the chair-chair molecule, and 1.309 (6) and 1.318 (6) A in the other. The four dioxolane-system O-C bonds have average lengths of 1.411 (5) and 1.421 (5) A in the two independent molecules.

Applicability of competitive and noncompetitive kinetics to the reductive dechlorination of chlorinated ethenes

Reductive dechlorination of chlorinated ethenes has typically been modeled using standard Michaelis-Menten kinetic equations, implying that each dechlorination step is catalyzed by a unique biological factor. An alternative kinetic model is based on the assumption that all steps are mediated by a single factor. These two options are considered in the context of chlorinated ethene degradation by a previously characterized anaerobic culture. Competitive kinetics afford better chi-squared and visual fits of the data set tested.

In vitro genotoxic evaluation of conventional bleached and biobleached softwood pulp mill effluents

The effluents of pulp and paper mills contain about 300 different chemical compounds; many of them are mutagens and clastogens. Genotoxic studies have shown that chlorination stage liquors are significantly more genotoxic, in the Ames Salmonella assay, than the other process of lignin extraction, and that lyophilized effluents are genotoxic in cultured mammalian cells. Since these effluents from conventional bleaching stages are genotoxic, Chilean industries are interested in changing this process to a less toxic one, such as biobleaching using enzymes. In this study, we tested the in vitro genotoxicity of two types of effluents: an effluent obtained from a conventional radiata pine kraft-bleaching process (effluent D) and one derived from a biobleaching process with hemicellulase (effluent B). Both effluents were tested without any concentration or purification steps in the Ames Salmonella assay (TA100) and in the micronuclei (MN) and sister chromatid exchange (SCE) tests in CHO cells. The results showed that neither effluent induced base pair substitution mutations in the Ames Salmonella assay, and neither increased the micronucleus frequency in CHO cells. But, both increased the SCE frequencies in CHO cells, showing that this assay is more sensitive than the other ones, and that the two effluents contained chemical compounds in amounts enough to induce in vitro genotoxicity measured by the SCE induction.

Synthesis of phosphotyrosine-containing peptides using bis-(2,2,2-trichloro)ethyl groups for phosphate protection

Suitability of bis-(2,2,2-trichloro)ethyl (Tc) groups for protection of phosphate moiety in Boc-mode synthesis of phosphotyrosine peptides is demonstrated Boc-Tyr(PO3Tc2)-OH and Fmoc-Tyr(PO3Tc2)-OH were prepared by acylating H-Tyr(PO3Tc2)-OH with (Boc)2O and Fmoc-ONSu, respectively. Phosphorus introduction was achieved by phosphorylating Boc-Tyr-OBzl with Tc phosphochloride. The Tc-phosphorus protector was found to be incompatible with the Fmoc group because the conditions of Fmoc removal (piperidine treatment) caused dephosphorylation. Complete NMR spectral assignments in the described compounds is presented. (Contribution No. 2398 from the Centre for Food and Animal Research).

Chloropicrin: reactions with biological thiols and metabolism in mice

Chloropicrin (CCl3NO2) is a preplant soil fumigant as a fungicide, warning agent for other fumigants, and former was gas. Its mode of action is unknown but presumably related to its facile metabolic dechlorination on reaction with biological thiols. These interactions were studied with 14CCl3NO2, 14CHCl2NO2, 14CH2ClNO2, and 14CH3NO2, synthesized for this purpose. Reaction of 14CCl3NO2 with GSH yields the di- and monochloro derivatives, GSSG, and a small amount of nitrite. The initial adduct with GSH is transient, but more stable derivatives are formed at longer times or on catalysis by GSH S-transferase. Human Hb, examined as a model thiol protein, reacts with 1.5 mol equiv of 14CCl3NO2 at pH 7.4 to produce 53-67% 14CHCl2NO2 and 10-11% Hb dducts (radiochemical yields) which, on longer incubation, release 14CHCl2NO2, CHCl2NO2 and CH2ClNO2 react with the same site(s) in Hb but more slowly. The dechlorination reactions are also catalyzed by liver cytosol and microsomes with NADPH. Dechlorination and adduct formation observed in vitro also occur in vivo in ip-treated mice. Thus, 14CCl3NO2 quickly gives 14CHCl2NO2, and some 14CO2 is formed, but the primary urinary metabolites are polar and nonvolatile. The major metabolite from 14CCl3NO2 in urine is less polar than those from 14CHCl2NO2, 14CH2ClNO2, and 14CH3NO2 which, in turn, are different from the 14CH2O and H14CO2Na metabolites. Liver tissue is adducted in vivo by 14CCl3NO2 (43% radiocarbon unextractable with methanol at 1 h), but the total radiocarbon content decreases 4-fold between 1 and 48 h after treatment. Liver effects from a high CCl3NO2 dose are associated with 19% less GSH and 50% more absorbance from soluble hemoproteins than controls. The toxicity of CCl3NO2 is probably due to disruption of multiple targets by its cascade of dechlorination products.

Stability of microcystins from cyanobacteria--IV. Effect of chlorination on decomposition

Microcystins, the cyclic heptapeptide toxins produced by cyanobacteria such as Microcystis, show tumor-promoting activity through inhibition of protein phosphatases 1 and 2A. They potentially threaten human health, and are increasing the world-wide interest in the health risk associated with cyanobacterial toxins. In this study, the effect of chlorination on the decomposition of microcystins-LR and -RR was examined. The toxins were easily decomposed by chlorination with sodium hypochlorite, and the decomposition depended on the free chlorine dose. In this operation, many reaction products were formed, one of which was determined to be dihydroxymicrocystin formed through the chloronium ion at the conjugated diene of Adda [3-amino-9-methoxy-10-phenyl-2,6,8-trimethyl-deca-4(E), 6(E)-dienoic acid], followed by hydrolysis. Other products may be its stereoisomers and/or regioismers. No noxious products were detected from the chlorination process of microcystin-LR. Although these results suggested that chlorination at an adequate chlorine dose is very effective for the removal of microcystin in raw water, preoxidation of the cell itself with chlorine must be avoided, because it frequently causes toxin release from algae and produce trihalomethanes during water treatment.

Additivity in microbial toxicity of nonuniform mixtures of organic chemicals

Microbial toxicity of nonuniform mixtures of selected synthetic organic chemicals in several proportion is evaluated. Toxicity is quantified by the inhibition of oxygen uptake rate of a surrogate microbial text culture as measured by a respirometer. The joint toxic effects of the chemicals are analyzed for simple addition using toxic units (TU) and similarity parameters (lambda). A new approach is proposed to assign acceptance limits to sigma(TU)i and lambda to account for experiment errors and variances. Based on this approach, the joint toxic effects of 16 chemicals evaluated in this study in 14 different mixtures were found to be simply additive. Predictions of component concentration based on simple additivity agreed with the measured values within an average factor of error of 1.4.

Anaerobic dehalogenases

Several anaerobic bacteria are able to reductively dehalogenate chlorinated hydrocarbons and to couple this reaction to the synthesis of ATP via a chemiosmotic mechanism (dehalorespiration). A few reductive dehalogenases have recently been purified and characterized. Preliminary investigations have been performed to elucidate the mechanism of dehalorespiration.

Diverse mechanistic approaches to difficult chemical transformations: microbial dehalogenation of chlorinated aromatic compounds

Chlorinated aromatic compounds represent an important class of environmental pollutants. Microbial dehalogenases play a crucial role in the biodegradation of these compounds. The three major classes of aromatic dehalogenases are discussed in this minireview.