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PubMed2000

Monitoring of urban traffic emissions using some physiological indicators in Ricinus communis L. plants.

Plants of Ricinus communis L. in the city of Porto Alegre, in southern Brazil, were exposed to urban traffic exhaust emissions for 5 months and compared with controls kept at a site essentially free of direct motor vehicle emissions. No symptomatic visible injuries were observed, but significant differences could be measured in growth, enzymatic activities of total peroxidase and nitrate reductase, chlorophyll content, leaf buffering capacity, and N contents in leaves. Additionally, these data were compared with results from fumigation experiments under controlled conditions. The study showed that some physiological parameters in R. communis L. plants could be used as an appropriate bioindicator system for urban traffic contamination, and therefore it is recommended that dose-response relationships should be developed.

Air Pollutants↗
PubMed2001

Urinary bromide levels probably dependent to intake of foods such as sea algae.

The purpose of the present study is to examine if the bromide (Br) level in urine (Br-U) varies substantially among adult general populations of either sex or of different dietary habits. For this purpose, morning spot urine samples (about 50 per group) were collected from six groups of people, i.e., one group each of men and women in a city in Japan (thus two groups in Japan) and one group each of women in two urban and two rural areas in central and northeast China (four groups in China). The samples were analyzed for Br by ECD-gas chromatography after derivatization to methyl bromide. Br-U essentially followed a normal distribution. Whereas there was only a marginal difference in Br-U between men (7.7 +/- 2.5 mg/L as an arithmetic mean and arithmetic standard deviation) and women (8.1 +/- 2.9 mg/L) in Japan, and no difference between the urban (2.3 +/- 0.8 mg/L) and rural women (2.6 +/- 1.1 mg/L) in China, the difference between Japanese (8.1 +/- 2.9 mg/L) and Chinese women (2.3 +/- 0.8 mg/L for two cities and 2.6 +/- 1.1 mg/L for two villages) was substantial. A literature survey suggested variation in dietary habits, especially that in sea algae intake, is a possible factor affecting the observed difference in Br-U between the two ethnic groups. Contribution of Br in cereals after fumigation with, e.g., methyl bromide, was also thought to be possible. The implication of difference in background Br-U levels is discussed in relation to biological monitoring of exposure to Br-containing industrial chemicals, such as 1- and 2-bromopropane.

Adult↗
PubMed2004

The relationship between microbial community structure and functional stability, tested experimentally in an upland pasture soil.

Soil collected from an upland pasture was manipulated experimentally in ways shown previously to alter microbial community structure. One set of soil was subjected to chloroform fumigation for 0, 0.5, 2, or 24 h and the other was sterilised by gamma-irradiation and inoculated with a 10(-2), 10(-4), 10(-6), or 10(-8) dilution of a soil suspension prepared from unsterilized soil. Following incubation for 8 months, to allow for the stabilization of microbial biomass and activity, the resulting microbial community structure (determined by PCR-DGGE of bacterial specific amplification products of total soil DNA) was assessed. In addition, the functional stability (defined here as the resistance and resilience of short-term decomposition of plant residues to a transient heat or a persistent copper perturbation) was determined. Changes in the active bacterial population following perturbation (determined by RT-PCR-DGGE of total soil RNA) were also monitored. The manipulations resulted in distinct shifts in microbial community structure as shown by PCR-DGGE profiles, but no significant decreases in the number of bands. These shifts in microbial community structure were associated with a reduction in functional stability. The clear correlation between altered microbial community structure and functional stability observed in this upland pasture soil was not evident when the same protocols were applied to soils in other studies. RT-PCR-DGGE profiles only detected a shift in the active bacterial population following heat, but not copper, perturbation. We conclude that the functional stability of decomposition is related to specific components of the microbial community.

Analysis of Variance↗
PubMed2004

Characterization of humus microbial communities in adjacent forest types that differ in nitrogen availability.

To address the link between soil microbial community composition and soil processes, we investigated the microbial communities in forest floors of two forest types that differ substantially in nitrogen availability. Cedar-hemlock (CH) and hemlock-amabilis fir (HA) forests are both common on northern Vancouver Island, B.C., occurring adjacently across the landscape. CH forest floors have low nitrogen availability and HA high nitrogen availability. Total microbial biomass was assessed using chloroform fumigation-extraction and community composition was assessed using several cultivation-independent approaches: denaturing gradient gel electrophoresis (DGGE) of the bacterial communities, ribosomal intergenic spacer analysis (RISA) of the bacterial and fungal communities, and phospholipid fatty acid (PLFA) profiles of the whole microbial community. We did not detect differences in the bacterial communities of each forest type using DGGE and RISA, but differences in the fungal communities were detected using RISA. PLFA analysis detected subtle differences in overall composition of the microbial community between the forest types, as well as in particular groups of organisms. Fungal PLFAs were more abundant in the nitrogen-poor CH forests. Bacteria were proportionally more abundant in HA forests than CH in the lower humus layer, and Gram-positive bacteria were proportionally more abundant in HA forests irrespective of layer. Bacterial and fungal communities were distinct in the F, upper humus, and lower humus layers of the forest floor and total biomass decreased in deeper layers. These results indicate that there are distinct patterns in forest floor microbial community composition at the landscape scale, which may be important for understanding nutrient availability to forest vegetation.

Bacteria↗
PubMed2005

Heterotrophic fixation of CO(2) in soil.

The occurrence of heterotrophic CO(2) fixation by soil microorganisms was tested in several mineral soils differing in pH and two artificial soils (a mixture of silica sand, alfalfa powder, and nutrient medium inoculated with a soil suspension). Soils were incubated at ambient ( approximately 0.05 vol%) and elevated ( approximately 5 vol%) CO(2) concentrations under aerobic conditions for up to 21 days. CO(2) fixation was detected using either a technique for determining the natural abundance of (13)C or by measuring the distribution of labeled (14)C-CO(2) in soil and bacteria. The effects of elevated CO(2) on microbial biomass (direct counts, chloroform fumigation extraction method), composition of microbial community (phospholipid fatty acids), microbial activity (respiration, dehydrogenase activity), and turnover rate were also measured. Heterotrophic CO(2) fixation was proven in all soils under study, being higher in neutral soils. The main portion of the fixed CO(2) (98-99%) was found in extracellular metabolites while only approximately 1% CO(2) was incorporated into microbial cells. High CO(2) concentration always induced an increase in microbial activity, changes in the composition of the microbial community, and a decrease in microbial turnover. The results suggest that heterotrophic CO(2) fixation could be a widespread process in soils.

Bacteria↗
PubMed2005

Microbial community structure and density under different tree species in an acid forest soil (Morvan, France).

Overexploitation of forests to increase wood production has led to the replacement of native forest by large areas of monospecific tree plantations. In the present study, the effects of different monospecific tree cover plantations on density and composition of the indigenous soil microbial community are described. The experimental site of "Breuil-Chenue" in the Morvan (France) was the site of a comparison of a similar mineral soil under Norway spruce (Picea abies), Douglas fir (Pseudotuga menziesii), oak (Quercus sessiflora), and native forest [mixed stand dominated by oak and beech (Fagus sylvatica)]. Sampling was performed during winter (February) at three depths (0-5, 5-10, and 10-15 cm). Abundance of microorganisms was estimated via microbial biomass measurements, using the fumigation-extraction method. The genetic structure of microbial communities was investigated using the bacterial- and fungal-automated ribosomal intergenic spacer analysis (B-ARISA and F-ARISA, respectively) DNA fingerprint. Only small differences in microbial biomass were observed between tree species, the highest values being recorded under oak forest and the lowest under Douglas fir. B- and F-ARISA community profiles of the different tree covers clustered separately, but noticeable similarities were observed for soils under Douglas fir and oak. A significant stratification was revealed under each tree species by a decrease in microbial biomass with increasing depths and by distinct microbial communities for each soil layer. Differences in density and community composition according to tree species and depth were related to soil physicochemical characteristics and organic matter composition.

Bacteria↗
PubMed2003

Ploidy variation among herbicide-resistant bermudagrass plants of cv. TifEagle transformed with the bar gene.

A protocol was developed for biolistic transformation of hybrid bermudagrass cv. TifEagle using the bar gene. TifEagle is an ultradwarf used exclusively on golf greens. Herbicide resistance should serve as a useful management tool, especially if methyl-bromide is unavailable for fumigation prior to plant establishment. Hybrid bermudagrass is completely sterile, which should limit the chance of gene escape via out-crossing. Sliced nodes were used to initiate embryogenic tissue cultures on MS medium supplemented with 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.01 mg/l 6-benzylaminopurine (BA). Embryogenic tissue was bombarded with the bar gene, and herbicide-resistant tissue was selected in the dark on medium supplemented with 0.75 mg/l 2,4-D, 0.01 mg/l BA and 5-15 mg/l phosphinothricin (PPT). Resistant somatic embryos were induced to germinate in the light on MS medium supplemented with 0.13 mg/l 2,4-D and 0.5 mg/l BA. Plants were transferred to the greenhouse after rooting in the presence of 10-15 mg/l PPT and testing positive in a chlorophenol red assay. A total of 89 herbicide-resistant plants were recovered from at least nine independent events from six separate bombardments, although the number of independent transformation events was not confirmed for the entire group. Flow cytometry indicated that most of the plants (82/89) were hexaploid and that the remaining seven plants were triploid. The hexaploid plants were a darker green than the triploids or TifEagle control. Other variation, present only in the hexaploids, included an increased leaf width and length. Southern blot hybridization confirmed genomic integration of the bar gene in triploid and a subset of hexaploid herbicide-resistant plants. AFLP analysis did not indicate changes in DNA profiles using [33P] and a sample of 32 hexaploid plants recovered from a single bombardment. DNA profiles were very similar to that of the TifEagle control with a semi-automated fluorescence-based AFLP.

Culture Techniques↗
PubMed2003

Induction of early light-inducible protein gene expression in Pisum sativum after exposure to low levels of UV-B irradiation and other environmental stresses.

Plants are constantly subjected to environmental changes and have developed various defence mechanisms to facilitate their continued existence. Pisum sativum plants were exposed to low levels of UV-B radiation and ELIP (early light-inducible proteins) mRNA, with a probable protective function, was rapidly and strongly induced during this type of stress. To our knowledge, this is the only photosynthetic gene that is up-regulated following exposure to UV-B, and this result has to be compared with studies predominantly reporting down-regulation by UV-B of genes encoding proteins localised in the plastid. The expression pattern of ELIP mRNA in pea was also investigated during salt, wounding and ozone stress. The transcript levels of ELIP were induced after the salt and wounding treatments but not during ozone fumigation.

Arabidopsis Proteins↗
PubMed2003

Arabidopsis sulfurtransferases: investigation of their function during senescence and in cyanide detoxification.

Sulfurtransferases (STs) and beta-cyano- l-alanine synthase (CAS) are suggested to be involved in cyanide detoxification. Therefore, the accumulation of ST1 and CAS RNAs, and the ST and CAS protein levels and enzyme activities were determined in Arabidopsis thaliana Heynh. plants grown under different conditions. Senescence-associated processes were successfully induced by natural aging, by jasmonate methyl ester and by darkness in whole plants and detached leaves, as demonstrated by the expression of the senescence marker genes SAG12 and SAG13. However, the changes in RNA accumulation and protein levels of ST and CAS did not correlate with the expression of these senescence marker genes; the specific ST and CAS activities either decreased (ST) or increased (CAS). In another experiment, Arabidopsis plants were sprayed with cyanide to investigate the role of ST and CAS in cyanide detoxification. The expression of ST and CAS at the RNA and protein levels, and also the enzyme activities, remained equal in cyanide-treated and control plants. Incubation with 1-aminocyclopropane-1-carboxylic acid, the precursor of ethylene, increased while fumigation with ethylene decreased expression and activity of ST and CAS. In summary, cyanide does not induce the expression or enhance the activity of ST and CAS in Arabidopsis. For both proteins the evidence for a role in cyanide detoxification or induced senescence is low.

Acetates↗
PubMed2000

pH regulation in apoplastic and cytoplasmic cell compartments of leaves.

The regulation of pH in the apoplast, cytosol and chloroplasts of intact leaves was studied by means of fluorescent pH indicators and as a response of photosynthesis to acid stress. The apoplastic pH increased under anaerobiosis. Aeration reversed this effect. Apoplastic responses to CO2, HCl or NH3 differed considerably. Whereas HCl and ammonia caused rapid acidification or alkalinization, the return to initial pH values was slow after cessation of fumigation. Addition of CO2 either did not produce the acidification expected on the basis of known apoplastic buffering or even caused some alkalinization. Removal of CO2 shifted the apoplastic pH into the alkaline range before the pH returned to initial steady-state levels. In the presence of vanadate, the alkaline shift was absent and the apoplastic pH returned slowly to the initial level when CO2 was removed from the atmosphere. In contrast to the response of the apoplast, anaerobiosis acidified the cytosol or, in some species, had little effect on its pH. Acidification was rapidly reversed upon re-admission of oxygen. The CO2-dependent pH changes were very fast in the cytosol. Considerable alkalinization was observed after removal of CO2 under aerobic, but not under anaerobic conditions. Rates of the re-entry of protons into the cytosol during recovery from CO2 stress increased in the presence of oxygen with the length of previous exposure to high CO2. Effective pH regulation in the chloroplasts was indicated by the recovery of photosynthesis after the transient inhibition of photosynthetic electron flow when CO2 was increased from 0.038% to 16% in air. As photosynthesis became inhibited under high CO2, reduction of the electron transport chain increased transiently. The time required for recovery of photosynthesis from inhibition during persistent CO2 stress was similar to the time required for establishing steady-state pH values in the cytosol under acid stress. The high capacity of leaf cells for the rapid re-attainment of pH homeostasis in the apoplast and the cytoplasm under acid or alkaline stress suggested the rapid activation or deactivation of membrane-localised proton-transporting enzymes and corresponding ion channel regulation for co-transport of anions or counter-transport of cations together with proton fluxes. Acidification of the cytoplasm appeared to activate energy-dependent proton export primarily into the vacuoles whereas apoplastic alkalinization resulted in the pumping of protons into the apoplast. Proton export rates from the cytosol into the apoplast after anaerobiosis were about 100 nmol (m2 leaf area)(-1) s(-1) or less. Proton export under acid stress into the vacuole was about 1200 nmol m(-2) s(-1). The kinetics of pH responses to the addition or withdrawal of CO2 indicated the presence of carbonic anhydrase in the cytosol, but not in the apoplast.

Aerobiosis↗
PubMed2005

Soil microbial diversity and soil functioning affect competition among grasses in experimental microcosms.

A gradient of microbial diversity in soil was established by inoculating pasteurized soil with microbial populations of different complexity, which were obtained by a combination of soil fumigation and filtering techniques. Four different soil diversity treatments were planted with six different grass species either in monoculture or in polyculture to test how changes of general microbial functions, such as catabolic diversity and nutrient recycling efficiency would affect the performance of the plant communities. Relatively harsh soil treatments were necessary to elicit visible effects on major soil processes such as decomposition and nitrogen cycling due to the high redundancy and resilience of soil microbial communities. The strongest effects of soil diversity manipulations on plant growth occurred in polycultures where interspecific competition between plants was high. In polycultures, soil diversity reduction led to a gradual, linear decline in biomass production of one subordinate grass species (Bromus hordeaceus), which was compensated by increased growth of two intermediate competitors (Aegilops geniculata, B. madritensis). This negative covariance in growth of competing grass species smoothed the effects of soil diversity manipulations at the plant community level. As a result, total shoot biomass production remained constant. Apparently the effects of soil diversity manipulations were buffered because functional redundancy at both, the microbial and the plant community level complemented each other. The results further suggests that small trade-offs in plant fitness due to general functional shifts at the microbial level can be significant for the outcome of competition in plant communities and thus diversity at much larger scales.

Biodiversity↗
PubMed2006

Soil respiration in northern forests exposed to elevated atmospheric carbon dioxide and ozone.

The aspen free-air CO2 and O3 enrichment (FACTS II-FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO2) and elevated tropospheric ozone (O3) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O3 treatment. Elevated CO2 significantly stimulated soil respiration (8-26%) compared to the control treatment in both community types over all three growing seasons. In years 6-7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO2 + O3), and rates of soil respiration were 15-25% greater in this treatment than in the elevated CO2 treatment, depending on year and community type. Two of the treatments, elevated CO2 and elevated CO2 + O3, were fumigated with 13C-depleted CO2, and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60-80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4-6 per thousand enriched in 13C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4-6 per thousand more depleted in 13C. Up to 50% of the Earth's forests will see elevated concentrations of both CO2 and O3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study.

Acer↗
PubMed2002

Molecular and biochemical analysis of serine acetyltransferase and cysteine synthase towards sulfur metabolic engineering in plants.

Serine acetyltransferase (SATase) and cysteine synthase (O-acetylserine (thiol)-lyase) (CSase) are committed in the final step of cysteine biosynthesis. Six cDNA clones encoding SATase have been isolated from several plants, e.g. watermelon, spinach, Chinese chive and Arabidopsis thaliana. Feedback-inhibition pattern and subcellular localization of plant SATases were evaluated. Two types of SATase that differ in their sensitivity to the feedback inhibition by L-cysteine were found in plants. In Arabidopsis, cytosolic SATase was inhibited by L-cysteine at a physiological concentration in an allosteric manner, but the plastidic and mitochondrial forms were not subjected to this feedback regulation. These results suggest that the regulation of cysteine biosynthesis through feedback inhibition may differ depending on the subcellular compartment. The allosteric domain responsible for L-cysteine inhibition was characterized, using several SATase mutants. The single change of amino acid residue, glycine-277 to cysteine, in the C-terminal region of watermelon SATase caused a significant decrease of the feedback-inhibition sensitivity of watermelon SATase. We made the transgenic Arabidopsis overexpressing point-mutated watermelon SATase gene whose product was not inhibited by L-cysteine. The contents of OAS, cysteine, and glutathione in transgenic Arabidopsis were significantly increased as compared to the wild-type Arabidopsis. Transgenic tobacco (Nicotiana tabacum) (F1) plants with enhanced CSase activities both in the cytosol and in the chloroplasts were generated by cross-fertilization of two transgenic tobacco expressing either cytosolic CSase or chloroplastic CSase. Upon fumigation with 0.1 microLL(-1) sulfur dioxide, both the cysteine and glutathione contents in leaves of F1 plants were increased significantly, but not in leaves of non-transformed control plants. These results indicated that both SATase and CSase play important roles in cysteine biosynthesis and its regulation in plants.

Acetyltransferases↗
PubMed1999

The tooth-worm: historical aspects of a popular medical belief.

The concept of a tooth-worm, which according to popular belief, caused caries and periodontitis, has existed in diverse cultures and across the ages. During the Enlightenment, however, the theory of the tooth-worm was assigned by medical doctors almost exclusively to superstition. Even so, the idea that toothache was caused by gnawing worms held on even into this century. There were many different ideas with regard to the appearance of tooth-worms. In England, for instance, it was thought that the tooth-worm looked like an eel. In Northern Germany, people supposed the tooth-worm to be red, blue, and gray and in many cases the worm was compared to a maggot. The gnawing worm was held responsible for many evils and, in particular, was blamed for toothache provoked by caries. The question is discussed of how the belief in the existence of the tooth-worm in former times can be explained. In popular medicine, numerous therapies were applied in order to eradicate the tooth-worm. In addition to the fumigations with henbane seeds, which allowed the "tooth-worm" to develop in the form of burst seeds, there were also magical formulas and oaths.

Arab World↗
PubMed2006

Vapor activity of 72 essential oils against a Trichophyton mentagrophytes.

For practical application for vapor therapy and fumigation, the vapor activity of 72 essential oils was screened against a Trichophyton mentagrophytes, using a closed box. The fungicidal activity, expressed as the minimum fungicidal dose (MFD), was determined from the colony size, which was correlated with the inoculum size. Oils containing phenol as the major component showed the most potent vapor activity, with an MFD of 1.56 microg/ml air. This was followed by oils with aldehyde as the major component, then by those with alcohol as the major component. The vapor activities of oils containing ketone, ester, and ether/oxide components were decreased, in that order. The oils that were rich in hydrocarbon components had the weakest activity. The same tendency was observed with the components themselves. Phenols and aldehydes exhibited the highest vapor activity, followed by alcohols, ketone, ester, ether/oxide, and hydrocarbon. There was a rough correlation between the vapor activity determined by the box vapor assay and the contact activity determined by agar diffusion assay. But oils containing sesquiterpenes showed weaker vapor activity than that expected from the contact activity. Based on the activity-chemical structure relationship, the 72 oils were classified into seven functional groups.

Antifungal Agents↗
PubMed2005

Effect of volatile constituents from Securidaca longepedunculata on insect pests of stored grain.

Securidaca longepedunculata Fers (Polygalaceae) is commonly used as a traditional medicine in many parts of Africa as well as against a number of invertebrate pests, including insects infesting stored grain. The present study showed that S. longepedunculata root powder, its methanol extract, and the main volatile component, methyl salicylate, exhibit repellent and toxic properties to Sitophilus zeamais adults. Adult S. zeamais that were given a choice between untreated maize and maize treated with root powder, extract, or synthetic methyl salicylate in a four-way choice olfactometer significantly preferred the control maize. Methyl salicylate vapor also had a dose-dependant fumigant effect against S. zeamais, Rhyzopertha dominica, and Prostephanus truncates, with a LD100 achieved with a 60microl dose in a 1-l container against all three insect species after 24 hr of exposure. Probit analyses estimated LD50 values between 34 and 36 microl (95% CI) for all insect species. Furthermore, prolonged exposure for 6 days showed that lower amounts (30 microl) of methyl salicylate vapor were able to induce 100% adult mortality of the three insect species. The implications are discussed in the context of improving stored product pest control by small-scale subsistence farmers in Africa.

Animals↗
PubMed1990

Extramitochondrial release of hydrogen peroxide from insect and mouse liver mitochondria using the respiratory inhibitors phosphine, myxothiazol, and antimycin and spectral analysis of inhibited cytochromes.

The fumigant insecticide phosphine (PH3) is known to inhibit cytochrome c oxidase in vitro. Inhibition of the respiratory chain at this site has been shown to stimulate the generation of superoxide radicals (O2-), which dismutate to form hydrogen peroxide (H2O2). This study was performed in order to investigate the production of H2O2 by mitochondria isolated from granary weevil (Sitophilus granarius) and mouse liver on exposure to PH3. Other respiratory inhibitors, antimycin, myxothiazol, and rotenone were used with insect mitochondria. Hydrogen peroxide was measured spectrophotometrically using yeast cytochrome c peroxidase as an indicator. Insect and mouse liver mitochondria, utilizing endogenous substrate, both produced H2O2 after inhibition by PH3. Insect organelles released threefold more H2O2 than did mouse organelles, when exposed to PH3. Production of H2O2 by PH3-treated insect mitochondria was increased significantly on addition of the substrate alpha-glycerophosphate. Succinate did not enhance H2O2 production, however, indicating that the H2O2 did not result from the autoxidation of ubiquinone. NAD(+)-linked substrates, malate and pyruvate also had no effect on H2O2 production, suggesting that NADH-dehydrogenase was not the source of H2O2. Data obtained using antimycin and myxothiazol, both of which stimulated the release of H2O2 from insect mitochondria, lead to the conclusion that glycerophosphate dehydrogenase is a source of H2O2. The effect of combining PH3, antimycin, and myxothiazol on cytochrome spectra in insect mitochondria was also recorded. It was observed that PH3 reduces cytochrome c oxidase but none of the other cytochromes in the electron transport chain. There was no movement of electrons to cytochrome b when insect mitochondria are inhibited with PH3. The spectral data show that the inhibitors interact with the respiratory chain in a way that would allow the production of H2O2 from the sites proposed previously.

Animals↗
PubMed1996

Inter-individual variability in the oxidation of 1,2-dibromoethane: use of heterologously expressed human cytochrome P450 and human liver microsomes.

1,2-Dibromoethane (1,2-DBE) is mainly used as an additive in leaded gasoline and as a soil fumigant and it is a suspected carcinogen in humans. In this study, the oxidative bioactivation of 1,2-DBE to 2-bromoacetaldehyde (2-BA) was studied using heterologously expressed human cytochrome P450 (P450) isoenzymes and human liver microsomes. Out of ten heterologously expressed human P450 isoenzymes (CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2E1, CYP2C8, CYP2C9, CYP2C18, CYP3A4 and CYP3A5), only human CYP2A6, CYP2B6 and CYP2E1 metabolized 1,2-DBE, albeit with strongly differing catalytic efficiencies. The apparent Km and Vmax values were 3.3 mM and 0.17 pmol/min per pmol P450 for CYP2A6, 9.7 mM and 3.18 pmol/min per pmol P450 for CYP2B6 and 42 microM and 1.3 pmol/min per pmol P450 for CYP2E1, respectively. In all of 21 human liver samples studied, 1,2-DBE was oxidized with activities ranging from 22.2 to 1027.6 pmol/min per mg protein, thus showing a 46-fold inter-individual variability. The kinetics of the oxidative metabolism of 1,2-DBE to 2-BA in human liver microsomes were linear, indicating the involvement of primarily one single P450 isoenzyme. There was a tendency towards a positive correlation between the oxidative metabolism of 1,2-DBE in the human liver microsomes and the 6-hydroxylation of chlorzoxazone, a selective substrate for CYP2E1. Furthermore, the oxidative metabolism of 1,2-DBE was inhibited by the specific CYP2E1 inhibitors disulfiram (DS) and diethyldithiocarbamate (DDC). In contrast, a poor correlation was found between the immunochemically quantified amount of CYP2E1 and the microsomal chlorzoxazone 6-hydroxylation or the 1,2-DBE oxidation. The results indicate that CYP2E1 is probably the major P450 isoenzyme involved in the oxidative hepatic metabolism of 1,2-DBE in humans. The inter-individual variability in the oxidative bioactivation of 1,2-DBE in humans, largely due to inter-individual variability in the catalytic activity of hepatic CYP2E1, may have important consequences for the risk assessment for human exposure to 1,2-DBE.

Acetaldehyde↗