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PubMed2006

Crystal structures of chloroperoxidase with its bound substrates and complexed with formate, acetate, and nitrate.

Chloroperoxidase (CPO) is a heme-thiolate enzyme that catalyzes hydrogen peroxide-dependent halogenation reactions. Structural data on substrate binding have not been available so far. CPO was therefore crystallized in the presence of iodide or bromide. One halide binding site was identified at the surface near a narrow channel that connects the surface with the heme. Two other halide binding sites were identified within and at the other end of this channel. Together, these sites suggest a pathway for access of halide anions to the active site. The structure of CPO complexed with its natural substrate cyclopentanedione was determined at a resolution of 1.8 A. This is the first example of a CPO structure with a bound organic substrate. In addition, structures of CPO bound with nitrate, acetate, and formate and of a ternary complex with dimethylsulfoxide (Me2SO) and cyanide were determined. These structures have implications for the mechanism of compound I formation. Before binding to the heme, the incoming hydrogen peroxide first interacts with Glu-183. The deprotonated Glu-183 abstracts a proton from hydrogen peroxide. The hydroperoxo-anion then binds at the heme, yielding compound 0. Glu-183 protonates the distal oxygen of compound 0, water is released, and compound I is formed.

Acetic Acid↗
PubMed1983

Bioassay of extracts of ambient particulate matter.

Organic extracts from airborne particles collected at various sites in Scandinavia have been tested for mutagenicity in the Ames Salmonella/microsome assay. Extracts from particles in the respirable size fraction (diameter less than 3 microns) were mutagenic with and without metabolic activation. The mutagenic activity varied from day to day, mainly due to variations in meteorological parameters, especially wind speed and atmospheric stability. A seasonal variation could also be observed, with the highest average values in winter time. Samples collected in urban areas were considerably more mutagenic than samples from background areas. The results suggest that exhaust from motor vehicles are the most important source of mutagenic particles in urban areas. Comparison of roof top samples with street level samples indicated that atmospheric reactions cause transformation of nonpolar compounds in the primary emission to more oxygenated mutagenic compounds. It is, however, not known to which degree this causes an overall increase of the mutagenic activity. The mutagenic activity of emissions from stationary combustion sources have also been studied, and residential heating by burning solid fuels in small combustion units have been shown to be a major contributor to mutagens in the environment.

Air Pollutants↗
PubMed1990

Inhibition of human polymorphonuclear leukocyte respiratory burst activity and aggregation by 6-ketocholestanol.

6-ketocholestanol, a naturally occurring oxygenated sterol, when incubated with human neutrophils (PMN), can inhibit superoxide and hydrogen peroxide generation in a dose-dependent fashion. This is accompanied by inhibition of stimulated PMN aggregation without alteration in cellular viability. This inhibitory effect is not affected by washing of the cells, and cannot be blocked by the addition of free cholesterol to the medium. These data are consistent with prior observations which showed an inhibitory effect on PMN chemotaxis by certain oxygenated sterol compounds, and support the hypothesis that certain oxygenated sterols can affect a variety of human PMN functions by a mechanism that may involve perturbation of the plasma membrane.

Cell Aggregation↗
PubMed1995

Effects of carnosine and related compounds on generation of free oxygen species: a comparative study.

The effect of carnosine and related compounds on the luminol- and lucigenin-dependent luminescence of rabbit leukocytes, activated by BaSO4, has been studied. Carnosine was found to modify BaSO4-induced chemiluminescence of leukocytes via suppression of hypochlorous anion generation with simultaneous stimulation the system of oxygen superoxide anion. Additionally to this effect carnosine prevents enzymic dismutation of O2.. Anserine, acetylanserine, and homocarnosine also possess the ability to activate O.2 production by leukocytes. The effect is not inherent to imidazole used in the same concentrations. Suppression of myeloperoxidase reaction by carnosine and related compounds is explained by both inhibiting action on the enzyme itself, and direct neutralization of hypochlorous anion due to formation of stable chloroamine complexes. Methylation of carnosine at N1 nitrogen of imidazole ring, leading to anserine, forced inhibition of myeloperoxidase system, whereas its acetylation at the free beta-amino group weakened this effect.

Acetylation↗
PubMed2005

[Effect of oxygen and nitrogen active compounds on pH value in myometrium myocytes].

In suspension from a rat uterus using fluorescent pH1 probe BCECF-AM was established that the "apparent" pH1 value for this object was 6.72 +/- 0.02 at pHo = 7,4 (t = 25 degrees C, n = 5). Cell activation by 0.1 mM carbachol was accompanied by a rise in cytosolic pH up to 6.81 +/- 0.01. This process with different efficiency was inhibited by blockers of K(+)- and H(+)-channels: 0.1 mM 4-amidopyridine, tetraethilamonium and cadmium. The blockers of passive H(+)-transport do not inhibit completely alkalization of myoplasm that can testify in the favor of the non-channel way of passive transport H+ through plasmalemma. It was established that NO (0.1 mM sodium nitroprusside) and NO2- (10 nM) significantly enhanced the carbochol-induced rise of myoplasm pH in the cells from myometrium. It also was shown that carbachol-induced pH. in myocytes was increased by the addition of 10 nM H2O2. It was suggested that the studied compounds could influence Ca2+ transport systems by changing pH in myocytes.

Animals↗
PubMed1991

Mechanism for the generation of superoxide anion and singlet oxygen during heme compound-catalyzed linoleic acid hydroperoxide decomposition.

Heme compound, hematin or cytochrome c, catalyzes the decomposition of 13-hydroperoxy linoleic acid yielding both O2- and 1O2 under aerobic conditions. No 1O2 is produced when hydrogen peroxide and cumene hydroperoxide are used as substrates. In these experiments, both O2- and 1O2 could be precisely detected by a chemiluminescence method using a cypridina luciferin analog, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin++ +-3-one, as a chemiluminescence probe, in the absence and presence of Cu-Zn superoxide dismutase in catalytic amounts. The reduction and oxidation cycle of ferric heme compound and the bimolecular reaction of peroxyl radicals are plausible reaction mechanisms for O2- and 1O2 production, respectively, in the systems studied.

Catalysis↗
PubMed2002

Monitoring of the gasoline oxygenate MTBE and BTEX compounds in groundwater in Catalonia (northeast Spain).

Headspace (HS) gas chromatography with flame ionisation detection (HS-GC-FID) and purge and trap (P) gas chromatography-mass spectrometry (P) were used for the determination of methyl-tert-butyl ether (MTBE) and benzene, toluene, and xylenes (BTEX) in groundwater. In this work, we present the first data on the levels of MTBE and BTEX in different groundwater wells in the area of Catalonia (northeast Spain). This monitoring campaign corresponded to 28 groundwater wells that were located near petrol service stations, oil refinery storage tanks, and/or chemical industry at different locations of Catalonia during the period of 1998/1999. The levels of MTBE detected varied between 4-300 microg/l, but two sites had MTBE levels up to 3 and 13 mg/l. In many cases, the BTEX levels were below 1 microg/l, whereas 7 sites had levels varying from 19 microg/l up to 3 mg/l. Most of them were related to leakage from underground tanks in petrol service stations, while the remaining three corresponded respectively to chemical industrial pollution of undetermined origin and to a leak from high-ground petrol tanks in petrochemical refinery factories. The aquifers involved were constituted by detritus coarse materials, sands, and conglomerates. Piezometric levels were roughly comprised between 3 and 40 m, and permeability (K) and transmissivity (T) values were estimated from field measurements. The MTBE/BTEX ratio was also calculated and reached values up to 250. These values were expected, since if we consider that spilled oxygenated gasoline is the source of well contamination and based on solubility considerations alone, the MTBE source concentrations would be about 200 times higher than any BTEX compounds.

Benzene↗
PubMed1997

Kinetic studies of biodegradation of insoluble compounds by continuous determination of oxygen consumption.

Continuous determination of oxygen consumption by electrolytic respirometry has been experimented as a means to study the biodegradation kinetics of scarcely soluble environmental pollutants. The substrates used were the polycyclic aromatic hydrocarbons (PAH), naphthalene, phenanthrene, anthracene, fluoranthene and pyrene. The definition of an appropriate mode of PAH supply, either as crystals or more generally as a solution in a water non-miscible solvent, was found essential for yielding reproducible biodegradation kinetics. In these conditions, for all compounds tested, oxygen determination was found suitable for quantitative evaluation of PAH biodegradation and formation of biomass and soluble metabolites. The study of biodegradation kinetics with this methodology showed that a first phase of exponential growth could be characterized in most cases, followed by a phase of limited growth. Possible mechanisms involved in insoluble substrate uptake are discussed. During exponential growth, the bacteria utilized (although not necessarily exclusively) the PAH solubilized in the aqueous medium.

Biodegradation, Environmental↗
PubMed2006

Scavenging activity of indole compounds against cisplatin-induced reactive oxygen species.

The antioxidant effects of indole compounds such as melatonin (MLT), tryptophan, and serotonin, on cisplatin (cis-diaminedichloroplatinum, or CDDP)-induced reactive oxygen species (ROS) generation were examined by electron spin resonance (ESR). In addition, DNA fragmentation by CDDP-induced ROS and the effect of MLT on it were analyzed in primary cultures of rat renal tubular epithelial cells. MLT and serotonin had scavenging effects on CDDP-induced hydroxy radicals (*OH), and the scavenging activity of MLT was higher than that of serotonin. The exposure of primary-cultured renal tubular cells to CDDP caused severe cytotoxicity. Tryptophan, serotonin, and 6-OH-MLT did not reduce the CDDP-induced cytotoxicity, whereas MLT did. CDDP exposure induced DNA fragmentation in primary-cultured renal tubular cells, but the simultaneous administration of MLT inhibited the DNA fragmentation. These results indicate that MLT inhibits CDDP-induced cytotoxicity by directly scavenging *OH, and that MLT markedly reduces renal cytotoxicity and DNA fragmentation caused by CDDP-induced ROS in vitro.

Animals↗
PubMed2005

Reporting small Delta 17O values: existing definitions and concepts.

The three-isotope tracer Delta(17)O is increasingly used in atmospheric chemistry and other research areas. Thanks to the development of isotope-ratio mass spectrometry (IRMS), delta(17)O and delta(18)O can be determined with a precision of a few 0.01 per thousand, and values for Delta(17)O may be calculated with similar precision. However, interpreting small and precisely determined Delta(17)O values as a deviation from an expected mass-dependent fractionation process is not straightforward. Several aspects are of high importance. In the present paper we review existing definitions, formulas and some other aspects of Delta(17)O reporting. One of the most confusing aspects is a variance of definitions and corresponding formulas. While Delta(17)O is traditionally defined to characterise a data point, i.e. Delta(17)O is considered as a deviation from an expected mass-fractionation line, the recently introduced definition (Miller MF. Geochim. Cosmochim. Acta 2002; 66: 188) characterises a fractionation line itself, in terms of its ordinate intercept. The formulas corresponding to this definition gives a characteristic for a specific process. When the 'traditionally defined' Delta(17)O is in use, an expected fractionation processes--the key point for Delta(17)O reporting--should be defined and parameterised with the same accuracy as intended for reporting Delta(17)O. When Delta(17)O is reported for a data point, not only a value for lambda but an ordinate intercept of a reference fractionation line should be given with high accuracy. We note that defining a single fractionation process is hardly possible for many natural compounds. For such compounds we propose to use a phenomenological reference line, namely an isotope composition range of natural sources. Next, aspects of Delta(17)O comparison and mass-balance calculations are considered. All the aspects considered for Delta(17)O may be relevant for others three-isotope tracers, e.g. Delta(33)S.

Algorithms↗
PubMed1999

Compounds capable of generating singlet oxygen represent a source of artifactual data in scintillation proximity assays measuring phosphopeptide binding to SH2 domains.

We developed scintillation proximity assays (SPA) to discover compounds which inhibit phosphopeptide binding to Src homology 2 (SH2) domain proteins Grb2 and Syk. An assay artifact is reported here as a caveat to others. The SPA used an antibody to couple glutathione-S-transferase SH2 domain fusion proteins to scintillant beads coated with protein A. A pyrazoloquinolone and indolocarbazole inhibited [3H]phosphopeptide binding in both assays. Their potency in the SPA increased with prolonged (2 to 24 h) assay exposure to ambient light. They were inactive in absence of light and in an alternate binding assay. Both compounds absorbed visible light and generated singlet oxygen based on 2-methylfuran-trapping experiments. Their inhibitory activity was suppressed by the singlet oxygen scavengers sodium azide and dithiothreitol. The results suggest that compounds, not previously considered photosensitizers, generated enough singlet oxygen to damage oxidant-sensitive SPA components. Therefore, this SPA should be protected from light to minimize occurrence of false positives.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Miniature radio-frequency mobility analyzer as a gas chromatographic detector for oxygen-containing volatile organic compounds, pheromones and other insect attractants.

A high electric field, radio-frequency ion mobility spectrometry (RF-IMS) analyzer was used as a small detector in gas chromatographic separations of mixtures of volatile organic compounds including alcohols, aldehydes, esters, ethers, pheromones, and other chemical attractants for insects. The detector was equipped with a 2 mCi 63Ni ion source and the drift region for ion characterization was 5 mm wide, 15 mm long and 0.5 mm high. The rate of scanning for the compensation voltages was 60 V s(-1) and permitted four to six scans to be obtained across a capillary chromatographic elution profile for each component. The RF-IMS scans were characteristic of a compound and provided a second dimension of chemical identity to chromatographic retention adding specificity in instances of co-elution. Limits of detection were 1.6-55 x 10(-11) g with an average detection limit for all chemicals of 9.4 x 10(-11) g. Response to mass was linear from 2-50 x 10(-10) g with an average sensitivity of 4 pA ng(-1). Separations of pheromones and chemical attractants for insects illustrated the distinct patterns obtained from gas chromatography with RF-IMS scans in real time and suggest an analytical utility of the RF-IMS as a small, advanced detector for on-site gas chromatographs.

Chromatography, Gas↗
PubMed1980

Dibutylchloromethyltin chloride, a potent inhibitor of electron transport in plant mitochondria.

Dibutylchloromethyl tin chloride (DBCT) inhibits coupled and uncoupled respiration of mitochondria from potato tubers, cauliflower florets and etiolated mung bean hypocotyls with succinate and L-malate but not with external NADH or TMPD/ascorbate as substrates. Using potato and cauliflower mitochondria. DBCT at 200 pmole/mg of protein gives complete inhibition only in KCl-based media and at pH 6.8. DBCT has no effect on the internal pH of mung bean mitochondria, but does cause a decrease in the membrane potential. Electron transport through the alternative oxidase is not inhibited, neither is the ATP-synthase system. DBCT appears to interact with the functionally-distinct pool of ubiquinone associated with the oxidation of succinate and L-malate.

Electron Transport↗
PubMed2002

Quantitative aspects of inorganic nutrient fluxes in the Gazi Bay (Kenya): implications for coastal ecosystems.

Fluxes of dissolved inorganic nutrients: NH4+, NO2-, NO3-, PO4(3-) and Si(OH)4 from nearshore sediments of Gazi Bay were measured in situ within mangrove, seagrass and coral reef biotopes using benthic flux bell-jar chambers of cross-sectional area 0.066 m2 and volume 0.0132 m3. The objectives were: (1) to determine the influence of benthic fluxes, fluvial discharge and seasonal variations on the nutrient budget in the Bay waters; (2) to determine the effect of tidal and spatial variations on nutrient loads in the water column and (3) to establish the relative importance of the nutrient sources with regard to total community production of the Bay. The directly measured fluxes ranged from -270 to +148 micromol NH4+-N/m2/h; -60 to +63 micromol NO2(-)-N/m2/h; -79 to +41 micromol NO3(-)-N/m2/h; -79 to +75 micromol PO4(3-)-P/m2/h and +30 to +350 micromol Si(OH)4-Si/m2/h for and respectively. It was established that benthic fluxes are the major sources of dissolved inorganic NH4+, NO2- and Si(OH)4 while fluvial sources are important for NO3- and PO4(3-) into Gazi Bay waters. Seasonal variations had an appreciable effect on the PO4(3-) fluxes, N:Si ratio, river nutrient discharge, plankton productivity and important environmental factors such as salinity and temperature. Tidal and spatial variations had no significant effect on nutrient concentrations and net fluxes within the water column. The results imply that benthic fluxes are largely responsible for the nutrient dynamics of the nearshore coastal ecosystems especially where direct terrestrial inputs do not contribute significantly to the nutrient budget.

Ammonia↗
PubMed2005

Synthesis and ligand exchange reactions of P2Pd(II) and P2Pt(II) salicylaldimates.

Reaction of (dppe)MCl(2)(dppe = 1,2-bis(diphenylphosphino)ethane) with 2-(N-phenyliminomethyl)phenol leads to air-stable (dppe)M(N,O) chelates (M = Pd, 1a; M = Pt, 1b). The N-4-methylphenyl derivative of 1a has been characterized by X-ray analysis. The N,O ligands are kinetically labile and exchange occurs in solution in the presence of other salicylaldimines. In the presence of anilines, a metal-mediated imine exchange process occurs. Hammett analysis reveals that the platinum complexes are sensitive to the electronics at N but not at O. Electron donating groups on the N-aryl ring stabilize the metal complex.

Chelating Agents↗