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PubMed2001

Induction of aerobic peroxidation of liposomal membranes by bis(cyclopentadienyl)-vanadium(IV) (acetylacetonate) complexes.

The ability of bis(cyclopentadienyl)-vanadium(IV) (acetylacetonate) (1) to initiate oxygen-dependent lipid peroxidation in zwitterionic liposomal membranes was examined in detail. A comparison of the rates of the lipid peroxidation reaction demonstrated that the electron-donating capacity of the substituted acetylacetonate ligand significantly influences the rate of reaction. An increase in the rate of lipid peroxidation correlated to a decrease in the V(IV)/V(V) redox potential. Notably, lipid peroxidation initiated with 1 proceeded without the formation of radicals as shown by EPR spin trap techniques. In contrast, lipid peroxidation initiated with non-chelated bis(cyclopentadienyl)-vanadium(IV) dichloride (6) was associated with the production of radicals under similar experimental conditions. There also was a significant pH effect on the extent of peroxidation initiated with 6 versus the reaction initiated with 1. The mode of action of 1 likely involves the activation of molecular oxygen by the vanadium(IV) center followed by allylic hydrogen atom abstraction from the lipid.

Aerobiosis↗
PubMed2006

N-Nitroso products from the reaction of indoles with Angeli's salt.

While nitroxyl (HNO) has been shown to engage in oxidation and hydroxylation reactions, little is known about its nitrosating potential. We therefore sought to investigate the kinetics of formation and identity of the reaction products of the classical nitroxyl donor Angeli's salt (AS) with three representative tryptophan derivates (melatonin, indol-3-acetic acid, and N-acetyl-l-tryptophan) in vitro. In the presence of oxygen and at physiological pH, we find that the major products generated are the corresponding N-nitrosoindoles with negligible formation of oxidation and nitration products. A direct comparison of the effects of AS, nitrite, peroxynitrite, aqueous NO* solution, and the NO-donor DEA/NO toward melatonin revealed that nitrite does not participate in the reaction and that peroxynitrite is not an intermediate. Rather, N-nitrosoindole formation appears to proceed via a mechanism that involves electrophilic attack of HNO on the indole nitrogen, followed by a reaction of the intermediary hydroxylamine derivative with oxygen. Further in vivo experiments demonstrated that AS exhibits a unique nitrosation signature which differs from that of DEA/NO inasmuch as substantial amounts of a mercury-resistant nitroso species are generated in the heart, whereas S-nitrosothiols are the major reaction products in plasma. These data are consistent with the notion that the generation of nitroxyl in vivo gives rise to formation of nitrosative post-translational protein modifications in the form of either S- or N-nitroso products, depending on the redox environment. It is intriguing to speculate that the particular efficiency of nitroxyl to form N-nitroso species in the heart may account for the positive inotropic effects observed with AS earlier.

Animals↗
PubMed2001

A significant portion of mitochondrial proton leak in intact thymocytes depends on expression of UCP2.

The uncoupling protein homologue UCP2 is expressed in a variety of mammalian cells. It is thought to be an uncoupler of oxidative phosphorylation. Uncoupling proteins previously have been shown to be capable of translocating protons across phospholipid bilayers in proteoliposome systems. Furthermore, studies in mitochondria from yeast overexpressing the proteins have led to suggestions that they may act as uncouplers in cells. However, this issue is controversial, and to date, definitive experimental evidence is lacking as to whether UCP2 mediates part or all of the basal mitochondrial proton leak in mammalian cells in situ. In the present study, by using thymocytes isolated from UCP2-deficient and wild-type (WT) mice, we addressed the question whether UCP2 is directly involved in catalyzing proton leak in intact cells. Over a range of mitochondrial membrane potentials (DeltaPsi(m)), proton leak activity was lower in thymocytes from UCP2-deficient mice compared with WT mice. At physiological levels of DeltaPsi(m), a significant portion (50%) of basal proton leak in resting cells depended on UCP2. Of note, proton leak in whole cells from WT mice, but not UCP2-deficient mice, responded to stimulation by 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-napthalenyl)-1-propenyl]benzoic acid (TTNPB), a known activator of UCP2 activity. Consistent with the observed changes in proton leak, DeltaPsi(m) and ATP levels were increased in untreated thymocytes from UCP2-deficient mice. Interestingly, resting respiration was unaltered, suggesting that UCP2 function in resting cells may be concerned with the control of ATP production rather than substrate oxidation. This study establishes that UCP2, expressed at endogenous levels, mediates proton leak in intact cells.

Adenosine Triphosphate↗
PubMed2005

Structures of the ordered double perovskites Sr2YTaO6 and Sr2YNbO6.

The ordered perovskite Sr(2)YTaO(6), distrontium yttrium tantalum hexaoxide, has been reported as showing an unusual triclinic structure, at odds with the results from a recent group-theoretical analysis. A new investigation establishes that Sr(2)YTaO(6) and the isostructural Sr(2)YNbO(6), distrontium yttrium niobium hexaoxide, in fact both adopt the commonly occurring monoclinic structure, with the space-group symmetry P2(1)/n.

Calcium Compounds↗
PubMed1991

On the ability of lactoperoxidase to catalyze the peroxidase-oxidase oxidation of a vitamin E water-soluble derivative (Trolox C).

The rapid-scan spectral technique has been applied to test conversion of the lactoperoxidase compounds during the peroxidase-oxidase catalyzed oxidation of Trolox. The results clearly indicate a normal peroxidatic pathway of Trolox degradation. Changes of spectral scan profiles were investigated to study directly the interaction of Trolox with lactoperoxidase compound III. Oxygen radicals were not involved in peroxidase-mediated oxidation of Trolox. The rate of the one-electron reduction of lactoperoxidase compound I to II was the same in the absence and presence of equal amounts of Trolox and ascorbic acid, which is also a good substrate for lactoperoxidase. The oxidation of Trolox by lactoperoxidase has potential physiological relevance. Since it could help maintain the catalytic cycles and activity of animal peroxidases, leading to detoxification of hydrogen peroxide as a main product of inflammation processes.

Ascorbic Acid↗
PubMed1991

Mechanism of anoxic conduction block in mammalian nerve.

The mechanism by which anoxia blocks impulse conduction was studied in isolated sciatic nerves from the rat. The desheathed nerve was mounted in a recording chamber, and the compound action potential (CAP) was measured at controlled temperature (23 and 37 degrees C). When the nerve was irrigated with nitrogenated Ringer's solution compound action potential decreased to 50% in 10 min at 37 degrees C and in 35 min at 23 degrees C, whereas in oxygenated solution compound action potential decreased less than 5% in 60 min. A Na-free nitrogenated solution similarly caused anoxic block, that is the effect was independent of impulse activity. Ouabain (1 mM) decreased compound action potential by only ca. 4% in 30 min, and the effect of anoxia was delayed in presence of ouabain. Dinitrophenol (0.05 mM) reduced compound action potential to 50% in 5 min. These findings indicated that the anoxic block was not related to changes in axonal concentration of Na or K following impulse activity or inhibition of Na-K-ATPase. Instead the findings imply that the anoxic block is due to inactivation of Na-channels as a consequence of inhibition of another ATP-dependent process in the axon.

Action Potentials↗
PubMedDate not supplied

Combined biologic (anaerobic-aerobic) and chemical treatment of starch industry wastewater.

A combined biologic and chemical treatment of high-strength (total chemical oxygen demand [CODtot] up to 20 g/L), strong nitrogenous (total N up to 1 g/L), and phosphoric (total P up to 0.4 g/L) starch industry wastewater was investigated at laboratory-scale level. As a principal step for COD elimination, upflow anaerobic sludge bed reactor performance was investigated at 30 degrees C. Under hydraulic retention times (HRTs) of about 1 d, when the organic loading rates were higher than 15 g of COD/(L.d), the CODtot removal varied between 77 and 93%, giving effluents with a COD/N ratio of 4-5:1, approaching the requirements of subsequent denitrification. The activated sludge reactor operating in aerobic-anoxic regime (HRT of about 4 d, duration of aerobic and anoxic phases of 30 min each) was able to remove up to 90% of total nitrogen and up to 64% of COD tot from the anaerobic effluents under 17-20 degrees C. The coagulation experiments with Fe(III) showed that 1.4 mg of resting hardly biodegradable COD and 0.5 mg of phosphate (as P) could be removed from the aerobic effluents by each milligram of iron added.

Bacteria, Aerobic↗
PubMed2006

Analysis of secondary organic aerosol compounds from the photooxidation of d-limonene in the presence of NOx and their detection in ambient PM2.5.

Chemical analysis of secondary organic aerosol (SOA) from the photooxidation of a d-limonene/NOx/air mixture was carried out. SOA, generated in a smog chamber, was collected on Zefluor filters. To determine the structural characteristics of the compounds, the filter samples were solvent extracted and derivatized using analytical techniques that characterize functional groups contained in the compound: BF3-methanol derivatization was used for carboxylic groups, BSTFA for acidic and nonacidic hydroxyl groups, and PFBHA for ketone and aldehyde groups. The resulting derivative compounds were analyzed by GC-MS in the methane Cl and El modes. GC-MS analysis showed the occurrence of 103 oxygenated organic compounds in the filter extracts, 28 of which were identified. The major components include five tracer compounds previously identified from the photooxidation of alpha-pinene/NOx or beta-pinene/NOx systems, C4-C6 linear dicarboxylic acids, ketolimononaldehyde, limonic acid, and ketolimonic acid. Time profiles, yields, and proposed reaction schemes are provided for selected compounds. The laboratory SOA yield was 0.51 at a SOA concentration of 1470 microg m(-3). To determine the contributions of SOA products from d-limonene to ambient PM2.5, an analysis was performed for eight ambient PM2.5 samples collected in the southeastern United States in summer 2003. GC-MS analysis showed the occurrence of 21 d-limonene SOA compounds, indicating the impact of d-limonene on the regional aerosol burden. Based on our analysis, two compounds (nos. 55 and 69), not observed from the photooxidation of alpha-pinene or beta-pinene, are candidate tracers for d-limonene in atmospheric particulate matter.

Aerosols↗
PubMed2000

Approaches to wine aroma: release of aroma compounds from reactions between cysteine and carbonyl compounds in wine.

Under conditions close to those of wine, that is, low pH, aqueous medium, and low temperatures, this work examines the role of carbonyl (acetoin and acetol) and dicarbonyl (glyoxal, methylglyoxal, diacetyl, and pentane-2,3-dione) compounds associated with cysteine in the formation of odorous products. In particular, thiazole, 4-methylthiazole, 2-acetylthiazole, and trimethyloxazole and two sulfur and oxygenated heterocyclic compounds, 2-furanmethanethiol and thiophene-2-thiol, are examined. For thiophene-2-thiol, the reactional mechanism is proposed. Attempts were made to detect these compounds in wines from various origins. Certain molecules were identified for the first time in wine.

Cysteine↗
PubMed1983

Site and mechanism of covalent binding of 4-dimethylaminophenol to human hemoglobin, and its implications to the functional properties.

4-Dimethylaminophenol, after i.v. injection, rapidly forms ferrihemoglobin and has been successfully used in the treatment of cyanide poisoning. The catalytic ferrihemoglobin formation is terminated by thioether formation of oxidized 4-dimethylaminophenol with reduced glutathione or cysteine 93 beta of hemoglobin. Hereby the physiological functions of human hemoglobin are markedly altered. After binding of two molecules of 4-dimethylaminophenol to tetrameric hemoglobin, the rate of autoxidation is increased about 6-fold. The oxygen affinity is 10 times higher than normal, the Hill coefficient is diminished nearly to unity, and the Bohr effect is reduced by about 50%. The physiologically important allosteric regulation of the oxygen affinity by 2,3-diphosphoglycerate is abolished, and the binding of 2,3-diphosphoglycerate to deoxyhemoglobin no longer functions. By molecular sieving, two alkylated hemoglobins were separated: a hemoglobin fraction with an unchanged low tetramer dimer dissociation, normal electronic spectra, and normal digestibility by carboxypeptidase A; and a second fraction with a high degree of dissociation, altered electronic spectra, and impaired digestibility. A tryptic peptide was isolated containing cysteine 93 beta and histidine 146 beta cross-linked by an arylic compound missing the dimethylamine label. The following reaction mechanism is concluded: Oxy-hemoglobin catalyzes the oxidation of 4-dimethylaminophenol, and the oxidation product, presumably N,N-dimethylquinonimine, is bound covalently to cysteine 93 beta by a thioether linkage. This adduct is unstable and autoxidizes further with the liberation of dimethylamine. The resulting quinoid thioether electrophilically attacks the COOH-terminal histidine of the beta-chain, thereby forming an intramolecular cross-link. By this latter reaction, hemoglobin lacks allosteric transition upon ligation and is obviously frozen in its quaternary R-state.

Aminophenols↗
PubMed1986

Horseradish peroxidase catalyzed hydroxylations: mechanistic studies.

The hydroxylation of phenol to hydroquinone and catechol in the presence of dihydroxyfumaric acid and oxygen catalyzed by horseradish peroxidase was studied under conditions where the product yield was high and the side reactions were minimal. The reaction is partially uncoupled with a molar ratio of dihydroxyfumaric acid consumed to hydroxylated products of 12:1. Hydrogen peroxide does not participate in the reaction as evidenced by the lack of effect of catalase and by the direct addition of hydrogen peroxide. Conversely, superoxide and hydroxyl radicals are involved as their scavengers are potent inhibitors. Experiments were all consistent with the involvement of compound III (oxygenated ferrous complex) of peroxidase in the reaction. Compound III is stable in the presence of phenol alone but decomposes rapidly in the presence of both phenol and dihydroxyfumaric acid with the concomitant formation of product. Therefore, phenol and dihydroxyfumaric acid must be present with compound III in order for the hydroxylation reaction to occur. A mechanism consistent with the experimental results is proposed.

Animals↗
PubMed2006

Pharmacological MRI of stem cell transplants in the 3-nitropropionic acid-damaged striatum.

Blood oxygen level dependent (BOLD) pharmacological magnetic resonance imaging (phMRI) affords the non-invasive visualization of brain activity resulting from the administration of pharmacological compounds. Once the compound-responsive cells are lost, no change in activity is expected to occur. This principle therefore allows the assessment of neuronal loss or lack of signal transmission. These investigations can provide evidence of pathology in the absence of significant tissue loss and can be highly specific to determine which type of cell has been lost. Conversely, transplantation of cells replacing the lost neurons should restore normal signal transmission. We here demonstrate the application of phMRI to differentiate between rats with 3-nitroproprionic acid (3-NPA)-induced striatal lesions and 3-NPA-lesioned animals with neural stem cell transplants or controls. 3-NPA-induced lesions mainly involve striatal projection neurons that are responsive to dopamine agonists. The D2-agonist bromocriptine acts on these projection cells and loss of these through 3-NPA administration resulted in a significant decrease of locomotor activity and a substantial attenuation of the BOLD-response in the striatum. In contrast, lesioned animals that were grafted with neural stem cells exhibited an activity pattern akin to controls. Hence, grafting of neural stem cells exerts a functionally significant effect on striatal signal transmission that could underpin behavioral recovery.

Animals↗
PubMed2000

Quenching of singlet oxygen (1deltag) by cobalt complexes with four nitrogen atoms in the equatorial plane.

The quenching of singlet oxygen (1deltag) by cobalt(III)-bis-1,2-benzosemiquinone-diiminato complexes (general structure LCo(111)(BQDI)2ClO4) has been studied in different solvents by measuring the singlet oxygen phosphorescence decay in time-resolved experiments. The axial ligand (Ph3As, Ph3Sb, N-methyl-imidazole, pyrrolidine) has practically no influence on the quenching; however, the chlorinated benzosemiquinone-diiminato complex has a markedly lower quenching rate constant. The solvent effects can be fully explained by the difference in viscosity, which supports the assumption that the quenching is diffusion controlled. The reactive radius of the encounter pair has been estimated to be 0.3 nm, shorter than the radius of the complex itself, which points to the fact that singlet oxygen must approach the central cobalt atom at the (partially) open axial position. The significance of these results regarding the quenching of singlet oxygen by vitamin B12 derivatives is discussed.

Cobalt↗