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1.
Cytochrome P-450 from liver microsomes of phenobarbital-treated rabbits catalyzed anaerobic dehalogenation of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) when combined with NADPH and NADPH-cytochrome P-450 reductase. Cytochromes P-450B1 and P-448 from liver microsomes of untreated rabbits were less active. Triton X-100 accelerated the reaction. Unlike anaerobic dehalogenation of halothane in microsomes, the major product was 2-chloro-1,1,1-trifluoroethane and 2-chloro-1,1-difluoroethylene was negligible. These products were not detected under aerobic conditions, and dehalogenation activity was inhibited by carbon monoxide, phenyl isocyanide and metyrapone.  相似文献   

2.
To study the modulation of the reductive metabolism of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) by microsomal cytochrome b5, formation of 2-chloro-1,1,1-trifluoroethane (CTE) and 2-chloro-1,1-difluoroethylene (CDE), major reduced metabolites of halothane, was analyzed in vivo and in vitro. Rats were pretreated with both malotilate (diisopropyl-1,3-dithiol-2-ylidenemalonate) and sodium phenobarbital (malotilate-treated rats) or only with sodium phenobarbital (control rats). The microsomes of malotilate-treated rats had significantly more cytochrome b5 than the controls, whereas the cytochrome P-450 content was not different between the two groups. At the end of 2-h exposure to 1% halothane in 14% oxygen, the ratio of CDE to CTE in arterial blood was significantly higher in malotilate-treated rats than in the controls. Under anaerobic conditions, the formation of CDE and the ratio of CDE to CTE were significantly greater in microsomal preparations of malotilate-treated rats than those of the controls. In a reconstituted system containing cytochrome P-450PB purified from rabbit liver, addition of cytochrome b5 to the system enhanced the formation of CDE and increased the ratio of CDE to CTE. These results suggested that cytochrome b5 enhances the formation ratio of CDE to CTE by stimulating the supply of a second electron to cytochrome P-450, which might reduce radical reactions in the reductive metabolism of halothane.  相似文献   

3.
《Free radical research》2013,47(2):77-82
Intact rat lenses incubated with lumazine and xanthine oxidase are physiologically damaged as evidenced by a decrease in the net accumulation of rubidium ions against a concentration gradient. Superoxide dismutase protected the tissue against this damage. These experiments, therefore, demonstrate the susceptibility of the lens tissue to O2?? injury under ambient and nonphotochemical conditions, suggesting a possible implication of this radical in the tissue in vivo and eventual cataract formation. The lumazine/xanthine oxidase system which is known to cause oxygen reduction predominantly by the monovalent route, producing superoxide, appears quite suitable to evaluate the toxicity of O2?? to the tissues in vitro.  相似文献   

4.
Orthophosphate is rapidly transported into cultured cells and subsequently incorporated into numerous compounds. A high-performance liquid chromatographic method that enables the measurement of 32Pi incorporation into acid-soluble metabolites in cultured cells treated with exogenous 32Pi is described. Baseline resolution and quantitative recovery of 12 ribonucleotides are accomplished in less than 75 min. In cultured, beating rat heart cells, the concentration and extent of labeling by 32Pi of most phosphorylated metabolites were unchanged in cells treated with the anesthetic halothane (2-bromo-2-chloro-1,1,1-trifluoroethane). The method is generally applicable to the investigation of phosphate transport and incorporation by numerous cell types under various experimental conditions.  相似文献   

5.
NADPH reduced rabbit liver microsomal enzymes catalyzed anaerobic dehalogenation of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) to produce CF2CHCl and CF3CH2Cl. Anaerobic dehalogenation was optimal at pH7.4 and was blocked by either oxygen or carbon monoxide. The degree of inhibition of anaerobic dehalogenation by carbon monoxide was closely correlated to the proportion of carbon monoxide complex of cytochrome P450. Anaerobic dehalogenation was enhanced by pretreatment of the animals with phenobarbital but not with methylcholanthrene.  相似文献   

6.
Gerald T. Babcock  Kenneth Sauer 《BBA》1975,376(2):329-344
Rapid light-induced transients in EPR Signal IIf (F?+) are observed in 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-treated, Tris-washed chloroplasts until the state F P680 Q? is reached. In the absence of exogenous redox mediators several flashes are required to saturate this photoinactive state. However, the Signal IIf transient is observed on only the first flash following DCMU addition if an efficient donor to Signal IIf, phenylenediamine or hydroquinone, is present. Complementary polarographic measurements show that under these conditions oxidized phenylenediamine is produced only on the first flash of a series. The DCMU inhibition of Signal IIf can be completely relieved by oxidative titration of a one-electron reductant with E08.0 = +480 mV. At high reduction potentials the decay time of Signal IIf is constant at about 300 ms, whereas in the absence of DCMU the decay time is longer and increases with increasing reduction potential.A model is proposed in which Q?, the reduced Photosystem II primary acceptor, and D, a one-electron 480 mV donor endogenous to the chloroplast suspension, compete in the reduction of Signal IIf (F?+). At high potentials D is oxidized in the dark, and the (Q? + F?+) back reaction regenerates the photoactive F P680 Q state. The electrochemical and kinetic evidence is consistent with the hypothesis that the Signal IIf species, F, is identical with Z, the physiological donor to P680.  相似文献   

7.
The reactions of AuBr?4 and Au(CN)2Br?2 with uracil in water produce gold(I) and 5-bromouracil and/or 5-bromo-6-hydroxy-5,6-dihydrouracil. The observed kinetics of the reactions are consistent with a mechanism involving a fast redox pre-equilibrium followed by bromination of the pyrimidine (X?= Br? or CN?):
The calculated equilibrium constant K = k1/k?1 is 1.6 × 10?10 M for AuBr?4 and 1.7 × 10?11 M for Au(CN)2Br?2. Specific rates for the reduction of AuBr?4 are correspondingly greater than those for the reduction of Au(CN)2Br?2.  相似文献   

8.
《Free radical research》2013,47(6):359-369
Spin trapping techniques have been used to detect free radicals generated from the in vitro metabolism by rat liver microsomes of carbon tetrachloride (CCl4) and bromotrichloromethane (BrCCI) under conditions of varying oxygen tension and pH. Dispersions of rat liver microsomes incubated with 12CCl4, 13CCl4 or Br12CCl3, α-phenyl-tert-butyl nitrone (PBN) and NADPH/NADH in a phosphate buffer varying in pH from 6.6 to 8.0 under varying oxygen tensions produced various amounts of four different PBN adducts: PBN-CCl3, PBN-L, PBN-OL and PBN-CO?2 where L is a carbon-centered lipid type radical and LO is an oxygen-centered lipid type radical. The relative amount of PEN-CO; increases with the absence of oxygen. With the use of 31P-NMR in vivo spectroscopy it was possible to detect a pH change from 7.4 to 6.8 in the livers of rats treated with CCl4, or BrCCl3. These results suggest that halocarbon metabolism in biological systems may depend on both oxygen tension as well as pH.  相似文献   

9.
Bromoperoxidases were found in coralline algae (Corallinaceae, Rhodophyta) collected from seasides in Japan, and high enzyme activities were observed in Corallina officinalis, Corallina pilulifera and Amphiroa zonata. The optimum pHs of the enzymes from coralline algae were around 6.0. The enzymes were specific for I? and Br?, and did not act on Cl? and F?. The enzymes purified from Corallina pilulifera and Amphiroa ephedraea catalyzed the brominations of phenol and O-hydroxybenzyl alcohol in the presence of Br? and H202 to form the same product, 2,4,6-tribromophenol.  相似文献   

10.
Hiroshi Seki  Masashi Imamura 《BBA》1981,635(1):81-89
The reactions of ferrocytochrome c with Br?2, (SCN)?2, N3 and OH radicals were followed by measuring the change in the optical spectra of cytochrome c on γ-irradiation as well as the rate of change of absorbance upon pulse irradiation.Ferrocytochrome c is oxidized to ferricytochrome c by Br?2, (SCN)?2 or N3 radical with an efficiency of about 100% through a second-order process in which no intermediates were observed. The rate constants in neutral solutions at I = 0.073 are 9.7 · 108 M?1 · s?1, 7.9 · 108 M?1 · s?1, 1.3 · 109 M?1 · s?1 for the oxidation by Br?2, (SCN)?2 and N3 radicals, respectively. The rate constants do not vary appreciably in alkaline solutions (pH 8.9). The ionic strength dependence was observed for the rate constants of the oxidation by Br?2 and (SCN)?2. Those rate constants estimated on the assumption that the radicals react only with the amino acid residues with the characteristic steric correction factors were less than one-tenth of the observed ones. These results suggest that the partially exposed region of the heme is the probable site of electron transfer from ferrocytochrome c to the radical.Hydroxyl radicals also oxidize ferrocytochrome c with a high rate constant (k > 1 · 1010 M?1 · s?1), but with a very small efficiency (5%).  相似文献   

11.
W. Kaiser  W. Urbach 《BBA》1976,423(1):91-102
1. Dihydroxyacetone phosphate in concentrations ? 2.5 mM completely inhibits CO2-dependent O2 evolution in isolated intact spinach chloroplasts. This inhibition is reversed by the addition of equimolar concentrations of Pi, but not by addition of 3-phosphoglycerate. In the absence of Pi, 3-phosphoglycerate and dihydroxyacetone phosphate, only about 20% of the 14C-labelled intermediates are found in the supernatant, whereas in the presence of each of these substances the percentage of labelled intermediates in the supernatant is increased up to 70–95%. Based on these results the mechanism of the inhibition of O2 evolution by dihydroxyacetone phosphate is discussed with respect to the function of the known phosphate translocator in the envelope of intact chloroplasts.2. Although O2 evolution is completely suppressed by dihydroxyacetone phosphate, CO2 fixation takes place in air with rates of up to 65μ mol · mg?1 chlorophyll · h?1. As non-cyclic electron transport apparently does not occur under these conditions, these rates must be due to endogenous pseudocyclic and/or cyclic photophosphorylation.3. Under anaerobic conditions, the rates of CO2 fixation in presence of dihydroxyacetone phosphate are low (2.5–7 μmol · mg?1 chlorophyll · h?1), but they are strongly stimulated by addition of dichlorophenyl-dimethylurea (e.g. 2 · 10?7 M) reaching values of up to 60 μmol · mg?1 chlorophyll · h?1. As under these conditions the ATP necessary for CO2 fixation can be formed by an endogenous cyclic photophosphorylation, the capacity of this process seems to be relatively high, so it might contribute significantly to the energy supply of the chloroplast. As dichlorophenyl-dimethylurea stimulates CO2 fixation in presence of dihydroxyacetone phosphate under anaerobic but not under aerobic conditions, it is concluded that only under anaerobic conditions an “overreduction” of the cyclic electron transport system takes place, which is removed by dichlorophenyl-dimethylurea in suitable concentrations. At concentrations above 5 · 10?7 M dichlorophenyl-dimethylurea inhibits dihydroxyacetone phosphate-dependent CO2 fixation under anaerobic as well as under aerobic conditions in a similar way as normal CO2 fixation. Therefore, we assume that a properly poised redox state of the electron transport chain is necessary for an optimal occurrence of endogenous cyclic photophosphorylation.4. The inhibition of dichlorophenyl-dimethylurea-stimulated CO2 fixation in presence of dihydroxyacetone phosphate by dibromothymoquinone under anaerobic conditions indicates that plastoquinone is an indispensible component of the endogenous cyclic electron pathway.  相似文献   

12.
Titanium dioxide (TiO2) nanoparticles have been shown to be genotoxic to cells exposed to ultraviolet A (UVA) radiation. Using the technique of electron spin resonance (ESR) spin trapping, we have confirmed that the primary damaging species produced on irradiation of TiO2 nanoparticles is the hydroxyl (OH) radical. We have applied this technique to TiO2-treated fish and mammalian cells under in vitro conditions and observed the additional formation of carboxyl radical anions (CO2?) and superoxide radical anions (O2?). This novel finding suggests a hitherto unreported pathway for damage, involving primary generation of OH radicals in the cytoplasm, which react to give CO2? radicals. The latter may then react with cellular oxygen to form O2? and genotoxic hydrogen peroxide (H2O2).  相似文献   

13.
Hypobromous acid (HOBr) is formed by eosinophil peroxidase and myeloperoxidase in the presence of H2O2, Cl?, and Br? in the host defense system of humans, protecting against invading bacteria. However, the formed HOBr may cause damage to DNA and its components in the host. When a guanine nucleoside (3′,5′-di-O-acetyl-2′-deoxyguansoine) was treated with HOBr at pH 7.4, spiroiminodihydantoin, guanidinohydantoin/iminoallantoin, dehydro-iminoallantoin, diimino-imidazole, amino-imidazolone, and diamino-oxazolone nucleosides were generated in addition to an 8-bromoguanine nucleoside. The major products were spiroiminodihydantoin under neutral conditions and guanidinohydantoin/iminoallantoin under mildly acidic conditions. All the products were formed in the reaction with HOCl in the presence of Br?. These products were also produced by eosinophil peroxidase or myeloperoxidase in the presence of H2O2, Cl?, and Br?. The results suggest that the products other than 8-bromoguanine may also have importance for mutagenesis by the reaction of HOBr with guanine residues in nucleotides and DNA.  相似文献   

14.
Ionizing radiation has been found to induce stable defects in the crystalline lattice of bone mineral hydroxyapatite, defined as CO2 ? radical ions possessing spins. The purpose of our study was to evaluate CO2 ? radical ions induced in non-defatted or defatted human compact bone by gamma radiation (G) and accelerated electron beam (EB), applied with two doses at different temperatures. Moreover, the potential effect of free radical ion formation on mechanical parameters of compact bone, tested under compression in the previous studies, was evaluated. Bone rings from femoral shafts of six male donors (age 51 ± 3 years) were collected and assigned to sixteen experimental groups according to different processing methods (non-defatted or defatted), G and EB irradiation dose (25 or 35 kGy), and irradiation temperature [ambient temperature (AT) or dry ice (DI)]. Untreated group served as control. Following grinding under LN2 and lyophilization, CO2 ? radical ions in bone powder were measured by electron paramagnetic resonance spectrometry. We have found that irradiation of bone with G and EB induces formation of enormous amounts of CO2 ? radical ions, absent from native tissue. Free radical ion formation was dose-dependent when irradiation was performed at AT, and significantly lower in EB as compared to G-irradiated groups. In contrast, no marked effect of dose was observed when deep-frozen (DI) bone samples were irradiated with G or EB, and free radical ion numbers seemed to be slightly higher in EB-irradiated groups. Irradiation at AT induced much higher quantities of CO2 ? radical ions then on DI. That effect was more pronounced in G-irradiated bone specimens, probably due to longer exposure time. Similarly, bone defatting protective effect on free radical ion formation was found only in groups irradiated for several hours with gamma radiation at ambient temperature. Ambient irradiation temperature together with exposure time seem to be key parameters promoting CO2 ? radical ion formation in bone mineral and may mask the opposite effect of defatting and the possible effect of irradiation type. Significant weak negative correlations between CO2 ? radical ion number and some mechanical properties of compact bone rings (Young’s modulus and ultimate stress) were found.  相似文献   

15.
Inhibition of photosynthesis after exposure to solar radiation was investigated in the marine green alga Dunaliella salina by monitoring photosynthetic optimal quantum yield Fv/Fm and efficiency of oxygen production. Samples were exposed to solar radiation in Ancient Korinth, Greece (37°58′ N, 23°0′ E) in August 1994. Within 30 min, Fv/Fm and efficiency of oxygen production decreased with similar kinetics with increasing exposure time. The inhibition, however, diminished when ultraviolet radiation was progressively excluded by means of colour filter glasses. Samples exposed for 3 h showed complete or partial recovery of photosynthesis, with almost the same rate under all irradition conditions. The fit of the experimental data with an analytical model describing inhibition of photosynthesis as a function of a linear combination of the photon fluence in the UV-B, UV-A and PAR allows one to estimate the relative mean effectiveness for inhibition by the three spectral ranges [about 2 × 10?4, 4 × 10?6 and 2 × 10?7 (μmol photons m?2)?1 for UV-B, UV-A and PAR, respectively].  相似文献   

16.
In the presence of Cl?, the severity of ammonia-induced inhibition of photosynthetic oxygen evolution is attenuated in spinach thylakoid membranes (Sandusky, P.O. and Yocum, C.F. (1983) FEBS Lett. 162, 339–343). A further examination of this phenomenon using steady-state kinetic analysis suggests that there are two sites of ammonia attack, only one of which is protected by the presence of Cl?. In the case of Tris-induced inhibition of oxygen evolution only the Cl? protected site is evident. In both cases the mechanism of Cl? protection involves the binding of Cl? in competition with the inhibitory amine. Anions (Br? and NO?3) known to reactive oxygen evolution in Cl?-depleted membranes also protect against Tris-induced inhibition, and reactivation of Cl?-depleted membranes by Cl? is competitively inhibited by ammonia. Inactivation of the oxygen-evolving complex by NH2OH is impeded by Cl?, whereas Cl? does not affect the inhibition induced by so-called ADRY reagents. We propose that Cl? functions in the oxygen-evolving complex as a ligand bridging manganese atoms to mediate electron transfer. This model accounts both for the well known Cl? requirement of oxygen evolution, and for the inhibitory effects of amines on this reaction.  相似文献   

17.
In this study, chlorophyll fluorescence parameters (?F/F m′, F v/F m) and oxygen evolution of female vegetative tissues of Porphyra katadai var. hemiphylla in unisexual culture (FV) and in mixed culture with male vegetative tissues (FV-M) were followed at 5–20 °C, 10 and 80 μmol photons m?2 s?1. The formation of reproductive tissues was closely correlated with decreasing photosynthetic activities. At the same temperature the tissues cultured under 80 μmol photons m?2 s?1 showed a greater extent of maturation than those under 10 μmol photons m?2 s?1, and their decrease in photosynthesis was also larger. Under the same light intensity the extent of maturation increased with increasing temperature, and both cultures showed higher values of ?F/F m′ and F v/F m at 10 and 15 °C, while their oxygen evolution became negative at 15–20 °C during the later period. Under the same culture condition the maturation of FV-M culture was relatively faster than that of FV culture, while their photosynthetic activity, especially ?F/F m′, was lower.  相似文献   

18.
The effect of different co-anions on the formation and aggregation of the ordered structure of the anionic polysaccharide kappa-carrageenan has been investigated by optical rotation, differential scanning calorimetry, and halide-n.m.r. spectroscopy. The mid-point temperature (Tm) of the disorder—order transition increases systematically with the Hofmeister number for the anion through the lyotropic series SO42? < F? < Cl? < Br? < NO3? < I? < SCN? when salt concentration and cation (Me4N+ or K+) are held constant. A corresponding increase is observed in transition enthalpy (ΔHcal) and entropy (ΔScal). Helix—helix aggregation (as indicated by turbidity, gel formation, and hysteresis between heating and cooling scans) also shows a systematic dependence on the Hofmeister number for the anion, but in the opposite sense. Thus, with tetramethylammonium as the sole counterion present, clear solutions with no thermal hysteresis in the order—disorder transition are observed at all temperatures with I?, Br?, NO3?, or Cl? as co-anion, whereas weak, turbid gels with significant thermal hysteresis between melting and setting are formed in the presence of SO42?, and to a lesser degree F?. With K+ as counterion, a similar regular progression is observed through the anion lyotropic series from rapid formation of very turbid gels in the presence of F?, to very slow development of clear gels with I? or SCN?. In agreement with previous studies, an increase in 127I-n.m.r. linewidth was observed on conformational ordering of kappa-carrageenan (Me4N+ salt form) in the presence of Me4NI. However, closely similar behaviour was observed for 35Cl and 81Br, indicating a simple charge-cloud interaction rather than the specific site-binding of I? which has previously been suggested.  相似文献   

19.
This study investigated the influence of inorganic salts on enzymatic activity and the removal of trace organic contaminants (TrOCs) by crude laccase from the white-rot fungus Pleurotus ostreatus. A systematic analysis of 15 cations and anions from common inorganic salts was presented. Laccase activity was not inhibited by monovalent cations (i.e. Na+, NH4+, K+), while the presence of divalent and trivalent cations showed variable impact – from negligible to complete inhibition – of both laccase activity and its TrOC removal performance. Of interest was the observation of discrepancy between residual laccase activity and TrOC removal in the presence of some ions. Mg2+ had negligible impact on residual laccase activity but significant impact on TrOC removal. Conversely, F? showed greater impact on residual laccase activity than on TrOC removal. This observation indicated different impacts of the interfering ions on the interaction between laccase and TrOCs as compared to that between laccase and the reagent used to measure its activity, implicating that residual laccase activity may not always be an accurate indicator of TrOC removal. The degree of impact of halides was in the order of F??>?I? >?Br??>?Cl?. Particularly, the tolerance of the tested laccase to Cl? has important implications for a range of industrial applications.  相似文献   

20.
Replacing oxygen (O2) with air is a critical step in the development of lithium (Li)–air batteries. A trace amount of carbon dioxide (CO2) in the air is, however, influentially involved in the O2 chemistry, which indicates that a fundamental understanding of the effect of CO2 is required for the design of practical cells. When up to 30% CO2 is added to Li–O2 cells, CO2 acts as an O2? scavenger. Their chemical reactions form soluble products, CO42? and C2O62?, in the tetraglyme electrolyte solution, and enhance full capacity and cell cyclability. A critical challenge is, however, the sluggish decomposition of the coproduct Li2CO3 during recharge. To lower the charging overpotential, a Br3?/Br2 redox couple is incorporated and its redox behavior is investigated using spectroscopic methods. The redox shuttle of Br3?/Br2 decomposes amorphous Li2CO3 more efficiently than its crystalline counterpart. It is revealed that Br2 combines with Br3? to form a Br2···Br3? complex, which acts as a mobile catalyst in the electrolyte solution without swift precipitation of the nonpolar Br2. This comprehensive study, revealing the molecular structure and redox process of mobile catalysts, provides an insight into improving the design of redox couples toward superior cycling performance.  相似文献   

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