共查询到20条相似文献,搜索用时 15 毫秒
1.
《Free radical research》2013,47(4):241-253
We have evaluated the abilities of ferulic acid, (±) catechin, (+) catechin and (-) epicatechin to scavenge the reactive oxygen species hydroxyl radical (OH±), hypochlorous acid (HOCl) and peroxyl radicals (RO2).Ferulic acid tested at concentrations up to 5 mM inhibited the peroxidation of phospholipid liposomes. Both (±) and (+) catechin and (-) epicatechin were much more effective. All the compounds tested reacted with trichloromethyl peroxyl radical (CCl3O2) with rate constants > 1 × 106M?1s?1.A mixture of FeCl3-EDTA, hydrogen peroxide (H2O2) and ascorbic acid at pH 7.4, has often been used to generate hydroxyl radicals (OH.) which are detected by their ability to cause damage to the sugar deoxyribose. Ferulic acid, (+) and (±) catechin and (-) epicatechin inhibited deoxyribose damage by reacting with OH. with rate constants of 4.5 × 109M?1s?1, 3.65 × 109M?1s?1, 2.36 × 109M?1s?1 and 2.84 × 109M?1s?1 respectively. (-) Epicatechin, ferulic acid and the (+) and (±) catechins exerted pro-oxidant action, accelerating damage to DNA in the presence of a bleomycin-iron complex. On a molar basis, ferulic acid was less effective in causing damage to DNA compared with the catechins.A mixture of hypoxanthine and xanthine oxidase generates O2 which reduces cytochrome c to ferrocytochrome c. (+) Catechin and (-) epicatechin inhibited the reduction of cytochrome c in a concentration dependent manner. Ferulic acid and (±) catechin had only weak effects.All the compounds tested were able to scavenge hypochlorous acid at a rate sufficient to protect alpha-1-antiproteinase against inactivation. Our results show that catechins and ferulic acid possess antioxidant properties. This may become important given the current search for “natural” replacements for synthetic antioxidant food additives. 相似文献
2.
J.E. Packer J.S. Mahood V.O. Mora-Arellano T.F. Slater R.L. Willson B.S. Wolfenden 《Biochemical and biophysical research communications》1981,98(4):901-906
The ‘singlet oxygen scavengers’. 1,4-diazobicyclo(2,2,2)-octane (DABCO), diphenyl furan and β-carotene react rapidly with the organic peroxyradical CCl3O2?. The absolute reaction rate constants k = 1.2 ± 0.2 × 107, 6 ± 2 × 107 at 1.5 ± 0.2 × 109 M?1s?1 respectively have been determined by pulse radiolysis. Comparison with other data suggest that other free radicals are also likely to react with these compounds; in the case of the hydroxyl radical and DABCO k = 1.25 × 109 M?1s?1 has been determined. 相似文献
3.
《Free radical research》2013,47(4-6):259-270
Using the pulse radiolysis technique, we have demonstrated that bleomycin-Fe(III) is stoichiometrically reduced by CO2? to bleomycin-Fe(II) with a rate of (1.9 ± 0.2) × 108M?1s?1. In the presence of calf thymus DNA, the reduction proceeds through free bleomycin-Fe(III) and the binding constant of bleomycin-Fe(III) to DNA has been determined to be (3.8 ± 0.5) x 104 M?1. It has also been demonstrated that in the absence of DNA O2?1 reacts with bleomycin-Fe(III) to yield bleomycin-Fe(II)O2, which is in rapid equilibrium with molecular oxygen, and decomposes at room temperature with a rate of (700 ± 200) s?1. The resulting product of the decomposition reaction is Fe(III) which is bound to a modified bleomycin molecule. We have demonstrated that during the reaction of bleomycin-Fe(II) with O2, modification or self-destruction of the drug occurs, while in the presence of DNA no destruction occurs, possibly because the reaction causes degradation of DNA. 相似文献
4.
C Houée-Levin M Gardès-Albert C Ferradini J Pucheault 《Biochemical and biophysical research communications》1979,91(3):1196-1200
The reduction of alloxan (A) into dialuric acid (AH2) by?COO? radical has been investigated by pulse-radiolysis. A radical intermediate ?AH is shown to be formed with a rate constant k (?COO? + A) = 3.2 × 107 M?1 s?1. ?AH absorption spectrum is given. This radical disappears by disproportionation leading to dialuric acid, with a rate constant 2 k = 1.6 × 108 M?1s?1. 相似文献
5.
E Cadenas A Boveris C I Ragan A O Stoppani 《Archives of biochemistry and biophysics》1977,180(2):248-257
Complex I (NADH-ubiquinone reductase) and Complex III (ubiquinol-cytochrome c reductase) supplemented with NADH generated O2? at maximum rates of 9.8 and 6.5 nmol/min/mg of protein, respectively, while, in the presence of superoxide dismutase, the same systems generated H2O2 at maximum rates of 5.1 and 4.2 nmol/min/mg of protein, respectively. H2O2 was essentially produced by disproportionation of O2?, which constitutes the precursor of H2O2. The effectiveness of the generation of oxygen intermediates by Complex I in the absence of other specific electron acceptors was 0.95 mol of O2? and 0.63 mol of H2O2/mol of NADH. A reduced form of ubiquinone appeared to be responsible for the reduction of O2 to O2?, since (a) ubiquinone constituted the sole common major component of Complexes I and III, (b) H2O2 generation by Complex I was inhibited by rotenone, and (c) supplementation of Complex I with exogenous ubiquinones increased the rate of H2O2 generation. The efficiency of added quinones as peroxide generators decreased in the order Q1 > Q0 > Q2 > Q6 = Q10, in agreement with the quinone capacity of acting as electron acceptor for Complex I. In the supplemented systems, the exogenous quinone was reduced by Complex I and oxidized nonenzymatically by molecular oxygen. Additional evidence for the role of ubiquinone as peroxide generator is provided by the generation of O2? and H2O2 during autoxidation of quinols. In oxygenated buffers, ubiquinol (Q0H2), benzoquinol, duroquinol and menadiol generated O2? with k3 values of 0.1 to 1.4 m? · s?1 and H2O2 with k4 values of 0.009 to 4.3 m?1 · s?1. 相似文献
6.
The superfamily of heme?copper oxidoreductases (HCOs) include both NO and O2 reductases. Nitric oxide reductases (NORs) are bacterial membrane enzymes that catalyze an intermediate step of denitrification by reducing nitric oxide (NO) to nitrous oxide (N2O). They are structurally similar to heme?copper oxygen reductases (HCOs), which reduce O2 to water. The experimentally observed apparent bimolecular rate constant of NO delivery to the deeply buried catalytic site of NORs was previously reported to approach the diffusion-controlled limit (108–109?M?1?s?1). Using the crystal structure of cytochrome-c dependent NOR (cNOR) from Pseudomonas aeruginosa, we employed several protocols of molecular dynamics (MD) simulation, which include flooding simulations of NO molecules, implicit ligand sampling and umbrella sampling simulations, to elucidate how NO in solution accesses the catalytic site of this cNOR. The results show that NO partitions into the membrane, enters the enzyme from the lipid bilayer and diffuses to the catalytic site via a hydrophobic tunnel that is resolved in the crystal structures. This is similar to what has been found for O2 diffusion through the closely related O2 reductases. The apparent second order rate constant approximated using the simulation data is ~5?×?108?M?1?s?1, which is optimized by the dynamics of the amino acid side chains lining in the tunnel. It is concluded that both NO and O2 reductases utilize well defined hydrophobic tunnels to assure that substrate diffusion to the buried catalytic sites is not rate limiting under physiological conditions. 相似文献
7.
T Araiso H B Dunford C K Chang 《Biochemical and biophysical research communications》1979,90(2):520-524
Recombination of apo horseradish peroxidase with 2,4 dimethyldeutero hemin and its mono- and dimethyl esters was performed. The number of free carboxyl side chains in these three hemins is 2, 1 and 0 respectively. Despite such a difference, all of these three reconstituted enzymes can react with H2O2 to produce compound I. The second order rate constants for compound I formation are 1.3 × 107 M?1s?1, 8.5 × 106 M?1s?1 and 5.9 × 106 M?1s?1. Therefore the propionate side chain of hemin has no direct role in compound I formation. 相似文献
8.
A reaction of the superoxide radical with tetrapyrroles 总被引:1,自引:0,他引:1
Bilirubin and biliverdin were bleached during exposure to the aerobic xanthine oxidase reaction. Enzymic scavenging of O2?, by Superoxide dismutase, inhibited, whereas enzymic scavenging of H2O2, by catalase, did not. Increasing the rate of production of O2? without increasing the turnover rate of xanthine oxidase, by increasing pO2, accelerated the bleaching of the biliverdin. Moreover, a scavenger of OH·, such as benzoate, or an inactivating chelating agent for iron, such as diethylenetriamine pentaacetate or desferrioxamine mesylate, did not inhibit. It follows that O2? can directly attack these tetrapyrroles. Kinetic competition between Superoxide dismutase and bilirubin yielded a value for kbilirubin, O2? = 2.3 × 104 M?1s?1 at pH 8.3 and at 23 °C. A similar experiment for biliverdin yielded a value for kbilirubin, O2? = 7 × 104 M?1s?1. 相似文献
9.
Robert Presswood J.W. Hastings 《Biochemical and biophysical research communications》1978,82(3):990-996
Upon reaction of luciferase-FMNH2 with oxygen a complex series of absorbance changes occur, leading to the formation of a stable ( about 35 min at 2°) dihydroflavin peroxyluciferase intermediate. Observed at 380, 445, or 600 nm, there is first a rapid absorbance increase which is oxygen-concentration dependent (k ? 106 M?1s?1. Following this there are two oxygen independent steps, first a slow absorbance decrease (k = 4.3 s?1) and then an even slower increase (k = 0.55 s?1). The dihydroflavin peroxide is not expected to have absorption at 600 nm and is thus postulated to be in equilibrium with some flavin species which does absorb in the red. 相似文献
10.
Key components of swimming metabolism: standard metabolism (Rs), active metabolism (Ra) and absolute aerobic scope for activity (Ra–Rs) were determined for small age 0 year Atlantic cod Gadus morhua. Gadus morhua juveniles grew from 0·50 to 2·89 g wet body mass (MWB) over the experimental period of 100 days, and growth rates (G) ranged from 1·4 to 2·9% day?1, which decreased with increasing size. Metabolic rates were recorded by measuring changes in oxygen consumption over time at different activity levels using modified Brett‐type respirometers designed to accommodate the small size and short swimming endurance of small fishes. Power performance relationships were established between oxygen consumption and swimming speed measurements were repeated for individual fish as each fish grew. Mass‐specific standard metabolic rates () were calculated from the power performance relationships by extrapolating to zero swimming speed and decreased from 7·00 to 5·77 μmol O2 g?1 h?1, mass‐specific active metabolic rates () were calculated from extrapolation to maximum swimming speed (Umax) and decreased from 26·18 to 14·35 μmol O2 g?1 h?1 and mass‐specific absolute scope for activity was calculated as the difference between active and standard metabolism () and decreased from 26·18 to 14·35 μmol O2 g?1 h?1 as MWB increased. Small fish with low Rs had bigger aerobic scopes but, as expected, Rs was higher in smaller fish than larger fish. The measurements and results from this study are unique as Rs, Ra and absolute aerobic scopes have not been previously determined for small age 0 year G. morhua. 相似文献
11.
Sergio González-Moreno Juan Gómez-Barrera Hugo Perales Rafael Moreno-Sánchez 《Physiologia plantarum》1997,101(4):777-786
The effect of NaCl in the culture medium on growth, photosynthesis and cell content of chlorophyll, K+, Na+, Ca2+ and Mg2+ in Euglena gracilis was studied. O2 production, quantum yield of photosystem II (PSII), the non-photochemical quenching of chlorophyll fluorescence (qN) and the chlorophyll alb ratio all diminished by 0.2 M NaCl. Respiration and chlorophyll a and b increased, whereas the photochemical quenching (qp) of chlorophyll fluorescence was not affected by 0.2 M NaCl. Salt stress also induced an increase in cell volume and in K+ and Na+ concentrations, but decreased the concentrations of Ca2+ and Mg2+. Except for a protective effect on O2 production, additional Ca2+ in the culture medium did not attenuate the salt effect on the parameters measured. The addition of HCO3? restored the PSII quantum yield of O2 production in cells grown in high salt. Salt stress promoted a decrease in the apparent rate of quinone A (QA) reduction and an apparent obstruction of QB reduction, which were not prevented by excess HCO3?; the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) did not increase chlorophyll fluorescence in salt-grown cells. These results indicate that photosynthesis in Euglena grown under salt stress exhibits: (1) diminution of the HCO3? dependent water-splitting activity of PSII; (2) inhibition of the electron transfer at the quinone pool level; (3) probable increase in thylakoid stacking (as indicated by the effect on the chlorophyll alb ratio); and (4) dissipation of the H+ gradient across the thylakoid membranes (as indicated by the decrease of qN). 相似文献
12.
Wolf Bors Manfred Saran Christa Michel 《Biochimica et Biophysica Acta (BBA)/General Subjects》1979,582(3):537-542
Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (°OH), superoxide anions (O2?) or a combination of both oxygen radicals. The rate constant with °OH radicals was determined at 1.0·109 M?1·s?1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11–16), the rate constant with O2? of 1.0·107 M?1·s?1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with °OH and O2? of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of °OH radicals, leading to the same products with catechol compounds. 相似文献
13.
The kinetics of CNProto- and CNDeutero-hemin binding to apohemoglobin A2 was investigated in a stopped-flow device in 0.05 M potassium phosphate buffer, pH 7, at 10°C. The overall kinetic profile exhibited multiple phases: Phases I–IV corresponding with heme insertion (8.5?13 × 107 M?1 s?1), local structural rearrangement (0.21?0.23 s?1), global αδ structural event (0.071?0.098 s?1), and formation of the Fe–His bond (0.009?0.012 s?1), respectively. Kinetic differences observed between apohemoglobin A2 and apohemoglobin A (previously studied) prompted an analysis of the structures of β and δ chains through molecular modeling. This revealed a structural repositioning of the residues not only at, but also distant from the site of the amino acid substitutions, specifically those involved in the heme contact and subunit interface. A significant global change was observed in the structure of the exon-coded 3 region and provided additional evidence for the designation of this as the subunit assembly domain. 相似文献
14.
《Free radical research》2013,47(1-2):11-15
A kinetic model has been used to estimate the rate constant for the reaction of superoxide (O2/OOH) with the superoxide spin adduct of 5.5-dimethylpyrroline-N-oxide. DMPO/OOH. This rate constant is estimated to be 4.9 (± 2.2) × 106 M?1 s?1, pH 7.4 and 25°C. 相似文献
15.
《Free radical research》2013,47(1):173-177
Using the pulse radiolysis technique it was shown that copper(II) complexes of kinetin and 6-benzylaminopurine (6-BAP) catalyze O?2 dismutation very efficiently at physiological pH. The ‘turnover’ rate constants at pH 7 were determined to be (1.5 ± 0.3) × 109 and (2.2 ± 0.4) × 109 M?1 s?1for 6-BAP and kinetin, respectively. The system was studied at pH 3–10 in the case of 6-BAP, and the results show that this complex catalyzes also HO2 dismutation efficiently. 相似文献
16.
The reaction of Ru(XTPP)(DMF)2, where XTPP is the dianion of para substituted tetraphenylporphyrins and X is MeO, Me, H, Cl, Br, I, F, with O2 and CO were studied in DMF. The process was found to be first-order in metalloporphyrin, first-order in molecular oxygen and carbon monoxide, and second-order overall. Second-order rate constants for the CO reaction ranged from 0.170 to 0.665 M?1 s?1 at 25°C, those for the O2 reaction from 0.132 to 0.840 M?1 s?1 at 25°C. Similar activation parameters (ΔHCO± = 87 ± 1 kJ mol?1, ΔSCO± = 22 ± 4 JK?1 mol?1; ΔHO2± = 81 ± 1 kJ mol?1, and ΔSO2± = 11 ± 5 JK?1 mol?1) were found within each series. Reactivities of X substituted metalloporphyrins were found to follow different Hammett σ functions. The CO reactions correlated with σ? following normal behavior; the O2 reactions correlated with σ8° indicating O2 is π-bonded in the transition states. A dissociative mechanism is postulated for the process. 相似文献
17.
Abstract: A previous study of the metabolism of 6-[18F]-fluoro-l -3,4-dihydroxyphenylalanine (FDOPA) in rats pretreated with carbidopa contained information amenable to kinetic analysis. Using these data, tracer transfer coefficients and metabolic rate constants were estimated. After intravenous injection, FDOPA in circulation was O-methylated (kD0 = 0.055 min?1), and the metabolite (O-methyl-FDOPA) escaped from plasma with a rate constant (kM?1) of 0.01 min?1. The initial clearance of FDOPA to striatum (KD1) was 0.07 ml g?1 min?1, and the equilibrium distribution volume (VDe) was 0.67 ml g?1. The initial clearance of O-methyl-FDOPA to striatum (KM1) was 0.08 ml g?1 min?1, and the equilibrium distribution volume (VMe) was 0.75 ml g?1. The rate constant of FDOPA decarboxylation (kD3) was 0.17 min?1 in striatum. The elimination of 6-[18F]fluorodopamine (FDA) from striatum suggested an apparent rate constant for monoamine oxidase activity (k′7) of 0.055 min?1. 6-[18F]Fluorohomovanillic acid (FHVA) was formed from 6-[18F]fluoro-l -3,4-dihydroxyphenylacetic acid with a rate constant (k11) of 0.083 min?1, and FHVA was eliminated from striatum (k9) with a rate constant of 0.12 min?1. The steady-state concentration ratios of FDA and its metabolites were shown to be functions of these rate constants. 相似文献
18.
Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (LF), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (Ucrit) was 102·5 ± 13·7 cm s?1 or 4·6 ± 0·9 LF s?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (Umax,c) was 99·4 ± 14·4 cm s?1 or 4·5 ± 0·9 LF s?1. Oxygen consumption rate (M in mg O2 min?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O2 kg?1 h?1) as a function of relative speed (LF s?1) did not vary significantly with fish size. Mean standard metabolic rate (RS) was 170 ± 38 mg O2 kg?1 h?1, and the mean ratio of M at Umax,c to RS, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (Uopt), at which the gross cost of transport was a minimum of 2·14 J kg?1 m?1, was 3·8 LF s?1. In a subset of the fish studied (19·7–22·7 cm LF, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and LF. The mean propulsive wavelength was 86·7 ± 5·6 %LF or 73·7 ± 5·2 %LT. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm LF; 23·4, 25·3 and 26·4 cm LT), were 4·6 ± 0·1 and 17·1 ± 2·2 %LT, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis. 相似文献
19.
The rate of reaction between superoxide anion (O¯.2) and 1,2-dihydroxybenzene-3,5-disulfonic acid (tiron) was measured with pulse radiolysis-generated O¯.2. A kinetic spectrophotometric method utilizing competition betweenp-benzoquinoneand tiron for O¯.2 was employed. In this system, the known rate of reduction ofp-benzoquinonewas compared with the rate of oxidation of tiron to the semiquinone. From the concentration dependence of the rate of tiron oxidation, the absolute second order rate constant for the reaction was determined to be 5 · 108 M?·s?1. Ascorbat reduced O¯.2 to hydrogen peroxide with a rate constant of 108 M?1 · s?1 as determined by the same method. The tiron semiquinone may be used as an indicator free radical for the formation of superoxide anion in biological systems because of the rapid rate of oxidation of the catechol by O¯.2 compared to the rate of O¯.2 formation in most enzymatic systems.Tiron oxidation was used to follow the formation of superoxide anion in swollen chloroplasts. The chloroplasts photochemically reduced molecular oxygen which was further reduced to hydrogen peroxide by tiron. Tiron oxidation specifically required O¯.2 since O2 was consumed in the reaction and tiron did not reduce the P700 cation radical or other components of Photosystem I under anaerobic conditions. 相似文献
20.
Ronnie Nøhr Glud Michael Kühl Oliver Kohls Niels Birger Ramsing 《Journal of phycology》1999,35(2):270-279
By applying planar optodes and imaging techniques to a benthic photosynthetic mat, we demonstrated an extensive vertical and horizontal variation in O2 concentrations, O2 consumption, and O2 production. In light, the oxic zone could be divided into three horizons: 1) an upper zone dominated by diatoms that had a moderate net O2 production, 2) another zone dominated by Microcoleus-like cyanobacteria with a high net O2 production, and 3) a lower zone with disintegrating microalgae and cyanobacteria with a high O2 consumption rate. From the O2 images, the net O2 production/consumption was calculated at a spatial resolution of 130 μM. This allowed us to identify microsites with high rates of O2 turnover within the photic zone. Sites with high net O2 consumption (>1.5 nmol·cm?3·s?1) were typically situated next to sites with a relatively high net production (>2 nmol·cm?3·s?1), revealing a mosaic in which the highest O2 consumption sites were surrounded by the highest O2 production sites. This suggested a tight spatial coupling between production and consumption of O2 within the photic zone. Light stimulated the O2 consumption within the photic zone. At irradiances above 400 μmol photons·m?2·s?1, the stimulated O2 production was almost completely balanced by enhanced O2 consumption at microsites exhibiting net consumption of O2 even at maximum irradiance (578 μmol photons·m?2·s?1). Our observations strongly supported the idea that light-stimulated respiration was caused by stimulated heterotrophic activity fueled by organic carbon leakage from the phototrophs. Despite microsites with high net O2 consumption, anoxic microniches were not encountered in the investigated mat. Images of gross photosynthetic rates also revealed an extensive horizontal variation in gross rates, with microsites of low or no photosynthesis within the otherwise photic zone. Calculations based on the obtained images revealed that at maximum light (578 μmol photons·m?2·s?1), 90% of the O2 produced was consumed within the photic zone. The presented data demonstrate the great potential offered by planar optode for studies of benthic photosynthetic communities. 相似文献