To improve photodynamic activity of the parent hypocrellin B (HB), a tetra-brominated HB derivative (compound 1) was synthesized in high yield. Compared with HB, compound 1 has enhanced red absorption and high molar extinction coefficients. The photodynamic action of compound 1, especially the generation mechanism and efficiencies of active species (Sen·-, O·-2 and 1O2) were studied using electron paramagnetic resonance (EPR) and spectrophotometric methods. In the deoxygenated DMSO solution of compound 1, the semiquinone anion radical of compound 1 is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significantly promotes the reduction of compound 1. When oxygen is present, superoxide anion radical (O·-2) is formed via the electron transfer from Sens·- to the ground state molecular oxygen. The efficiencies of Sens·- and O·-2 generation by compound 1 are about three and two times as much as that of HB, respectively. Singlet oxygen (1O2) can be produced via the energy transfer from triplet compound 1 to ground state oxygen molecules. The quantum yield of singlet oxygen (1O2) is 0.54 in CHCl3 similar to that of HB. Furthermore, it was found that the accumulation of Sens·- would replace that of O·-2 or 1O2 with the depletion of oxygen in the sealed system. 相似文献
2-tert-butyl-(1), 2,6-dimethyl-(2), 2,5-dimethyl-(3), trimethyl-(4), and 2,3-dimethoxy-5-methyl-(5) substituted p-hydroquinones (QH2) were tested as a chainbreaking antioxidant during the oxidation of methyl linoleate (ML) in dodecyl sulfate micellar solution, pH 7.40, at 37°C. In the absence of superoxide dismutase (SOD), all the studied QH2 displayed very moderate if any antioxidant capability. When 5–25 U/ml SOD was added, QH2 showed a pronounced ability to inhibit ML oxidation. The stoichiometric factor of inhibition was found to be about one for all the tested QH2 in the presence of SOD. The reactivities of QH2 to the ML peroxy radical increase in the order QH25 < QH23 < QH21≈QH22 < QH24; reactivity of QH24 exceds that reported for the majority of phenolic antioxidants. The features of QH2 as an antioxidant in aqueous environment is likely associated with the reactivity of semiquinone (O·-) formed due to attack of the peroxy radical to QH2. O·- reacts readily with molecular oxygen with formation of superoxide (O·-2); in turn, O·-2 attacks both to QH2 and ML (likely, as HO·2) that results in fast depleting QH2 and chain propagation, respectively. The addition of SOD results in purging a reaction mixture from O·-2 and, as a corollary, in depressing undesirable reactions with the participation of O·-2. Under these conditions, QH2 displays the theoretically highest inhibitory activity which is determined solely by the reactivity of QH2 to the peroxy radical. 相似文献
Oxygen radical scavengers have been shown to prevent the development of ischemic preconditioning, suggesting that reactive oxygen species (ROS) might be involved in this phenomenon. In the present study, we have investigated whether direct exposure to ROS produced by photoactivated Rose Bengal (RB) could mimic the protective effects of ischemic preconditioning.Methods In vitro generation of ROS from photoactivated RB in a physiological buffer was first characterised by ESR spectroscopy in the presence of 2,2,6,6-tetramethyl-1-piperidone (oxoTEMP) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In a second part of the study, isolated rat hearts were exposed for 2.5 min to photoactivated RB. After 5 min washout, hearts underwent 30 min no-flow normothermic ischemia followed by 30 min of reperfusion.Results and Conclusions The production of singlet oxygen (1O2) by photoactivated RB in the perfusion medium was evidenced by the ESR detection of the nitroxyl radical oxoTEMPO. Histidine completely inhibited oxoTEMPO formation. In addition, the use of DMPO has indicated that (i) superoxide anions (O·-2) are produced directly and (ii) hydroxyl radicals (HO·) are formed indirectly from the successive O·-2 dismutation and the Fenton reaction. In the perfusion experiments, myocardial post-ischemic recovery was dramatically impaired in hearts previously exposed to the ROS produced by RB photoactivation (1O2, O·-2, H2O2 and HO·) as well as when 1O2 was removed by histidine (50 mM) addition. However, functional recovery was significantly improved when hearts were exposed to photoactivated RB in presence of superoxide dismutase (105 IU/L) and catalase (106 IU/L).Further studies are now required to determine whether the cardioprotective effects of Rose Bengal in presence of O·-2 and H2O2 scavengers are due to singlet oxygen or to other species produced by Rose Bengal degradation. 相似文献
The interaction of superoxide radical anion (O2??) with active dicarbonyls (methylglyoxal, glyoxal, and malonic dialdehyde) was studied. It was demonstrated that glyoxal and methylglyoxal inhibited superoxide-dependent accumulation of formazan; however, malonic dialdehyde stimulated this process. The formation of O2?? in these experiments occurred during the decomposition of the SOTS-1 azo initiator. On the other hand, all of the studied dicarbonyls in this system of O2?? generation competed for superoxide with the TIR ON spin trap. These compounds also inhibited luminal-dependent chemiluminescence during the AIBN azo initiator-induced peroxidation of liposomes from the egg phosphatidylcholine. A mechanism for the antiradical and antioxidant effects of the studied dicarbonyls, assuming the production of free radical intermediates in their reactions with O2?? or its protonated form, is proposed. 相似文献
To define the molecular mechanism(s) of carvedilol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process.Carvedilol inhibits the peroxidation of sonicated phosphatidylcholine liposomes triggered by FeCl2 addition whereas atenolol, pindolol and labetalol are ineffective. The inhibition proved not to be ascribable (a) to an effect on Fe2+ autoxidation and thus on the generation of oxygen derived radical initiators; (b) to the scavenging of the inorganic initiators O·-2 and ·OH; (c) to an effect on the reductive cleavage of organic hydroperoxides by FeCl2; (d) to the scavenging of organic initiators. The observations that (a) carvedilol effectiveness is inversely proportional to the concentration of FeCl2 and lipid hydroperoxides in the assay; (b) the drug prevents the onset of lipid peroxidation stimulated by FeCl3 addition and; (c) it can form a complex with Fe3+, suggest a molecular mechanism for carvedilol action. It may inhibit lipid peroxidation by binding the Fe3+ generated during the oxidation of Fe2+ by lipid hydroperoxides in the substrate. The lag time that carvedilol introduces in the peroxidative process would correspond to the time taken for carvedilol to be titrated by Fe3+; when the drug is consumed the Fe3+ accumulates to reach the critical parameter that stimulates peroxidation. According to this molecular mechanism the antioxidant potency of carvedilol can be ascribed to its ability to bind a species, Fe3+, that is a catalyst of the process and to its lipophilic nature that concentrates it in the membranes where Fe3+ is generated by a site specific mechanism. 相似文献
Nitric oxide, a gaseous free radical, is poorly reactive with most biomolecules but highly reactive with other free radicals. Its ability to scavenge peroxyl and other damaging radicals may make it an important antioxidant in vivo, particular in the cardiovascular system, although this ability has been somewhat eclipsed in the literature by a focus on the toxicity of peroxynitrite, generated by reaction of O·-2 with NO· (or of NO- with O2). On balance, experimental and theoretical data support the view that ONOO- can lead to hydroxyl radical (OH·) generation at pH 7.4, but it seems unlikely that OH· contributes much to the cytotoxicity of ONOO-. The cytotoxicity of ONOO- may have been over-emphasized: its formation and rapid reaction with antioxidants may provide a mechanism of using NO· to dispose of excess O·-2, or even of using O·-2 to dispose of excess NO·, in order to maintain the correct balance between these radicals in vivo. Injection or instillation of “bolus” ONOO- into animals has produced tissue injury, however, although more experiments generating ONOO- at steady rates in vivo are required. The presence of 3-nitrotyrosine in tissues is still frequently taken as evidence of ONOO- generation in vivo, but abundant evidence now exists to support the view that it is a biomarker of several “reactive nitrogen species”. Another under-addressed problem is the reliability of assays used to detect and measure 3-nitrotyrosine in tissues and body fluids: immunostaining results vary between laboratories and simple HPLC methods are susceptible to artefacts. Exposure of biological material to low pH (e.g. during acidic hydrolysis to liberate nitrotyrosine from proteins) or to H2O2 might cause artefactual generation of nitrotyrosine from NO-2 in the samples. This may be the origin of some of the very large values for tissue nitrotyrosine levels quoted in the literature. Nitrous acid causes not only tyrosine nitration but also DNA base deamination at low pH: these events are relevant to the human stomach since saliva and many foods are rich in nitrite. Several plant phenolics inhibit nitration and deamination in vitro, an effect that could conceivably contribute to their protective effects against gastric cancer development. 相似文献
The kinetics of O·-2 reaction with semi-oxidized tryptophan radicals in lysozyme, Trp·(Lyz) have been investigated at various pHs and conformational states by pulse radiolysis. The Trp·(Lyz) radicals were formed by Br·-2 oxidation of the 3–4 exposed Trp residues in the protein. At pH lower than 6.2, the apparent bimolecular rate is about 2 × 108M-1s-1; but drops to 8 × 107M-1s-1 or less above pH 6.3 and in CTAC micelles. Similarly, the apparent bimolecular rate constant for the intermolecular Trp·(Lyz) + Trp·(Lyz) recombination reaction is about (4-7 × 106M-1s-1) at/or below pH 6.2 then drops to 1.3-1.6 × 106M-1s-1 at higher pH or in micelles. This behavior suggests important conformational and/or microenvironmental rearrangement with pH, leading to less accessible semioxidized Trp· residues upon Br·-2 reaction. The kinetics of Trp·(Lyz) with ascorbate, a reducing species rather larger than O·-2 have been measured for comparison. The well-established long range intramolecular electron transfer from Tyr residues to Trp radicals-leading to the repair of the semi-oxidized Trp·(Lyz) and formation of the tyrosyl phenoxyl radical is inhibited by the Trp·(Lyz)+O·-2 reaction, as is most of the Trp·(Lyz)+Trp·(Lyz) reaction. However, the kinetic behavior of Trp·(Lyz) suggests that not all oxidized Trp residues are involved in the intermolecular recombination or reaction with O·-2. As the kinetics are found to be quite pH sensitive, this study demonstrates the effect of the protein conformation on O·-2 reactivity. To our knowledge, this is the first report on the kinetics of a protein-O·-2 reaction not involving the detection of change in the redox state of a prosthetic group to probe the reactivity of the superoxide anion. 相似文献
Thioctic acid (TA) and its reduced form dihydrolipoic acid (DHLA) have recently gained somc recognition as useful biological antioxidants. In particular, the ability of DHLA to inhibit lipid peroxidation has been reported. In the present study, the effects of TA and DHLA on reactive oxygen species (ROS) generated in the aqueous phase have been investigated. Xanthine plus xanthine oxidase-generated superoxide radicals (O2), detected by electron spin resonance spectroscopy (ESR) using DMPO as a spin trap. were eliminated by DHLA but not by TA. The sulhydryl content of DHLA, measured using Ellman's reagent decreased subsequent to the incubation with xanthine plus xanthine oxidase confirming the interaction between DHLA and O2-. An increase of hydrogen peroxide concentration accompanied the reaction between DHLA and O2x, suggesting the reduction of O2- by DHLA. Competition of O2- with epinephrine allowed us to estimate a second order kinetic constant of the reaction between O2- and DHLA, which was found to be a 3.3 × 105 M-1 s-1. On the other hand, the DMPO signal of hydroxyl radicals (HO ·) generated by Fenton's reagent were eliminated by both TA and DHLA. Inhibition of the Fenton reaction by TA was confirmed by a chemiluminescence measurement using luminol as a probe for HO ·. There was no electron transfer from Fe2+ to TA or from DHLA to Fe3 + detected by measuring the Fe2+ -phenanthroline complex. DHLA did not potentiate the DMPO signal of HO · indicating no prooxidant activity of DHLA. These results suggest that both TA and DHLA possess antioxidant properties. In particular. DHLA is very effective as shown by its dual capability by eliminating both O2-; and HO ·. 相似文献
Sphaerophysa kotschyana is a Turkish endemic and endangered plant that grows near Salt Lake, in Konya, Turkey. However, little is known about the ability of this plant to generate/remove reactive oxygen species (ROS) or its adaptive biochemical responses to saline environments. After exposure of S. kotschyana to 0, 150, and 300 mM NaCl for 7 and 14 days, we investigated (1) the activities and isozyme compositions of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), and glutathione reductase (GR); (2) the oxidative stress parameters NADPH oxidase (NOX) activity, lipid peroxidation (MDA), total ascorbate (tAsA) content, and total glutathione content (tGlut); and (3) ROS levels for superoxide anion radical (O2·?), hydrogen peroxide (H2O2), hydroxyl radicals (OH·), and histochemical staining of O2·? and H2O2. H2O2 content increased after 14 days of salt stress, which was consistent with the results from histochemical staining and NOX activity measurements. In contrast, oxidative stress induced by 150 mM NaCl was more efficiently prevented, as indicated by low malondialdehyde (MDA) levels and especially at 7 days, by increased levels of SOD, POX, APX, and GR. However, at 300 mM NaCl, decreased levels of protective enzymes such as SOD, CAT, POX, and GR, particularly with long-term stress (14 days), resulted in limited ROS scavenging activity and increased MDA levels. Moreover, at 300 mM NaCl, the high H2O2 content caused oxidative damage rather than inducing protective responses against H2O2. These results suggest that S. kotschyana is potentially tolerant to salt-induced damage only at low salt concentrations. 相似文献
Many of the cytopathic effects of nitric oxide (NO·) are mediated by peroxynitrite (PN), a product of the reaction between NO· and superoxide radical (O·?2). In the present study, we investigated the role of PN, O·?2 and hydroxyl radical (OH·) as mediators of epithelial hyperpermeability induced by the NO· donor, S-nitroso-N-acetylpenicillamine (SNAP), and the PN generator, 3-morpholinosydnonimine (SIN-1). Caco-2BBe enterocytic monolayers were grown on permeable supports in bicameral chambers. Epithelial permeability, measured as the apical-to-basolateral flux of fluorescein disulfonic acid, increased after 24 h of incubation with 5.0 mM SNAP or SIN-1. Addition of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, an NO· scavenger, or Tiron, an O·?2 scavenger, reduced the increase in permeability induced by both donor compounds. The SNAP-induced increase in permeability was prevented by allopurinol, an inhibitor of xanthine oxidase (a source of endogenous O·?2). Diethyldithiocarbamate, a superoxide dismutase inhibitor, and pyrogallol, an O·?2 generator, potentiated the increase in permeability induced by SNAP. Addition of the PN scavengers deferoxamine, urate, or glutathione, or the OH· scavenger mannitol, attenuated the increase in permeability induced by both SNAP and SIN-1. Both donor compounds decreased intracellular levels of glutathione and protein-bound sulfhydryl groups, suggesting the generation of a potent oxidant. These results support a role for PN, and possibly OH·, in the pathogenesis of NO· donor-induced intestinal epithelial hyperpermeability. 相似文献
To investigate whether paraquat (PQ) is involved in regulation of antioxidant enzymes and lipid peroxidation under short-term
salt stress, and to elucidate the physiological mechanism of salt stress mitigated by PQ, a cucumber cultivar (cv. Chunguang
no. 2) was exposed to 100 mM NaCl for 48 h after pre-treatment with 10 μM PQ for 1 h. When compared to the control, salt stress
increased the levels of malonaldehyde (MDA), superoxide radical (O2·−) and hydrogen peroxide (H2O2) and the activities of antioxidant enzymes, such as superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11)
and glutathione reductase (EC 1.6.4.2) in the cucumber leaves. Under salt conditions, PQ pre-treatment prevented oxidative
stress as observed by the decreases in MDA, H2O2 and O2·− that correlated with the increase in antioxidant defenses. We propose that, at low concentrations, the PQ pre-treatment can
reduce the salt-induced oxidative damage by increasing the antioxidative mechanisms in cucumber plants. 相似文献
The α-aminoketone 1,4-diamino-2-butanone (DAB), a putrescine analogue, is highly toxic to various microorganisms, including Trypanosoma cruzi. However, little is known about the molecular mechanisms underlying DAB's cytotoxic properties. We report here that DAB (pKa 7.5 and 9.5) undergoes aerobic oxidation in phosphate buffer, pH 7.4, at 37 °C, catalyzed by Fe(II) and Cu(II) ions yielding NH4+ ion, H2O2, and 4-amino-2-oxobutanal (oxoDAB). OxoDAB, like methylglyoxal and other α-oxoaldehydes, is expected to cause protein aggregation and nucleobase lesions. Propagation of DAB oxidation by superoxide radical was confirmed by the inhibitory effect of added SOD (50 U ml? 1) and stimulatory effect of xanthine/xanthine oxidase, a source of superoxide radical. EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) revealed an adduct attributable to DMPO–HO?, and those with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 3,5-dibromo-4-nitrosobenzenesulfonic acid, a six-line adduct assignable to a DAB? resonant enoyl radical adduct. Added horse spleen ferritin (HoSF) and bovine apo-transferrin underwent oxidative changes in tryptophan residues in the presence of 1.0–10 mM DAB. Iron release from HoSF was observed as well. Assays performed with fluorescein-encapsulated liposomes of cardiolipin and phosphatidylcholine (20:80) incubated with DAB resulted in extensive lipid peroxidation and consequent vesicle permeabilization. DAB (0–10 mM) administration to cultured LLC-MK2 epithelial cells caused a decline in cell viability, which was inhibited by preaddition of either catalase (4.5 μM) or aminoguanidine (25 mM). Our findings support the hypothesis that DAB toxicity to several pathogenic microorganisms previously described may involve not only reported inhibition of polyamine metabolism but also DAB pro-oxidant activity. 相似文献
In this study, electron paramagnetic resonance spin-trapping spectroscopy was used to study the light-induced production of superoxide anion (O2?-) and carbon-centered (R?) radicals by Photosystem II (PSII). It is evidenced here that exposure of PSII membranes to high light (2,000 μmol photons m?2 s?1) or heat (47 °C) treatments prior to the illumination suppressed O2?- production, while R? was formed. Formation of R? in the both high light- and heat-treated PSII membranes was enhanced by DCMU. Removal of molecular oxygen by glucose/glucose oxidase/catalase system and O2?- scavenging by exogenous superoxide dismutase completely suppressed carbon-centered radical formation. It is proposed here that the oxidation of polyunsaturated fatty acids and amino acids by O2?- on the electron acceptor side of PSII results in the formation of R?, known to initiate a cascade reaction leading to the lipid peroxidation and protein degradation, respectively. 相似文献
A gray and low viscosity extracellular polysaccharide (EPS) composed of N-acetylglucosamine, xylose, and mannose was isolated
from culture medium of Bacillus sp. strain LBP32 by ethanol precipitation followed by dialysis and freeze-drying. The crude biopolymer showed an apparent
molecular weight (Mw) of ∼ 9.62 × 104. Chemical and spectroscopic studies revealed that the bacterial biopolymer was composed of a β-1,4-linked backbone carrying
a low content of β-1,3-linked backbone. In addition, the EPS demonstrated a high antioxidant activity in a concentration dependent
manner. The 50% inhibition concentration (IC50) for quenching hydroxyl radical (·OH) and superoxide radical (·O2−) were 0.042 and 0.165 mg/mL, respectively. Furthermore, the EPS demonstrated a strong protective effect against lipid peroxidation
and radiation such as UV radiation and ion beam irradiation. These results indicate that the protective effects of the EPS
were most likely due to its free radical scavenging ability. 相似文献
Over-expression of the gene, mshA, coding for mycothiol glycosyl transferase improved the robustness of Corynebacterium glutamicum to various stresses. Intracellular mycothiol (MSH) content was increased by 114 % in WT(pXMJ19-mshA) compared to WT(pXMJ19). Survival rates increased by 44, 39, 90, 77, 131, 87, 52, 47, 57, 85 and 33 % as compared to WT(pXMJ19) under stress by H2O2 (40 mM), methylglyoxal (5.8 mM), erythromycin (0.08 mg ml?1), streptomycin (0.005 mg ml?1), Cd2+ (0.01 mM), Mn2+ (2 mM), formic acid (0.05 %), acetic acid (0.15 %), levulinic acid (0.25 %), furfural (7.2 mM), and ethanol (10 % v/v), respectively. Increased MSH content also decreased the concentration of reactive oxygen species in the presence of the above stresses. Our results may open a new avenue for enhancing robustness of industrial bacteria for production of commodity chemicals. 相似文献
The reaction of the superoxide radical anion (O-·2), with the semi-oxidized tryptophan neutral radical (Trp·) generated from tryptophan (Trp) by pulse radiolysis has been observed in a variety of functionalized Trp derivatives including peptides. It is found that the reaction proceeds 4–5 times faster in positively charged peptides, such as Lys-Trp-Lys, Lys-Gly-Trp-Lys and Lys-Gly-Trp-Lys-O-tert-butyl, than in solutions of the negatively charged N-acetyl tryptophan (NAT). However, the reactivity of O-·2 with the Trp· radical is totally inhibited upon binding of these peptides to micelles of negatively charged SDS and is reduced upon binding to native DNA. By contrast, no change in reactivity is observed in a medium containing CTAB, where the peptides cannot bind to the positively charged micelles. On the other hand, the reactivity of the Trp· radical formed from NAT with O-·2 is reduced to half that of the free Trp· in buffer but is markedly increased in CTAB micelles. The models studied here incorporate elements of the complex environment in which Trp· and O-·2 may be concomitantly formed in biological system and demonstrate the magnitude of the influence such elements may have on the kinetics of reactions involving these two species. 相似文献
It was found that glucose in the range of concentrations 12.5–100 mM stimulated Cu2+–mediated free radical peroxidation of low-density lipoproteins (LDL) from human blood plasma. Considering the kinetic parameters of LDL peroxidation we proposed that intensification of this process may be caused by formation of free radical intermediates of glucose auto-oxidation. Addition of SOD to the medium inhibited LDL oxidation, indicating the formation of superoxide anion-radicals under autoxidation of glucose. Similarly, SOD inhibited free radical peroxidation of liposomes from egg lecithin in the presence of glucose that confirms the generation of superoxide radicals under co-oxidation of unsaturated lipids and glucose. Normalization of glucose level in the blood of patients with type 2 diabetes mellitus during therapy was accompanied by a significant decrease in LDL oxidation in vivo (the decrease in primary and secondary lipoperoxidation products). The formation of superoxide anion-radicals was observed during interaction of aminoacid l-lysine with a product of glucose oxidative metabolism–methylglyoxal, but not with a product of lipoperoxidation malonyldialdehyde. In accordance with the foregoing the administration of sugar-lowering drug metformin, which binds and utilizes methylglyoxal, caused a stronger inhibition of LDL peroxidation in the blood of patients with diabetes mellitus, probably due to decrease in methylglyoxal-dependent generation of superoxide anion-radicals. Based on the results we set out the hypothesis about autocatalytic mechanism of free radical reactions involving natural dicarbonyls and suppose the common molecular mechanism of vascular wall injury in atherosclerosis and diabetes. 相似文献
Polyamines (PAs) produce H2O2 and nitric oxide (NO) during their normal catabolism and modulate plant growth and development. To explore the biochemical basis of PAs-induced growth inhibition in Triticum aestivum L seedlings, we examined the role of O2·-, H2O2 or NO in shoot and root development. Although all PA treatments resulted in a variable reduction of root and shoot elongation, spermine (Spm) caused the greater inhibition in a similar way to that observed with the NO donor, sodium nitroprusside (SNP). In both cases, O2·- production was completely blocked whereas H2O2 formation was high in the root apex under SNP or Spm treatments. Catalase recovered root and shoot growth in SNP but not in Spm-treated plants, revealing the involvement of H2O2 in SNP-root length reduction. The addition of the NO scavenger, cPTIO, restored root length in SNP- or Spm-treated plants, respectively, and partially recovered O2·- levels, compared to the plants exposed to PAs or SNP without cPTIO. A strong correlation was observed between root growth restoration and O2·- accumulation after treating roots with SNP + aminoguanidine, a diamine oxidase inhibitor, and with SNP + 1,8-diaminoctane, a polyamine oxidase inhibitor, confirming the essential role of O2·- formation for root growth and the importance of the origin and level of H2O2. The differential modulation of wheat growth by PAs through reactive oxygen species or NO is discussed.
1. Ionophore A23187 induces uncoupling of potassium ferricyanide-dependent O2 evolution by envelope-free chloroplasts and oxaloacetate-dependent O2 evolution by intact chloroplasts. The half maximal concentration () for stimulation of oxygen evolution in both cases is approximately 4 μM · 100 μg chlorophyll · ml?1.2. Ionophore A23187 also induces inhibition of CO2 and 3-phosphoglycerate-dependent O2 evolution by intact chloroplasts in the presence of 3 mM MgCl2. The half maximal concentrations () for inhibition of O2 evolution are 3 μM and 5 μM respectively · 100 μg?1 chlorophyll · ml?1.3. A very high concentration of ionophore A23187 (10 μM · 20 μg?1 chlorophyll · ml?1) plus 0.1 mM EDTA lowers the fluorescence yield of intact chloroplasts suspended in a cation-free medium in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicating loss of divalent cation from the diffuse double layers of the thylakoid membranes.4. These results are discussed in relation to ionophore A23187-induced divalent cation/proton exchange at both the thylakoid and the envelope membranes of intact chloroplasts. 相似文献