Sensitivity of ATPase-ADPase activities from synaptic plasma membranes of rat forebrain to lipid peroxidation in vitro and the protective effect of vitamin E

The in vitro effects of membrane lipid peroxidation on ATPase-ADPase activities in synaptic plasma membranes from rat forebrain were investigated. Treatment of synaptic plasma membranes with an oxidant generating system (H₂O₂/Fe²⁺/ascorbate) resulted in lipid peroxidation and inhibition of the enzyme activity. Besides, trolox as a water soluble vitamin E analogue totally prevented lipid peroxidation and the inhibition of enzyme activity. These results demonstrate the susceptibility of ATPase-ADPase activities of synaptic plasma membranes to free radicals and suggest that the protective effect against lipid peroxidation by trolox prevents the inhibition of enzyme activity. Thus, inhibition of ATPase-ADPase activities of synaptic plasma membranes in cerebral oxidative stress probably is related to lipid peroxidation in the brain.     

Hemoglobin degradation lipid peroxidation,and inhibition of na+/k+-atpase in rat erythrocytes exposed to acrylonitrile

The effect of acrylonitrile (VCN) on erythrocyte lipid metabolism was investigated in vitro in metabolically active red cells from male Sprague-Dawley rats containing three types of hemoglobins: oxyhemoglobin, methemoglobin, and carbon monoxyhemoglobin. VCN at the concentration of 10 mM rapidly depleted erythrocyte glutathione (GSH) (75% of control) and induced lipid peroxidation (274% of control). Degradation of oxy- and methemoglobin was directly proportional to the extent of lipid peroxidation (r = 0.89). Addition of glucose to the incubation medium decreased hemoglobin degradation while it slightly increased VCN-induced lipid peroxidation. The highest amount of lipid peroxidation occurred in erythrocytes containing carbon monoxyhemoglobin and glucose. In the isolated red cell membranes incubated with 10 mM VCN, the lipid peroxidation was 400% of controls. VCN (25 mM) noncompetitively inhibited erythrocyte membrane Na⁺/K⁺-ATPase activity and the degree of inhibition was inversely proportional to the reaction temperature (r = ?0.88). These findings indicate that the VCN induced hemoglobin degradation and lipid peroxidation are two extremes of a spectrum of oxidative damage in red cells leading to a change in physical state of membrane structure causing inhibition of adenosine triphosphatase (ATPase) activity.     

The effects of assay temperature upon the pH optima of enzymes from poikilotherms: A test of the imidazole alphastat hypothesis

Summary A study of the thermal responses of Na-ATPase and NaK-ATPase activities in microsomes prepared from gill tissue of rainbow trout (Salmo gairdneri) revealed further evidence that the two activities are distinct from one another. Arrhenius plots of the NaK-ATPase from sea water-adapted fish and the Na-ATPase from fresh water-adapted fish were linear (Fig. 4) with estimated activation energies of 19.5 and 7.7 kcal/mole, respectively. The Na-ATPase and NaK-ATPase both showed optimum activity at 45°C (Figs. 2 and 3). The Mg-ATPase from fresh water fish showed a distinct temperature optimum at 24°C (Fig. 1) while Mg-ATPase activity from sea water fish was optimum at temperatures of about 15–24 °C (Fig. 3). The Na⁺ dependence of the Na-ATPase and the NaK-ATPase was examined at an assay temperature of 37 °C (Fig. 5) and the results compared with those obtained at 13 °C. No apparent differences were noted for the Na-ATPase, but with the NaK-ATPase both theK _0.5 for Na⁺ and optimum Na⁺ concentration increased at the higher assay temperature. Finally, evidence is presented showing the Na-ATPase to be distinct from Mg-ATPase activity in fresh water trout gill microsomes.Abbreviation HEPES N-2-hydroxyethylpiperazine-N-2-ethane-sulfonic acid     

Osmotic stress and viscous retardation of the Na,K-ATPase ion pump

The transport function of the Na pump (Na,K-ATPase) in cellular ion homeostasis involves both nucleotide binding reactions in the cytoplasm and alternating aqueous exposure of inward- and outward-facing ion binding sites. An osmotically active, nonpenetrating polymer (poly(ethyleneglycol); PEG) and a modifier of the aqueous viscosity (glycerol) were used to probe the overall and partial enzymatic reactions of membranous Na,K-ATPase from shark salt glands. Both inhibit the steady-state Na,K-ATPase as well as Na-ATPase activity, whereas the K⁺-dependent phosphatase activity is little affected by up to 50% of either. Both Na,K-ATPase and Na-ATPase activities are inversely proportional to the viscosity of glycerol solutions in which the membranes are suspended, in accordance with Kramers’ theory for strong coupling of fluctuations at the active site to solvent mobility in the aqueous environment. PEG decreases the affinity for Tl⁺ (a congener for K⁺), whereas glycerol increases that for the nucleotides ATP and ADP in the presence of NaCl but has little effect on the affinity for Tl⁺. From the dependence on osmotic stress induced by PEG, the aqueous activation volume for the Na,K-ATPase reaction is estimated to be ∼5-6 nm³ (i.e., ∼180 water molecules), approximately half this for Na-ATPase, and essentially zero for p-nitrophenol phosphatase. The change in aqueous hydrated volume associated with the binding of Tl⁺ is in the region of 9 nm³. Analysis of 15 crystal structures of the homologous Ca-ATPase reveals an increase in PEG-inaccessible water space of ∼22 nm³ between the E₁-nucleotide bound forms and the E₂-thapsigargin forms, showing that the experimental activation volumes for Na,K-ATPase are of a magnitude comparable to the overall change in hydration between the major E₁ and E₂ conformations of the Ca-ATPase.     

Evidence for the accumulation of peroxidized lipids in membranes of senescing cotyledons

Fluorescent products of lipid peroxidation accumulate with age in microsomal membranes from senescing cotyledons of Phaseolus vulgaris. The temporal pattern of accumulation is closely correlated with a rise in the lipid phase transition temperature reflecting the formation of gel phase lipid. Increased levels of fluorescent peroxidation products are also detectable in total lipid extracts of senescent cotyledons. Lipoxygenase activity increases with advancing age by about 3-fold on a fresh weight basis and 4-fold on a dry weight basis indicating that the tissue acquires elevated levels of lipid hydroperoxides. As well, levels of glutathione and superoxide dismutase activity decline on a dry weight basis as the cotyledons age, rendering the tissue more susceptible to oxidative damage. Catalase activity rises initially and then declines during senescence, but peroxidase activity rises steeply. Thus, apart from this increase in peroxidase, which would scavenge H₂O₂ only if appropriate cosubstrates were available, the defense mechanisms for coping with activated oxygen species (O₂⁻, H₂O₂, OH) are less effective in the older tissue. The observations support the contention that formation of gel phase lipid in senescing membranes is attributable to lipid peroxidation and suggest that the reactions of lipid peroxidation are utilized by the cotyledons to mediate deteriorative changes accompanying the mobilization and transport of metabolites from the storage tissue to the developing embryo.     

Selenium as an anti-oxidant and pro-oxidant in ryegrass

Selenium is an essential element for antioxidation reactions in human and animals. In order to study its biological role in higher plants, ryegrass (Lolium perenne) was cultivated in a soil without Se or amended with increasing dosages of H₂SeO₄ (0.1, 1.0, 10.0 and 30.0 mg Se kg⁻¹). Ryegrass was harvested twice and the yields were analyzed for antioxidative systems and growth parameters. Selenium exerted dual effects: At low concentrations it acted as an antioxidant, inhibiting lipid peroxidation, whereas at higher concentrations, it was a pro-oxidant, enhancing the accumulation of lipid peroxidation products. The antioxidative effect was associated with an increase in glutathione peroxidase (GSH-Px) activity, but not with superoxide dismutase (SOD) and αα-tocopherol, which was the only tocopherol detected. In the second yield, the diminished lipid peroxidation due to a proper Se addition coincided with promoted plant growth. The oxidative stress found at the Se addition level ≥ 10 mg kg⁻¹ resulted in drastic yield losses. This result indicates that the toxicity of Se can be attributed, in addition to metabolic disturbances, to its pro-oxidative effects. Neither the growth-promoting nor the toxic effect of Se could be explained by the changes in the total chlorophyll concentration. This revised version was published online in June 2006 with corrections to the Cover Date.     

Free Radical Scavenging and Antioxidative Properties of ‘Silibin’ Complexes on Microsomal Lipid Peroxidation

The antioxidant properties of silibin complexes, the water-soluble form silibin dihemisuccinate (SDH), and the lipid-soluble form, silibin phosphatidylcholine complex known as IdB 1016, were evaluated by studying their abilities to react with the superoxide radical anion (O₂^.−), and the hydroxyl radical (OH^.). In addition, their effect on pulmonary and hepatic microsomal lipid peroxidation had been investigated. Superoxide radicals were generated by the PMS-NADH system and measured by their ability to reduce NBT. IC₅₀ concentrations for the inhibition of the NBT reduction by SDH and IdB 1016 were found to be 25 μM and 316 μM respectively. Both silibin complexes had an inhibitory effect on xanthine oxidase activity. SDH reacted rapidly with OH^. radicals at approximately diffusion controlled rate and the rate constant was found to be (K=8·2×10⁹ M ⁻¹ s⁻¹); it appeared to chelate Fe²⁺ in solution. In hepatic microsomes, when lipid peroxidation was induced by Fe²⁺, SDH inhibited by 39·5 per cent and IdB 1016 by 19·5 per cent, whereas when lipid peroxidation was induced by CuOOH, IdB 1016 exerted a better protective effect than SDH (29·4 per cent and 19·4 per cent inhibition, respectively). In both microsomal systems lipid peroxidation proceeded through a thiol depletion mechanism which could be restored in the presence of silibin complexes. Low levels of lipid peroxidation in pulmonary microsomes point out the differences between in-vitro lipid peroxidation occurring in microsomes of different tissues. The results support the free radical scavenger and antioxidative properties of silibin when it is complexed with a suitable molecule to increase its bioavailabilty. © 1997 John Wiley & Sons, Ltd.     

Effect of soil salinity, soil drought, and their combined action on the biochemical characteristics of cotton roots

Stress caused by soil salinity and soil drought limits cotton productivity in China. To determine the tolerance levels of cotton, we assessed the effects of soil salinity and soil drought on the biochemical characteristics of the roots of two cotton cultivars (CCRI-44, salt-tolerant; Sumian 12, salt-sensitive). Specifically, we analyzed root biomass, fatty acid composition, antioxidative enzyme activity, lipid peroxidation, H⁺-ATPase and Ca²⁺-ATPase activities. The cotton root biomass of the two cultivars declined significantly under conditions of soil salinity, soil drought, and the two stressors combined. The antioxidant enzyme activity of the roots also decreased markedly, which caused lipid peroxidation to increase, and changed the composition of the fatty acid membrane. H⁺-ATPase, Ca²⁺-ATPase and antioxidant enzyme activity decreased more under the two stressors combined. However, H₂O₂ content and O₂ ^? generation increased under the two stressors combined, compared to each stressor separately. Overall, the combination of soil salinity and drought has a greater inhibitory effect and more harmful impact on root growth than each stressor separately. The higher tolerance of CCRI-44 to soil salinity and drought stress than Sumian 12 might be explained by differences in cotton root antioxidative enzyme activity. The lipid peroxidation levels of cotton roots might represent an important biochemical trait for stress tolerance.     

Changes in lipid peroxidation, the redox system and ATPase activities in plasma membranes of rice seedling roots caused by lanthanum chloride

Highly purified plasma membranes were isolated by aqueous two-phase partitioning from rice (Oryza sativa) seedling roots. The effects of lanthanum chloride (LaCl₃) on the activities of lipid peroxidation, the redox system and H⁺-ATPase, Ca²⁺-ATPase of plasma membranes were studied. The lipid peroxidation of plasma membranes could be depressed by certain low concentrations of LaCl₃ and enhanced by high concentrations of LaCl₃, while the lipid peroxidation was also dependent on the plasma membrane protein and incubation time. The relative activity of O₂ uptake of plasma membranes was inhibited by all tested LaCl₃ concentrations. In contrast, the reduction rate of Fe(CN)₆ ^3– by plasma membranes was stimulated below 40 M of LaCl₃, but was reduced above 60 M of LaCl₃. The relative activities of both H⁺-ATPase and Ca²⁺-ATPase increased constantly from control to LaCl₃ of concentration 60 M where the activities of both enzymes were the maximum, but decreased remarkably at 80 M LaCl₃ concentrations various LaCl₃ were added to culture solutions. In the other measurement case in which various LaCl₃ concentrations were added directly to reaction medium and the plasma membrane vesicles only came from the control cultured rice seedling roots, the response of H⁺-ATPase activity to La³⁺ was similar to the response in culture solution. However, the La³⁺ concentration was only 20 M when the activity of H⁺-ATPase was the maximum. In contrast to the case of LaCl₃ addition to culture solution, Ca²⁺-ATPase activity was inhibited by all concentrations of La³⁺ which were added directly to the reaction medium. The above results revealed that REEs inhibited electron transfer from NADH to oxygen in plant plasma membranes, depressed the production of active oxygen radicals, and reduced the formation of lipid peroxides through plasma membrane lipid peroxidation. REEs ions also enhanced the H⁺ extrusion by both standard redox system and H⁺-ATPase in plasma membranes at certain concentrations. A possible role for the plant cell wall in REEs effects on plasma membranes was also suggested.     

Possible Protective Effect of Kolaviron on CCl4-Induced Erythrocyte Damage in Rats

The possible protective effect of kolaviron on rat erythrocytes followingsimultaneous administration of kolaviron (100 mg/kg of body weight/day) withcarbon tetrachloride CCl₄ (1.195 g/kg of body weight/day) by separateintraperitoneal injections was investigated.Kolaviron, a biflavonoid fraction of the defatted alcoholic extract ofGarcinia kola seed, inhibits the accumulation of lipid peroxidationproducts in erythrocytes. A significant reduction (p>0.05) by about34% of lipid peroxidation products was observed in erythrocytes of ratstreated simultaneously with CCl₄ and kolaviron when compared to CCl4-treatedrats. Similarly, the significant increase (p>0.05) in membranecholesterol observed in CCl₄-treated rats was significantly decreased(p>0.05) in rats treated simultaneously with CCl4 andkolaviron. Therefore, there was no significant difference (p>0.05) incholesterol–phospholipid ratio (C/P) of rats treated simultaneouslywith CCl₄ and kolaviron, and the controls. Thus, kolaviron normalizes theCCl₄-induced change in erythrocyte membrane composition.In addition, kolaviron antagonizes the effect of CCl₄ on the activity ofthe membrane bound enzyme, Ca²⁺-ATPase. These results suggest thatkolaviron protects erythrocyte membranes from free radical attack, on bothlipids and proteins.     

Oxidative modifications of cardiac mitochondria and inhibition of cytochrome c oxidase activity by 4-hydroxynonenal

Abstract

4-Hydroxynonenal (HNE) is a highly toxic product of lipid peroxidation (LPO). Its role in the inhibition of cytochrome c oxidase activity and oxidative modifications of mitochondrial lipids and proteins were investigated. The exposure of mitochondria isolated from rat heart to HNE resulted in a time- and concentration-dependent inhibition of cytochrome c oxidase activity with an IC₅₀ value of 8.3 ± 1.0 μM. Immunoprecipitation-Western blot analysis showed the formation of HNE adducts with cytochrome c oxidase subunit I. The loss of cytochrome c oxidase activity was also accompanied by reduced thiol group content and increased HNE-lysine fluorescence. Furthermore, there was a marked increase in conjugated diene formation indicating LPO induction by HNE. Fluorescence measurements revealed the formation of bityrosines and increased surface hydrophobicity of HNE-treated mitochondrial membranes. Superoxide dismutase + catalase and the HO^? radical scavenger mannitol partially prevented inhibition of cytochrome c oxidase activity and formation of bityrosines. These findings suggest that HNE induces formation of reactive oxygen species and its damaging effect on mitochondria involves both formation of HNE–protein adducts and oxidation of membrane lipids and proteins by free radicals.     

Electron transport chain in a thermotolerant yeast

Yeasts capable of growing and surviving at high temperatures are regarded as thermotolerant. For appropriate functioning of cellular processes and cell survival, the maintenance of an optimal redox state is critical of reducing and oxidizing species. We studied mitochondrial functions of the thermotolerant Kluyveromyces marxianus SLP1 and the mesophilic OFF1 yeasts, through the evaluation of its mitochondrial membrane potential (ΔΨ_m), ATPase activity, electron transport chain (ETC) activities, alternative oxidase activity, lipid peroxidation. Mitochondrial membrane potential and the cytoplasmic free Ca²⁺ ions (Ca²⁺ cyt) increased in the SLP1 yeast when exposed to high temperature, compared with the mesophilic yeast OFF1. ATPase activity in the mesophilic yeast diminished 80% when exposed to 40° while the thermotolerant SLP1 showed no change, despite an increase in the mitochondrial lipid peroxidation. The SLP1 thermotolerant yeast exposed to high temperature showed a diminution of 33% of the oxygen consumption in state 4. The uncoupled state 3 of oxygen consumption did not change in the mesophilic yeast when it had an increase of temperature, whereas in the thermotolerant SLP1 yeast resulted in an increase of 2.5 times when yeast were grown at 30^o, while a decrease of 51% was observed when it was exposed to high temperature. The activities of the ETC complexes were diminished in the SLP1 when exposed to high temperature, but also it was distinguished an alternative oxidase activity. Our results suggest that the mitochondria state, particularly ETC state, is an important characteristic of the thermotolerance of the SLP1 yeast strain.     

Inhibition of xanthine oxidase — xanthine — iron mediated lipid peroxidation by eugenol in liposomes

The effect of eugenol on xanthine oxidase (XO) xanthine(X)-Fe⁺³-ADP mediated lipid peroxidation was studied in liver microsomal lipid liposomes. Eugenol inhibited the lipid peroxidation in a dose dependent manner as assessed by formation of thiobarbituric acid reactive substances. When tested for its effect on XO activity per se, (by measuring uric acid formation) eugenol inhibited the enzyme to an extent of 85% at 10 µm concentration and hence formation of O₂ also However, the concentration of eugenol required for XO inhibition was more in presence of metal chelators such as EDTA, EGTA and DETAPAC, but not in presence of deferoxamine, ADP and citrate. The antiperoxidative effect of eugenol was about 35 times more and inhibition of XO was about 5 times higher as compared to the effect of allopurinol. Eugenol did not scavenge O₂ generated by phenazine methosulfate and NAD but inhibited propagation of peroxidation catalyzed by Fe²⁺ EDTA and lipid hydroperoxide containing liposomes. Eugenol inhibits XO-X-Fe⁺³ ADP mediated peroxidation by inhibiting the XO activity per se in addition to quenching various radical species. (Mol Cell Biochem 166: 65-71, 1997)     

Calcium protects <Emphasis Type="Italic">Trifolium repens</Emphasis> L. seedlings against cadmium stress

The effect of calcium (Ca²⁺) on Trifolium repens L. seedlings subjected to cadmium (Cd²⁺) stress was studied by investigating plant growth and changes in activity of antioxidative enzymes. Physiological analysis was carried out on seedlings cultured for 2 weeks on half-strength Hoagland medium with Cd²⁺ concentrations of 0, 400 and 600 μM, and on corresponding medium supplied with CaCl₂ (5 mM). Exposure to increasing Cd²⁺ reduced the fresh weight of the upper part (stems + leaves) of the seedlings more strongly than that of the root system. In both parts of T. repens seedlings H₂O₂ level and lipid peroxidation increased. In the upper part, Cd²⁺ exposure led to a significant decrease in the activity of superoxide dismutase, catalase and glutathione peroxidase and an increase in ascorbate peroxidase activity. In contrast, the roots showed an increase in the activity of antioxidative enzymes under Cd²⁺ stress. Ca²⁺ addition to medium reduced the Cd²⁺ accumulation, and considerably reversed the Cd²⁺-induced decrease in fresh mass as well as the changes in lipid peroxidation in the both parts of T. repens seedlings. Ca²⁺ application diminished the Cd²⁺ effect on the activity of antioxidative enzymes in the upper part, even though it did not significantly affect these enzymes in the roots. So the possible mechanisms for the action of Ca²⁺ in Cd²⁺ stress were considered to reduce Cd²⁺ accumulation, alleviate lipid peroxidation and promote activity of antioxidative enzymes.     

Lack of correlation between TBARS production and PUFA degradation during incubation of membrane erythrocytes in an OH⋅ (Fe2+/H2O2) generator system

We investigated the effects of an OH^⋅ (Fe²⁺/H₂O₂) generator system of erythrocyte membrane, particularly the time-course of lipid peroxidation as estimated by measurement of conjugated dienes, thiobarbituric reactive substances (TBARS), lipofuscin-like pigments, and α-tocopherol. Polyunsaturated fatty acids (PUFAs), especially arachidonic acid (20∶4 ω 6) and docosahexenoic acid (22∶6 ω 3), were also measured. Erythrocyte membranes were suspended in phosphate buffer containing Fe²⁺ (200 μM) and H₂O₂ (1.42 mM), and incubated in a shaking water bath at 37°C. Initially, there was an increase in TBARS and lipofuscin-like pigments, two well-known end products of PUFA oxidative degradation, whereas PUFAs remained unchanged (incubation time: 1 h). After two or more hours of incubation, marked lipid peroxidation was noted, with the appearance of conjugated dienes and a decrease of PUFAs, indicating that lipid peroxidation had occurred after a lag phase during which TBARS were not produced from PUFAs. This suggests that another OH^⋅ target was involved.     

Alterations in calcium homeostasis on lead exposure in rat synaptosomes

The effects of lead on Ca²⁺ homeostasis in nerve terminals was studied. Incubation with leadin vitro stimulated the activity of calmodulin and the maximum effect was observed at 30 M lead, higher concentrations had an inhibitory effect.In vivo exposure to lead increased the activity of calmodulin by 45%. Lead had an inhibitory effect on Ca²⁺ ATPase activity in both calmodulin-rich and calmodulin-depleted synaptic plasma membranes, the IC₅₀ values for inhibition being 13.34 and 16.69 M respectively. Exogenous addition of calmodulin (5 g) and glutathione (1 mM) to calmodulin rich synaptic plasma membranes reversed the inhibition by IC₅₀ concentration of lead.In vivo exposure of lead also significantly reduced the Ca²⁺ ATPase activity, resulting in an increase in intrasynaptosomal calcium. Concomitant with the increase in intrasynaptosomal calcium, lipid peroxidation values also increased significantly in lead-treated animals. In addition lead also had an inhibitory effect on depolarization induced Ca²⁺ uptake and the inhibition was found to be a competitive one. The results sugest that lead exerts its toxic effects by modifications of the intracellular calcium messenger system which would have serious consequences on neuronal functioning.     

Paraquat potentiates iron-induced microsomal lipid peroxidation: modulation by the diet lipid composition

SUMMARY

The study concerns the role of two combined factors—lipid composition of the microsomal membranes and the iron concentration in the incubation medium—in lipid peroxidation catalysed by paraquat (P⁺⁺). Rats were subjected to diets containing 5% lipids composed of either tripalmitin (T), peanut oil/rapeseed oil (v/v) (C) or fish oil (F). The level of polyunsaturated fatty acids in the microsomal membranes was higher in C and F than in T. The level of vitamin E was lowest in F. The activity of the system ‘Cyt P450-NADPH cyt c reductase’ increased in the order T<C<F. The iron concentrations initiating a basal NADPH-dependent lipid peroxidation have been established. p⁺⁺ potentiates this peroxidation due to additional reduction of Fe³⁺ by p^+., rather than by O₂^.- as is usually thought to occur. The sensitivity of the membranes to the potentiating effect of P^{+ +} is mainly determined by a high level of polyunsaturated fatty acids, but also by a low level of the antioxidant vitamin E.     

Antioxidant effect of bovine serum albumin on membrane lipid peroxidation induced by iron chelate and superoxide

Albumin is supposed to be the major antioxidant circulating in blood. This study examined the prevention of membrane lipid peroxidation by bovine serum albumin (BSA). Lipid peroxidation was induced by the exposing of enzymatically generated superoxide radicals to egg yolk phosphatidylcholine liposomes incorporating lipids with different charges in the presence of chelated iron catalysts. We used three kinds of Fe³⁺-chelates, which initiated reactions that were dependent on membrane charge: Fe³⁺-EDTA and Fe³⁺-EGTA catalyzed peroxidation in positively and negatively charged liposomes, respectively, and Fe³⁺-NTA, a renal carcinogen, catalyzed the reaction in liposomes of either charge. Fe³⁺-chelates initiated more lipid peroxidation in liposomes with increased zeta potentials, followed by an increase of their availability for the initiation of the reaction at the membrane surface. BSA inhibits lipid peroxidation by preventing the interaction of iron chelate with membranes, followed by a decrease of its availability in a charge-dependent manner depending on the iron-chelate concentration: one is accompanied and the other is unaccompanied by a change in the membrane charge. The inhibitory effect of BSA in the former at high concentrations of iron chelate would be attributed to its electrostatic binding with oppositely charged membranes. The inhibitory effect in the latter at low concentrations of iron chelate would be caused by BSA binding with iron chelates and keeping them away from membrane surface where lipid peroxidation is initiated. Although these results warrant further in vivo investigation, it was concluded that BSA inhibits membrane lipid peroxidation by decreasing the availability of iron for the initiation of membrane lipid peroxidation, in addition to trapping active oxygens and free radicals.     

Arbuscular mycorrhizal inoculation improves growth and antioxidative response of Jatropha curcas (L.) under Na2SO4 salt stress

This study investigated the effect of arbuscular mycorrhizal (AM) fungal consortia on growth, photosynthetic pigments, solutes concentration (e.g., sugars and proline), and antioxidant responses at different levels of Na₂SO₄ stress (0–0.5%, w:w) in potted culture of Jatropha. Results showed that increasing salt levels caused a significant reduction in survival (%), growth parameters, leaf relative water content (LRWC) (%), and chlorophyll content with an increase in electrolyte leakage (%) and lipid peroxidation of membranes of Jatropha. AM inoculation improved biomass yields as well as other physiological parameters (LRWC (%), chlorophyll, proline, and soluble sugar) of salt-stressed Jatropha over noninoculated plants. Tolerance index of Jatropha was higher with AM fungi than without at all salt levels; however, a decline in its value was recorded with increased salinity levels. AM inoculation also enhanced the activities of antioxidant enzymes (e.g., superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase) and decreased oxidative damage to lipids. In conclusion, results indicate that AM inoculation was capable of alleviating the damage caused by salinity stress on Jatropha plants by reducing lipid peroxidation of membrane and membrane permeability and increasing the accumulation of solutes and antioxidant enzyme activity.     

Functional Consequences of Oxidative Membrane Damage

The interaction of reactive oxygen species with biological membranes is known to produce a great variety of different functional modifications. Part of these modifications may be classified as direct effects. They are due to direct interaction of the reactive species with the molecular machinery under study with a subsequent chemical and functional modification of these molecules. An important part of the observed functional modifications are, however, indirect effects. They are the consequence of an oxidative modification of the environment of biological macromolecules. Lipid peroxidation—via its generation of chemically reactive products—contributes to the loss of cellular functions through the inactivation of membrane enzymes and even of cytoplasmic (i.e., water soluble) proteins. Oxidation of membrane lipids may, however, also increase the efficiency of membrane functions. This was observed for a series of transport systems. Lipid peroxidation was accompanied by activation of certain types of ion channels and ion carriers. The effect is due to an increase of the polarity of the membrane interior by accumulation of polar oxidation products. The concomitant change of the dielectric constant, which may be detected via the increase of the membrane capacitance, facilitates the opening of membrane channels and lowers the inner membrane barrier for the movement of ions across the membrane. The predominant effect, however, at least at a greater extent of lipid peroxidation, is the inhibition of membrane functions. The strong increase of the leak conductance contributes to the depolarization of the membrane potential, it destroys the barrier properties of the membrane and it may finally lead, via an increase of cytoplasmic Ca²⁺ concentration, to cell death. The conclusions were derived from experiments performed with different systems: model systems in planar lipid membranes, native ion channels either reconstituted in lipid membranes or investigated in their natural environment by the patch-clamp method, and two important ion pumps, the Na/K-ATPase and the sarcoplasmic reticulum (SR) Ca-ATPase.