Effect of Some Environmental Pollutants on the Superoxide Dismutase Activity in Lemna

Exposure of Lemma sp. to SO₂ resulted in an increased activity of superoxide dismutase. About 3 to 4 fold increase in the activity was observed within 30 minutes after the plants were fumigated with 10 ml/l of SO₂. Paraquat, a well known superoxide generator, doubled the enzyme activity after 1 hour of treatment with 0.1 mM paraquat. Superoxide dismutase activity was also enhanced by cadmium treatment but the response was not immediate. Optimum increase in the activity of enzyme was observed after 4 days of treatment with 40 mg/l of cadmium in the medium. Treatment with H₂O₂ very clearly inhibited the activity of superoxide dismutase in Lemna.     

镉胁迫小海绵羊肚菌氧化损伤及其抗氧化防御

羊肚菌Morchella是全球广泛分布的食药用真菌,重金属镉(Cd)在羊肚菌中的积累受到越来越多的关注。然而,羊肚菌镉积累的机理尚不清楚。本研究通过在0–5.0mg/LCd浓度环境中培养小海绵羊肚菌Morchella spongiola,测定Cd胁迫下其菌丝生长速率、丙二醛(MDA)、过氧化氢(H₂O₂)、超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、谷胱甘肽过氧化物酶(GSH-Px)、谷胱甘肽(GSH)、抗坏血酸(ASA)及细胞Cd积累量等生理生化指标,旨在明晰小海绵羊肚菌响应Cd毒害的抗氧化防御响应机理。结果表明随着Cd浓度的增加,小海绵羊肚菌菌丝生长呈现出“升-降-升-降”的双峰响应变化,其中0.15、0.90和1.50 mg/L为菌丝生长Cd浓度关键拐点。Cd胁迫导致的氧化损伤与其初始浓度呈现正相关,胁迫3 d时MDA和H₂O₂含量显示出较大提升,5.0 mg/L处理组MDA和H₂O₂含量比对照组分别高出5.80倍和6.08...     

不同钙浓度对宽叶雀稗幼苗的生长和抗性生理的影响

研究不同钙浓度对宽叶雀稗(Paspalum wettsteinii)幼苗生长和生理的影响, 对于揭示宽叶雀稗对不同钙浓度环境的适应机理至关重要。该研究采用盆栽砂培试验, 研究不同钙浓度(0、5、25、50、100和200 mmol·L^-1 CaCl₂)和不同处理时间(7、14、21和28天)对宽叶雀稗幼苗生长、渗透调节物质含量、抗氧化酶活性、叶绿素含量和光合参数的影响。结果表明, 随着CaCl₂浓度的增加和处理时间的延长, 宽叶雀稗幼苗株高等形态指标、生物量、渗透调节物质含量、抗氧化酶活性、叶绿素含量和光合参数呈先增后减的趋势, 低钙浓度(5-50 mmol·L^-1)环境下, 株高、叶长、叶宽、根长和生物量与对照(0 mmol·L^-1)相比均升高, 脯氨酸、可溶性蛋白和可溶性糖含量、过氧化物酶、过氧化氢酶和超氧化物歧化酶活性提高, 丙二醛含量和胞间CO₂浓度降低、叶绿素含量增加以及净光合速率、蒸腾速率和气孔导度增强; 高钙浓度(200 mmol·L^-1)环境下, 脯氨酸、可溶性蛋白和可溶性糖含量、过氧化物酶、过氧化氢酶和超氧化物歧化酶活性降低, 丙二醛含量和胞间CO₂浓度增加, 叶绿素含量减少以及净光合速率、蒸腾速率和气孔导度减弱。结合隶属函数分析, 低钙盐浓度(5-50 mmol·L^-1)处理对宽叶雀稗幼苗无抑制作用, 说明宽叶雀稗对低钙浓度具有一定的耐受性; 而在高钙浓度(200 mmol·L^-1)下, 宽叶雀稗幼苗通过提高自身有机渗透调节物质含量、增强酶活性、增加叶绿素含量以及增强光合作用等方式来快速调节植物生理代谢功能, 进而适应高钙浓度环境条件。     

Phenotypic analysis of the ccp1Delta and ccp1Delta-ccp1W191F mutant strains of Saccharomyces cerevisiae indicates that cytochrome c peroxidase functions in oxidative-stress signaling

Yeast cytochrome c peroxidase (CCP) efficiently catalyzes the reduction of H₂O₂ to H₂O by ferrocytochrome c in vitro. The physiological function of CCP, a heme peroxidase that is targeted to the mitochondrial intermembrane space of Saccharomyces cerevisiae, is not known. CCP1-null-mutant cells in the W303-1B genetic background (ccp1Δ) grew as well as wild-type cells with glucose, ethanol, glycerol or lactate as carbon sources but with a shorter initial doubling time. Monitoring growth over 10 days demonstrated that CCP1 does not enhance mitochondrial function in unstressed cells. No role for CCP1 was apparent in cells exposed to heat stress under aerobic or anaerobic conditions. However, the detoxification function of CCP protected respiring mitochondria when cells were challenged with H₂O₂. Transformation of ccp1Δ with ccp1^W191F, which encodes the CCP^W191F mutant enzyme lacking CCP activity, significantly increased the sensitivity to H₂O₂ of exponential-phase fermenting cells. In contrast, stationary-phase (7-day) ccp1Δ-ccp1^W191F exhibited wild-type tolerance to H₂O₂, which exceeded that of ccp1Δ. Challenge with H₂O₂ caused increased CCP, superoxide dismutase and catalase antioxidant enzyme activities (but not glutathione reductase activity) in exponentially growing cells and decreased antioxidant activities in stationary-phase cells. Although unstressed stationary-phase ccp1Δ exhibited the highest catalase and glutathione reductase activities, a greater loss of these antioxidant activities was observed on H₂O₂ exposure in ccp1Δ than in ccp1Δ-ccp1^W191F and wild-type cells. The phenotypic differences reported here between the ccp1Δ and ccp1Δ-ccp1^W191F strains lacking CCP activity provide strong evidence that CCP has separate antioxidant and signaling functions in yeast.     

Antioxidant enzyme activity and lipid peroxidation in liver of female rats co-exposed to lead and cadmium: effects of vitamin E and Mn2+

The oxidative status of liver of female rats exposed to lead acetate and cadmium acetate either alone or in combination at a dose of 0.05 mg/kg body wt intraperitoneally for 15 days was studied. After the administration of lead alone, the activity of superoxide dismutase (SOD) decreased in liver, whereas no changes were observed in catalase (CAT) activity, and glutathione (GSH) and thiobarbituric acid (TBARS) levels. Cadmium exposure and combined exposure to lead and cadmium led to decrease in GSH content and increased TBARS levels. Moreover, animals exposed to either cadmium alone or in combination with lead showed a decrease in SOD activity and an increase in CAT activity. The in vitro experiments showed that vitamin E failed to restore the antioxidant enzyme activities in metal treated postmitochondrial supernatant fraction of liver. But Mn²⁺ ions protected the mitochondria from lipid peroxidation and could completely restore Mn-superoxide dismutase (Mn-SOD) activity following metal intoxication. The results of this study indicate that despite the ability of lead and cadmium to induce oxidative stress the effect in liver is not intensified by combined exposure to both lead and cadmium. The observed changes in various oxidative stress parameters in the liver of rats co-exposed to lead and cadmium may result from an independent effect of lead and /cadmium and also from their interaction such as changes in metal accumulation and content of essential elements like Cu, Zn and Fe. These results suggest that when lead and cadmium are present together in similar concentrations, cadmium mediates major effects due to its more reactive nature.     

深圳7种园林植物叶绿素荧光特性及其对大气SO2浓度的响应

叶绿素荧光信号能快速灵敏地反映植物生理状态及其与环境的关系,是一种理想光系统探针。测定了深圳市7种园林植物叶片的叶绿素荧光参数和叶绿素含量,并对这些生理参数与大气污染物SO₂的相关性进行了分析。结果表明,7种植物叶片的叶绿素含量具有明显的种间差别,生境的差别远小于种间差别。所测定的7种园林植物的F_v/F_m相差不大,平均为0.78,低于理想条件下的最大值,说明存在一定的生长胁迫。叶绿素荧光的光化学淬灭qP的种间差别不明显。非光化学猝灭系数qN的种类差别较大,白兰Michelia alba和短穗鱼尾葵Caryota mitis具有较高的非光化学淬灭能力,说明这两个种具有一定的光保护能力。7种植物中,白兰的ΦpsⅡ要明显地较低于其它植物。深圳大气污染对城区植物的生理生化特性尚未构成不良影响,在深圳市区的环境中,短穗鱼尾葵、勒杜鹃Bougainvillea spectabilis和阴香Cinnamomum burmanii的叶绿素荧光参数可以作为大气污染物的指示指标;大红花Hibiscus rosa-sinensis、九里香Murraga paniculata、白兰和黄叶假连翘Duranta cv Golden Leaves具有相对较高抗污染物的能力。植物的叶绿素荧光参数也在一定程度上受到叶绿素的影响,阴香、短穗鱼尾葵、大红花和九里香的部分叶绿素荧光参数与植物叶片叶绿素含量呈正相关。     

Age-related changes in antioxidant enzyme activities and lipid peroxidation in lungs of control and sulfur dioxide exposed rats

Antioxidant defenses within the lung are pivotal in preventing damage from oxidative toxicants. There have also been several reports with conflicting results on the antioxidant system during aging. In this study, we attempted to investigate age-related alterations in both antioxidant enzyme activities and thiobarbituric acid-reactive substances (TBARS), a product of lipid peroxidation, in the whole lung of control and sulfur dioxide (SO₂) exposed rats of different age groups (3-, 12-, and 24-months-old). Swiss-Albino Male rats were exposed to 10 ppm SO₂ 1 hr/day, 7 days/week for 6 weeks. The antioxidant enzymes examined include Cu,Zn-superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST). A mixed pattern of age-associated alterations in antioxidant activities was observed. SOD, GSH-Px and GST activities were increased with age, but CAT activity was decreased. Lung SOD, GSH-Px and GST activities were also increased in response to SO₂. The level of TBARS was increased with age. SO₂ exposure stimulated lipid peroxide formation in the lung as indicated by an increase in the level of TBARS. These findings suggest that both aging and SO₂ exposure may impose an oxidative stress to the body. We conclude that the increase in the activities of the antioxidant enzymes of the lung during aging, could be interpreted as a positive feedback mechanism in response to rising lipid peroxidation.     

硫污染对9种园林植物叶片硫含量与叶绿素荧光参数的影响

对深圳市9种园林植物叶片硫含量,以及硫处理对叶片光合作用参数的影响进行了初步研究。这9种植物分别为红背桂(Excoccaria cochinchinensis)、黄脉爵床(Sanchezia nobilis)、大叶变叶木(Codiaeum variegatum)、基及树(Saruma henryi)、短穗鱼尾葵(Caryota mitis)、小叶榕(Ficus microcarpa var.pusillifolia)、高山榕(Ficus altissima)、海桐(Pittosporum tobira)和黄叶假连翘(Duranta repenscv.\'Dwarf Yellow\')。在温度25℃条件下分别在光照和黑暗条件,用NaHSO₃和蒸馏水浸泡各植物叶圆片24h,共形成4种处理。采用PAM-2100荧光仪测定叶绿素荧光参数。在自然状况下采集的黄脉爵床叶片含硫量最高,远高于其他植物,具有较高的富集能力,含量最低的是大叶变叶木。用蒸馏水浸泡后,9种植物叶片的硫含量的变化很少。在NaHSO₃处理下,有7种植物叶片的硫含量显著提高,增加最多的是自然条件下富集能力最低的大叶变叶木。[0]取自不同大气SO₂污染环境的被测试植物显示,除海桐外,小南山的其它8种植物叶片含硫量都大于世博园植物叶片的含硫量。小南山9种植物的F_v/F_m值也都低于世博园,说明在污染较严重的情况下可以通过测定植物叶片的F_v/F_m值来进行现场监测。     

镉胁迫对大青杨不同倍体的生长及生理生化的影响

以大青杨不同倍体当年生扦插苗为研究对象，用不同浓度CdCl₂溶液对其进行镉胁迫处理，研究不同镉浓度对大青杨3种倍体的生长和生理生化的影响。结果表明：镉胁迫对大青杨3种倍体生长有显著的抑制作用，随着镉浓度的增加，与对照苗（二倍体，CK）相比受胁迫苗的苗高和地径都显著下降；叶绿素含量先升高后下降；大青杨二倍体和四倍体的叶片含水量随镉浓度增加呈下降趋势，而三倍体叶片含水量则在低浓度时增加，高浓度时降低；三倍体和四倍体的过氧化氢酶（CAT）和超氧化物歧化酶（SOD）的酶活性在镉浓度低时增加，在镉浓度高时降低，而二倍体中酶活性则呈下降趋势。这说明镉浓度低时3种倍体都有较好的耐受性，而在高浓度胁迫下三倍体含水量、叶绿素含量、CAT的活性和丙二醛（MDA）含量比四倍体分别高5.47%、25.47%、8.59%、28.47%，比二倍体分别高23.47%、44.63%、17.23%、31.48%，说明大青杨三倍体在镉胁迫下细胞膜损伤最小，抗氧化能力最强，有较好的抗重金属镉的能力。本研究为在重金属污染地区进行育种工作提供了理论依据。     

The response of sweet corn to HF and SO2 under field conditions

“Marcorss” sweet corn plants grown in field plots were exposed continuously in open-top chambers for 32 days to ambient air, charcoal-filtered air or charcoal-filtered air containing HF (ca. 0.5 μgF m⁻³), SO₂ (ca. 235 μg m⁻³), or the two pollutants combined. Elliptical chlorotic leasions appeared after 23 days on leaves of plants exposed to SO₂/HF, and shortly thereafter on plants exposed to all other treatments. At harvest, the number of plants with lesions was significantly greater in chambers supplied with SO₂/HF than in chambers with SO₂, HF, or filtered air.

The different treatments had no effect on fresh or dry weights of leaves, husks, or tassels, height of plants, or number of kernels per ear. Exposure to SO₂/HF reduced the fresh and dry weights of stalks. There were fewer mature ears in the SO₂/HF and unfiltered air treatments than in the others. The reduction in yield from SO₂/HF was about the same as that ascribed to ambient photochemical oxidants in the unfiltered air treatment.

HF combined with SO₂ had no effect on accumulation of S as compared with SO₂ alone, but there was a striking reduction in accumulation of foliar F in plants exposed to SO₂/HF as compared with HF alone.     

不同氧浓度下C2C12细胞的Nrf2抗氧化系统对H2O2刺激的反应*

目的:探讨不同氧浓度下小鼠骨骼肌卫星细胞系(C2C12细胞)对H₂O₂刺激反应的变化及其机制。方法:小鼠骨骼肌卫星细胞系(C2C12细胞),经培养复苏后,将细胞分为7组,每组设8个复孔,各组分别加入浓度为0.1 mmol/L、0.25 mmol/L、0.5 mmol/L、0.75 mmol/L、1 mmol/L、2 mmol/L的H₂O₂,分别作用1 h、2 h后测细胞活力,选择细胞H₂O₂刺激的最佳作用时间和浓度;C2C12细胞分为不同氧浓度组:21% O₂、12% O₂、8% O₂、5% O₂每组设8个复孔,12 h后,H₂O₂作用1 h,收集细胞;检测细胞Nrf2蛋白荧光和蛋白表达量,测定Nrf2和抗氧化酶SOD1、SOD2、CAT、NQO-1、HO-1、GPX-1 的mRNA表达量及细胞ROS水平。结果:选择H₂O₂作用时间相对较短的1 h和浓度0.5 mmol/L作为本实验的H₂O₂刺激条件。与21%O₂组相比,12%O₂组细胞Nrf2蛋白荧光增强,Nrf2 的mRNA和蛋白表达以及抗氧化酶SOD1、SOD2、CAT、NQO-1、HO-1、GPX-1的 mRNA表达均显著增加(P＜0.05或P＜0.01),细胞 ROS水平明显降低(P＜0.01);8%O₂组仅GPX-1 mRNA显著增加(P＜0.05),其他指标变化不大;5%O₂组细胞 Nrf2 mRNA和蛋白表达以及抗氧化酶SOD1、SOD2、NQO-1、GPX-1的 mRNA表达均明显降低(P＜0.05或P＜0.01),细胞 ROS水平则明显升高(P＜0.01)。结论:不同氧浓度下C2C12细胞中Nrf2介导的抗氧化系统对H₂O₂刺激反应不同,12 h的12% O₂浓度可促进C2C12细胞Nrf2的抗氧化作用,而5% O₂浓度的严重低氧则作用相反。     

The presence of a SO molecule in [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki as detected by mass spectrometry

The active site of [NiFe] hydrogenase is a binuclear metal complex composed of Fe and Ni atoms and is called the Ni–Fe site, where the Fe atom is known to be coordinated to three diatomic ligands. Two mass spectrometric techniques, pyrolysis-MS (pyrolysis-mass spectrometry) and TOF-SIMS (time-of-flight secondary ion mass spectrometry), were applied to several proteins, including native and denatured forms of [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F, [Fe₄S₄]₂-ferredoxin from Clostridium pasteurianum, [Fe₂S₂]-ferredoxin from Spirulina platensis, and porcine pepsin. Pyrolysis-MS revealed that only native hydrogenase liberated SO/SO₂ (ions of m/z 48 and 64 at an equilibrium ratio of SO and SO₂) at relatively low temperatures before the covalent bonds in the polypeptide moiety started to decompose. TOF-SIMS indicated that native Miyazaki hydrogenase released SO/SO₂ (m/z 47.97 and 63.96) as secondary ions when irradiated with a high-energy Ga⁺ beam. Denatured hydrogenase, clostridial ferredoxin, and pepsin did not release SO as a secondary ion. The FT-IR spectrum of the enzyme suggested the presence of CO and CN. These lines of evidence suggest that the three diatomic ligands coordinated to the Fe atom at the Ni–Fe site in Miyazaki hydrogenase are SO, CO, and CN. The role of the SO ligand in helping to cleave H₂ molecules at the active site and stabilizing the Fe atom in the diamagnetic Fe(II) state in the redox cycle of this enzyme is discussed.     

Effect of carbon dioxide on antioxidant enzymes and ginsenoside production in root suspension cultures of Panax ginseng

The aim of this study was to investigate the effect of CO₂ at various concentrations (1, 2.5 and 5%) on antioxidant enzymes and ginsenoside accumulation in Panax ginseng roots in 5 l airlift bioreactors (working volume 4 l). One and 2.5% CO₂ was beneficial for root biomass accumulation, but 5% CO₂ decreased the biomass. Ginsenoside concentration decreased with increasing concentration of CO₂. No significant difference was observed in the malondialdehyde (MDA) content and lipoxygenase (LOX) activity between respective controls and CO₂ treated roots. Antioxidant enzymes such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), catalase (CAT), guaiacol peroxidase (G-POD) including reduced ascorbate and total glutathione were induced in CO₂ exposed roots which emphasized the protective role of antioxidants against CO₂ induced stress. Superoxide dismutase activity (SOD) which was induced after 15 days was significantly inhibited after 45 days. Glutathione-S-transferase (GST) and glutathione peroxidase (GPX) activities also increased when the roots were subjected to 1 and 2.5% CO₂ compared to the respective controls but not at 5%. A higher reduced ascorbate to oxidized (ASC/DHA) ratio in CO₂ treated root indicates the plant's ability to tolerate CO₂ stress. These observations suggest that an increase in antioxidant enzymes may affect a defense response to the cellular damage induced by CO₂. Probably, this increase could not stop the deleterious effects of CO₂ concentration on ginsenoside concentration, but reduced stress severity and thereby allowing root growth to occur.     

Purification and partial characterization of Cu, Zn containing superoxide dismutase from entomogenous fungal species Cordyceps militaris

Cordyceps militaris mycelium produced mainly Cu, Zn containing superoxide dismutase (Cu, Zn-SOD). Cu, Zn-SOD activity was detectable in the culture filtrates, and intracellular Cu, Zn-SOD activity as a proportion protein was highest in early log phase culture. The effects of Cu²⁺, Zn²⁺, Mn²⁺ and Fe²⁺ on enzyme biosynthesis were studied. The Cu, Zn-SOD was isolated and purified to homogeneity from C. militaris mycelium and partially characterized. The purification was performed through four steps: (NH₄)₂SO₄ precipitation, DEAE-sepharose™ fast flow anion-exchange chromatography, CM-650 cation-exchange chromatography, and Sephadex G-100 gel filtration chromatography. The purified enzyme had a molecular weight of 35070 ± 400 Da and consisted of two equal-sized subunits each having a Cu and Zn element. Isoelectric point value of 7.0 was obtained for the purified enzyme. The N-terminal amino acid sequence of the purified enzyme was determined for 12 amino acid residues and the sequences was compared with other Cu, Zn-SODs. The optimum pH of the purified enzyme was obtained to be 8.2–8.8. The purified enzyme remained stable at pH 5.8–9.8, 25 °C and up to 50 °C at pH 7.8 for 1.5 h incubation. The purified enzyme was sensitive to H₂O₂, KCN. 2.5 mM NaN₃, PMSF, Triton X-100, β-mercaptoethanol and DTT showed no significant inhibition effect on the purified enzyme within 5 h incubation period.     

盐胁迫下解钾菌对枸杞幼苗的促生效应

以‘宁杞1号’枸杞为研究对象,采用单因素随机区组试验设计,研究不添加NaCl和菌剂(CK)、100 mmol·L^-1 NaCl胁迫(NaCl)、100 mmol·L^-1 NaCl胁迫下添加解钾菌KSBGY01单菌液(NaCl-M1)、KSBGY02单菌液(NaCl-M2)及其混合菌液(NaCl-M3)对枸杞幼苗叶片叶绿素、多酚、超氧阴离子(O₂^-·)、过氧化氢(H₂O₂)和可溶性糖含量、抗氧化物酶和蔗糖代谢酶活性的影响,以探索解钾菌对盐胁迫下枸杞生理生化特性的影响。结果表明: 盐胁迫下解钾菌能够提高枸杞叶片类黄酮(FLAV)、荧光激发比花青素相对指数(FERARI)、花青素(ANTH-RB)和氮素平衡指数(NBI-G),降低O₂^-·和H₂O₂含量,增加可溶性糖含量及过氧化氢酶(CAT)、蔗糖磷酸合成酶(SPS)、蔗糖合成酶(SS)和转化酶(INV)活性。不同处理间比较,NaCl-M2处理中枸杞叶片ANTH-RB值、NBI-G值、可溶性糖含量及CAT、SPS、SS和INV活性最高;NaCl-M3处理中枸杞叶片叶绿素含量、FLAV和FERARI值最高;NaCl-M1处理中枸杞叶片超氧化物歧化酶(SOD)活性最高;不添加解钾菌的NaCl处理中枸杞叶片谷胱甘肽过氧化物酶(GSH-Px)活性最高;CK处理中枸杞叶片过氧化物酶(POD)活性最高。对枸杞幼苗14项生理生化指标进行灰色系统关联度分析表明,盐胁迫条件下添加解钾菌处理的枸杞生理生化指标加权关联度均高于CK和NaCl处理,其中NaCl-M2处理的加权关联度最高。因此,添加KSBGY02单菌液更有利于缓解盐胁迫对枸杞幼苗的影响。     

Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2)

Kinetic results are reported for intramolecular PPh₃ substitution reactions of Mo(CO)₂(η¹-L)(PPh₃)₂(SO₂) to form Mo(CO)₂(η²-L)(PPh₃)(SO₂) (L = DMPE = (Me)₂PC₂H₄P(Me)₂ and dppe=Ph₂PC₂H₄PPh₂) in THF solvent, and for intermolecular SO₂ substitutions in Mo(CO)₃(η²-L)(η²-SO₂) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH₂Cl₂ solvent. Activation parameters for intramolecular PPh₃ substitution reactions: ΔH^≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS^≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO₂ in MO(CO)₃(η²-L)(η²-SO₂) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO₂ to accept a pair of electrons from the metal, with its bonding transformations of η²-SO₂ to η¹-pyramidal SO₂, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)₂(dmpe)(PPh₃)(SO₂) was determined crystallographically: P2₁/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) ų, Z=4, R(F)=3.49%.     

Lethality of hydrogen peroxide in wild type and superoxide dismutase mutants of Escherichia coli. (A hypothesis on the mechanism of H2O2-induced inactivation of Escherichia coli)

The toxicity of H₂O₂ in Escherichia coli wild type and superoxide dismutase mutants was investigated under different experimental conditions. Cells were either grown aerobically, and then treated in M9 salts or K medium, or grown anoxically, and then treated in K medium. Results have demonstrated that the wild type and superoxide dismutase mutants display a markedly different sensitivity to both modes of lethality produced by H₂O₂ (i.e. mode one killing, which is produced by concentrations of H₂O₂ lower than 5 mM, and mode two killing which results from the insult generated by concentrations of H₂O₂ higher than 10 mM). Although the data obtained do not clarify the molecular basis of H₂O₂ toxicity and/or do not explain the specific function of superoxide ions in H₂O₂-induced bacterial inactivation, they certainly demonstrate that the latter species plays a key role in both modes of H₂O₂ lethality. A mechanism of H₂O₂ toxicity in E. coli is proposed, involving the action of a hypothetical enzyme which should work as an O₂^-• generating system. This enzyme should be active at low concentrations of H₂O₂ (<5 mM) and high concentrations of the oxidant (>5 mM) should inactivate the same enzyme. Superoxide ions would then be produced and result in mode one lethality. The resistance at intermediate H₂O₂ concentrations may be dependent on the inactivation of such enzyme with no superoxide ions being produced at levels of H₂O₂ in the range 5–10 mM. Mode two killing could be produced by the hydroxyl radical in concert with superoxide ions, chemically produced via the reaction of high concentrations of H₂O₂ (>10 mM) with hydroxyl radicals. The rate of hydroxyl radical production may be increased by the higher availability of Fe²⁺ since superoxide ions may also reduce trivalent iron to the divalent form.     

Relationship between active oxygen species and cardenolide production in cell cultures of Digitalis thapsi: effect of calcium restriction

Elimination of calcium ions from the medium of undifferentiated cell cultures of Digitalis thapsi increased cardenolide production and induced extracellular H₂O₂ accumulation, as measured by the quenching of pyranine fluorescence. The addition of catalase reduced the response and the inclusion of superoxide dismutase enhanced the loss of fluorescence. This suggested that, besides H₂O₂, the superoxide anion was also formed before dismutating to H₂O₂. Additionally, exogenous H₂O₂ or superoxide dismutase stimulated cardenolide production whereas the addition of catalase markedly reduced it. These results point to a connection between H₂O₂ and cardenolide formation. The absence of calcium did not alter the levels of lipid peroxidation products; however, changes in the antioxidant system of D. thapsi cells were observed. Catalase activity was extremely low in control cultures and remained unaltered upon calcium elimination. Ascorbate peroxidase activity was not modified in calcium-free cultures. By contrast, calcium deprivation stimulated superoxide dismutase activity and strongly inhibited glutathione reductase activity. Also, a significant decrease in reduced glutathione was observed. These responses were emulated by treatment of the cultures with the glutathione biosynthesis inhibitor buthionine sulfoximine and by ethyleneglycol-bis-β-aminoethyl ether and LaCl₃. All these results indicate that the depletion of extracellular calcium induces changes in the redox state of cells and suggest that this alteration stimulates cardenolide formation in D. thapsi cultures.     

Changes in lipid peroxidation, superoxide dismutase activity, ascorbic acid and phospholipid content in liver of freshwater catfish Heteropneustes fossilis exposed to elevated temperature

1. 1. Lipid peroxidation, superoxide dismutase (SOD) activity, ascorbic acid (AsA) and individual phospholipid contents in liver of fresh water cat fish Heteropneustes fossilis were measured after exposure to different temperatures (25, 27, 32, 37°C) at various times (1–4 h).

2. 2. Lipid peroxidation and superoxide dismutase activity were significantly increased with increases in temperature at various times.

3. 3. Ascorbic acid content was depleted when temperature was increased.

4. 4. After temperature exposure, phosphatidyl inositol was increased while phosphatidyl choline, phosphatidyl serine and phosphatidyl ethanolamine were depleted. Phosphatidic acid level did not change.

5. 5. The findings indicated an increased oxidative stress in liver following increases in temperature at various times. Concurrent with the increase in lipid peroxidation, superoxide dismutase activity and ascorbic acid from the liver of fish varied. It is suggested that depletion of major individual phospholipids following temperature exposure could be due to superoxide created oxidative stress in the liver.