Formation of Filamentous Mn Oxide Particles by the Alphaproteobacterium Bosea sp. Strain BIWAKO-01

Mn-rich filamentous particles present in stratified water environments are considered bacteriogenic; however, little is known about their causative agents. This study investigated the production of these particles by an alphaproteobacterium, Bosea sp. strain BIWAKO-01. Particle formation was promoted in static cultures with slightly viscous medium at pH 6.0?6.3 under low-O₂ conditions. The Mn(II) oxidation in cultures was slower in higher O₂ concentration. These results suggested that pH and O₂ concentration are important factors affecting filamentous Mn particle formation in the Mn(II) oxidizer. Lectin staining followed by fluorescence microscopy revealed the presence of specific carbohydrates in the filamentous structures. In addition, transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, and electron energy loss spectroscopy revealed the structural and spatial associations of Mn with O and C on a nanometer scale in filaments. The results suggested the occurrence of sheet-type Mn oxide likely due to the catalytic activity in exopolymeric substances including acidic polysaccharides.     

Chemiluminescence accompanied by the reaction of acridinium ester and manganese (II)

An acridinium ester (AE) alkaline solution can react with Mn(II) to generate a strong chemiluminescence (CL) centered at 435 nm. The effects of reaction conditions such as pH and Mn(II) concentration on CL intensity were examined. In order to explore the CL mechanism, the effect of oxygen on the CL reaction was examined and an X‐ray photoelectron spectroscopy study of the reaction precipitate was carried out. The results indicated that oxygen participated in the CL reaction and Mn(IV) was the primary product in the system. A possible mechanism was proposed that involved two pathways: (1) dissolved oxygen was reduced to reactive oxygen radicals by Mn(II), these reactive intermediates then reacted with AE to produce excited state acridone; (2) Mn(II) could reduce AE to partly reduced AE, which then reacted with oxygen to form excited state acridone. The reactions of other metal ions with AE were also tested, and only Mn(II) was shown to trigger strong CL emission of AE, which indicated that the system had good selectivity for Mn(II). Copyright © 2014 John Wiley & Sons, Ltd.     

锰氧化菌Bacillus sp. MK3-1的Mn(Ⅱ)氧化特性和除锰能力研究

锰氧化微生物能够将可溶的Mn(II)氧化为不溶的锰氧化物沉淀, 因此在生物除锰研究上具有重要的应用价值。本研究从锰污染土壤中分离到一株锰氧化菌Bacillus sp. MK3-1, 该菌对MnCl2有较高抗性, 其最低抑制浓度(Minimal inhibitory concentration, MIC)为20 mmol/L。实验表明该菌在培养基中Mn(Ⅱ)的去除率高达96%, 同时将其制成固体包埋菌剂应用于含0.15 mmol/L的MnCl2水溶液实验, 结果表明其仍然具有稳定的除锰能力, 去除率为87.12%, 使溶液的终锰浓度符合国家排放标准。扫描电子显微镜观察和能谱分析实验表明, 实验产生的锰氧化物均匀地分布在Bacillus sp. MK3-1的细胞表面, 细胞表面含锰量为19.60% (W/W)。用简并引物扩增目前被认为催化锰氧化的多铜氧化酶基因mnxG, 获得了903 bp的基因片段, 其基因产物与已报道的多铜氧化酶具有86%的同源性。     

Mn(II) complexes of monoanionic bidentate chelators: X-ray crystal structures of Mn(dha)2(CH3OH)2 (Hdha = dehydroacetic acid) and [Mn(ema)2(H2O)]2 · 2H2O (Hema = 2-ethyl-3-hydroxy-4-pyrone)

This report describes synthesis and characterization of bis-ligand Mn(II) complexes of bidentate chelators: maltol (3-hydroxy-2-methyl-4-pyrone), ethylmaltol (2-ethyl-3-hydroxy-4-pyrone), 1,2-dimethyl-3-hydroxy-4-pyridinone (DMHP) and dehydroacetic acid. All four Mn(II) complexes were characterized by elemental analysis, IR, UV/Vis, EPR, cyclic voltammetry, and X-ray crystallography in cases of Mn(dha)₂(CH₃OH)₂ and [Mn(ema)₂(H₂O)]₂ · 2H₂O. The bidentate chelator plays a significant role in the solid state structure of its Mn(II) complex. For example, dha forms the monomeric complex Mn(dha)₂(CH₃OH)₂ while ethylmaltol forms the dimeric complex [Mn(ema)₂(H₂O)]₂. Because of smaller size, maltol ligands in Mn(ma)₂ are able to bridge adjacent Mn(II) centers to give a polymeric structure in solid state. Despite of the difference in their solid state structures, both Mn(ema)₂ and Mn(ma)₂ exist in solution as monomeric Mn(II) species, Mn(ema)₂(H₂O)₂ and Mn(ma)₂(H₂O)₂. This assumption is supported by the similarity in their UV/Vis spectra, EPR data and electrochemical properties. Replacing maltol with DMHP results in a decrease (by ∼100 mV) in the redox potential for the Mn(II)/Mn(III) couple, suggesting that DMHP stabilizes Mn(III) better than maltol. Since Mn(DMHP)₂(H₂O)₂ is readily oxidized to form the more stable Mn(III) complex Mn(DMHP)₃, DMHP has the potential as a chelator for removal of excess Mn(II) from patients with chronic Mn toxicity.     

Cu(II) and Zn(II) ions alter the dynamics and distribution of Mn(II) in cultured chick glial cells

Previous studies revealed that Mn(II) is accumulated in cultured glial cells to concentrations far above those present in whole brain or in culture medium. The data indicated that Mn(II) moves across the plasma membrane into the cytoplasm by facilitated diffusion or counter-ion transport with Ca(II), then into mitochondria by active transport. The fact that 1–10 M Mn(II) ions activate brain glutamine synthetase makes important the regulation of Mn(II) transport in the CNS. Since Cu(II) and Zn(II) caused significant changes in the accumulation of Mn(II) by glia, the mechanisms by which these ions alter the uptake and efflux of Mn(II) ions has been investigated systematically under chemically defined conditions. The kinetics of [⁵⁴MN]-Mn(II) uptake and efflux were determined and compared under four different sets of conditions: no adducts, Cu(II) or Zn(II) added externally, and with cells preloaded with Cu(II) or Zn(II) in the presence and absence of external added metal ions. Zn(II) ions inhibit the initial velocity of Mn(II) uptake, increase total Mn(II) accumulated, but do not alter the rate or extent Mn(II) efflux. Cu(II) ions increase both the initial velocity and the net Mn(II) accumulated by glia, with little effect on rate or extent of Mn(II) efflux. These results predict that increases in Cu(II) or Zn(II) levels may also increase the steady-state levels of Mn(II) in the cytoplasmic fraction of glial cells, which may in turn alter the activity of Mn(II)-sensitive enzymes in this cell compartment.     

Manganese and Arsenic Oxidation Performance of Bacterium-Yunotaki 86 (BY86) from Hokkaido,Japan, and the Bacterium's Phylogeny

We examined the Mn(II) oxidation performance of a bacterium, BY86, collected at Yunotaki Falls Hokkaido, Japan. The bacterium showed rapid oxidation of Mn(II), and brown precipitates containing Mn formed within a few days of incubation. The presence of higher oxidation states of Mn than Mn(II) was ascertained by the UV-vis and XANES sutdy. This bacterium did not oxidize As(III) to As(V) in the absence of Mn. In the presence of Mn, however, As(III) was rapidly oxidized to As(V) on the cell surfaces. These findings indicate that BY86 does not have the ability to directly oxidize As(III) to As(V) within a short period of contact, but indirectly oxidizes it by the Mn oxides generated on the cell surfaces. A phylogenetical study disclosed that BY86 was most closely related to Bacillus cereus with an identity of 99.90%. It is expected that our findings in this study will contribute to the study of Mn(II)-oxidizing bacteria, which play an important role in the biogeochemical cycling of Mn as well as other trace elements including As.     

SodA and manganese are essential for resistance to oxidative stress in growing and sporulating cells of Bacillus subtilis

We constructed a sodA-disrupted mutant of Bacillus subtilis 168, BK1, by homologous recombination. The mutant was not able to grow in minimal medium without Mn(II). The spore-forming ability of strain BK1 was significantly lower in Mn(II)-depleted medium than that of the wild-type strain. These deleterious effects caused by the sodA mutation were reversed when an excess of Mn(II) was used to supplement the medium. Moreover, the growth inhibition by superoxide generators in strain BK1 and its parent strain was also reversed by the supplementation with excess Mn(II). We therefore estimated the Mn-dependent superoxide-scavenging activity in BK1 cells. Whereas BK1 cells have no detectable superoxide dismutase (Sod) on native gel, the superoxide-scavenging activity in crude extracts of BK1 cells grown in Mn(II)-supplemented LB medium (10 g of tryptone, 5 g of yeast extract, and 5 g of NaCl per liter) was significantly detected by the modified Sod assay method without using EDTA. The results obtained suggest that Mn, as a free ion or a complex with some cellular component, can catalyze the elimination of superoxide and that both SodA and Mn(II) are involved not only in the superoxide resistance of vegetative cells but also in sporulation.     

SOD-like activity of Mn(II) beta-octabromo-meso-tetrakis(N-methylpyridinium-3-yl)porphyrin equals that of the enzyme itself

Mn porphyrins are among the most efficient SOD mimics with potency approaching that of SOD enzymes. The most potent ones, Mn(III) N-alkylpyridylporphyrins bear positive charges in a close proximity to the metal site, affording thermodynamic and kinetic facilitation for the reaction with negatively charged superoxide. The addition of electron-withdrawing bromines onto beta-pyrrolic positions dramatically improves thermodynamic facilitation for the O2*- dismutation. We have previously characterized the para isomer, Mn(II)Br(8)TM-4-PyP(4+) [Mn(II) beta-octabromo-meso-tetrakis(N-methylpyridinium-4-yl)porphyrin]. Herein we fully characterized its meta analogue, Mn(II)Br(8)TM-3-PyP(4+) with respect to UV/vis spectroscopy, electron spray mass spectrometry, electrochemistry, O2*- dismutation, metal-ligand stability, and the ability to protect SOD-deficient Escherichia coli in comparison with its para analogue. The increased electron-deficiency of the metal center stabilizes Mn in its +2 oxidation state. The metal-centered Mn(III)/Mn(II) reduction potential, E((1/2))=+468 mV vs NHE, is increased by 416 mV with respect to non-brominated analogue, Mn(III)TM-3-PyP(5+) and is only 12 mV less positive than for para isomer. Yet, the complex is significantly more stable towards the loss of metal than its para analogue. As expected, based on the structure-activity relationships, an increase in E((1/2)) results in a higher catalytic rate constant for the O2*- dismutation, log k(cat)> or =8.85; 1.5-fold increase with respect to the para isomer. The IC(50) was calculated to be < or =3.7 nM. Manipulation of the electron-deficiency of a cationic porphyrin resulted, therefore, in the highest k(cat) ever reported for a metalloporphyrin, being essentially identical to the k(cat) of superoxide dismutases (log k(cat)=8.84-9.30). The positive kinetic salt effect points to the unexpected, unique and first time recorded behavior of Mn beta-octabrominated porphyrins when compared to other Mn porphyrins studied thus far. When species of opposing charges react, the increase in ionic strength invariably results in the decreased rate constant; with brominated porphyrins the opposite was found to be true. The effect is 3.5-fold greater with meta than with para isomer, which is discussed with respect to the closer proximity of the quaternary nitrogens of the meta isomer to the metal center than that of the para isomer. The potency of Mn(II)Br(8)TM-3-PyP(4+) was corroborated by in vivo studies, where 500 nM allows SOD-deficient E. coli to grow >60% of the growth of wild type; at concentrations > or =5 microM it exhibits toxicity. Our work shows that exceptionally high k(cat) for the O2*- disproportionation can be achieved not only with an N(5)-type coordination motif, as rationalized previously for aza crown ether (cyclic polyamines) complexes, but also with a N(4)-type motif as in the Mn porphyrin case; both motifs sharing "up-down-up-down" steric arrangement.     

耐辐射球菌基因DR1709与DR2523的突变分析

摘要：【目的】检测在耐辐射球菌抵抗外来辐射和氧自由基的过程中,锰离子转运蛋白基因（DR1709和DR2523）是否发挥了作用。探讨锰离子、锰离子转运蛋白基因与耐辐射球菌辐射抗性之间的关系。【方法】分别构建这两个基因的突变体。对突变体和野生型进行紫外线照射和过氧化氢处理。对处理后的菌株存活率进行分析。【结果】DR2523被突变以后,耐辐射球菌在tryptone-glucose-yeast extract (TGY)培养液中的生长受影响很小。而DR1709突变体M1709在对数生长阶段的生长速度远低于野生型。     

Concurrent Removal of Mn(II) and Cr(VI) by Achromobacter sp. TY3-4

In this study, we report a bacterium, Achromobacter sp. TY3-4, capable of concurrently removing Mn (II) and Cr (VI) under oxic condition. TY3-4 reduced as much as 2.31?mM of Cr (VI) to Cr (III) in 70?h, and oxidized as much as 20?mM of Mn(II) to Mn oxides in 80?h. When 0.58?mM Cr (VI) and 10?mM Mn(II) were present together, both Cr(VI) and Mn(II) were completely removed by TY3-4 and the generated precipitates are Mn^IIIOOH, Mn^III,IV₃O₄, Mn^IVO₂ and Cr^III(OH)₃. Experiments also show that both biosroption and bioreduction of Mn(II) are the driving forces for Mn(II) removal, whereas bioreduction of Cr(VI) is the driving force for Cr(VI) removal. On the basis of these results, a possible reaction was proposed that TY3-4 concurrently reduces Cr(VI) and oxidizes Mn(II). This study is fundamental for Mn and Cr cycles. The strain shows potential for practical application.     

Microbial Community Analysis and Effects of Fe(II)/Mn(II) Ratio on Denitrification in the Mixotrophic Biological Reactor

In this study, the denitrification performance of the mixotrophic biological reactor was investigated under varying Fe(II)/Mn(II) molar ratio conditions. Results indicate that the optimal nitrate removal ratio occurred at an Fe(II)/Mn(II) molar ratio of 9:1, pH of 7, with an HRT of 10?h. When the reactor was performing under optimal conditions, the nitrate removal reached 100.00% at a rate of 0.116?mmol·L^?1·h^?1. The proportion of oxidized Fe(II) and Mn(II) reached 99.29% and 21.88%, respectively. High-throughput sequencing results show that Pseudomonas was the dominant species in the mixotrophic biological reactor. Furthermore, the relative abundance of Pseudomonas and denitrification performance was significantly influenced by variation in the Fe(II)/Mn(II) molar ratio.     

Differential response of salt-marsh species to variation of iron and manganese

Salt-marsh plants of the lower, middle and upper marsh were compared in their response to iron and manganese. The species studied showed differential sensitivity to high concentrations of Fe (1 000 μM) and Mn (10 000 μM) in hydroculture experiments, species of the lower marsh being more resistant than species of the upper marsh. Fe and Mn concentrations in the root were higher than in the shoot, which was also found in plants inundated with seawater. High Fe and Mn concentrations in the root are probably the result of the oxidizing power of plant roots with a subsequent low translocation of Fe (II) and Mn (II) to the shoot. At high (toxic) Fe and Mn levels in the nutrient solution, Fe and Mn concentrations were much higher in the shoots of sensitive species than in resistant species. The P content of roots and shoots was not influenced by increased Fe and Mn concentrations. Fe and Mn resistance in Spartina anglica and Juncus gerardii, may be in part due to a high root porosity. Other species, however, that are similarly resistant to Fe and Mn lack a well-developed aerenchym. Root porosity, radial oxygen loss and Fe (II) and Mn (II) exclusion by oxidation to Fe (III) (hydr)oxides deposited on the roots form part of the resistance mechanism of hygrohalophytes to Fe and Mn; the differences in this respect between the species may also be due to other metabolic aspects.     

Comparison of the SOD-like activity of hexacoordinate Mn(II), Fe(II) and Ni(II) complexes having isoindoline-based ligands

Recently, a series of Fe(II) complexes have been published by our group with 3 N-donor 1,3-bis(2′-Ar-imino)isoindoline ligands containing various Ar-groups (pyridyl, 4-methylpyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl). The superoxide scavenging activity of the compounds showed correlation with the Fe(III)/Fe(II) redox potentials. Analogous, electroneutral chelate complexes with Mn(II) and Ni(II) in 2:1 ligand:metal composition are reported here. Each Mn(II) complex exhibits one reversible redox wave that is assigned as the Mn(III)/Mn(II) redox transition. The E_1/2 spans a 180 mV range from − 98 (Ar = 3-methylpyridyl) to 82 mV (Ar = thiazolyl) vs. the Fc⁺/Fc depending on the Ar-sidearm. The SOD-like (SOD=superoxide dismutase)activity of all complexes was determined according to the McCord-Fridovich method. The Mn(II) isoindolinates have IC₅₀ values - determined with 50 μM cytochrome c Fe(III) - that range from (3.22 ± 0.39) × 10^− 6 (Ar = benzimidazolyl) to (10.80 ± 0.54) × 10^− 6 M (Ar = N-methylbenzimidazolyl). In contrast with the Fe(II) complexes, the IC₅₀ concentrations show no significant dependence on the E_1/2 values in this narrow potential range emphasizing that the redox potential is not the governing factor in the Mn(II)-containing scavengers. The analogous Ni(II) compounds show no redox transitions in the thermodynamically relevant potential range (− 0.40 to 0.65 V vs. SCE) and accordingly, their superoxide scavenging activity (if any) is below the detection level.     

Induction of superoxide dismutases in Escherichia coli by manganese and iron.

Growth of Escherichia coli B in simple media enriched with Mn(II) resulted in the elevation of the manganese-containing superoxide dismutase, whereas growth in such medium enriched with iron caused increased content of the iron-containing superoxide dismutase. Enrichment of the medium with Co(II), Cu(II), Mo(VI), Zn(II), or Ni(II) had no effect. The inductions of superoxide dismutase by Mn(II) or by Fe(II) were dioxygen dependent, but these metals did not affect the CN- -resistant respiration of E. coli B and did not influence the increase in the CN- -resistant respiration caused by paraquat. Mn(II) and paraquat acted synergistically in elevating the superoxide dismutase content, and Mn(II) reduced the growth inhibition imposed by paraquat, E. coli grown in the complex 3% Trypticase soy broth (BBL Microbiology Systems)-0.5% yeast extract-0.2% glucose medium contained more superoxide dismutase than did cells grown in the simple media and were less responsive to enrichment of the medium with Mn(II) or Fe(II). Nevertheless, in the presence of paraquat, inductions of superoxide dismutase by these metals could be seen even in the Trypticase-yeast extract-glucose medium. On the basis of these observations we propose that the apo-superoxide dismutases may act as autogenous repressors and that Mn(II) and Fe(II) increase the cell content of the corresponding enzymes by speeding the conversion of the apo- to the holoenzymes.     

Topology of NH2OH-induced Mn(II) release from chloroplast thylakoid membranes

Permeant and impermeant metal ion chelators have been used in conjunction with NMR relaxation time measurements (T₁) of solvent protons to probe the membrane topology of the Mn(II) released from the water-oxidizing center of chloroplast thylakoid membranes by NH₂OH. Chelex, a tightly binding divalent metal ion exchanger, quantitatively removes Mn²⁺ (added as MnCl₂) from the external thylakoid membrane without significantly affecting oxygen evolution activity or photophosphorylation efficiency. Because of its obvious impermeance (the resin is supplied as 0.2 mm beads), chelex selectively removes only manganese that is in equilibrium with the external aqueous phase. Both internal and external manganese pools are removed by chelex in the presence of A23187, a divalent cation-specific ionophore. Topological experiments using these reagents have shown that NH₂OH releases Mn(II) predominantly to the loculus in freshly prepared, dark-adapted thylakoid membranes at 0–3°C. This topology changes radically as a result of three pretreatments: (1) incubation of thylakoid membranes in the dark at 25°C, which redirects Mn(II) release toward the external medium with a half-time of 10–15 min; (2) illumination with saturating white light, which decreases the half-time of reorientation to about 1 min; (3) freeze-thawing in 0.4 M sucrose, which results in the appearance of 40–60% of the NH₂OH-liberated Mn(II) in the external medium. None of these treatments substantially degrades O₂ evolution activity or osmotic integrity as judged from measurements of photophosphorylation efficiency. It is concluded that the topology of the manganese site associated with photosystem II is not static but changes dramatically in response to external stimuli, possibly reflecting a regulatory mechanism of photophosphorylation.     

Optimization of Nitrate and Manganese Removal by Bacterium Pseudomonas sp. H117 in Mixotrophic Condition

Previous study has revealed that Pseudomonas sp. H117 could exhibit excellent performance on autotrophic and heterotrophic denitrification in polluted groundwater. However, a novel character of simultaneous denitrification and manganese removal by the bacteria remained to be further explored. In this study, we investigated optimum conditions of nitrate and Mn(II) removal by the strain H117 in mixotrophic condition. Different factors (temperature, initial pH, nitrate concentration, and Mn(II) concentration) were investigated and optimized by response surface methodology (RSM), demonstrating that the highest nitrate removal ratio (100%) in the mixotrophic condition occurred at the temperature of 30.20?°C, pH of 6.90, and Mn(II) concentration of 61.81?mg/l. Meanwhile, the optimal Mn(II) removal (73.34%) conditions were at the temperature of 29.33?°C, pH of 7.22, and nitrate concentration of 20.74?mg/l. Furthermore, microbial development pattern, cellular metabolites, and bioprecipitation were characterized by the excitation emission matrix (EEM), meteorological chromatography analysis, and scanning electron microscopy (SEM) methods, respectively. These results demonstrated that strain H117 can have good adaptability to the environment, thus exhibiting an efficient ability for bioremediation of groundwater polluted by nitrate and Mn(II).     

Catalytic superoxide scavenging by metal complexes of the calcium chelator EGTA and contrast agent EHPG

Metal ion chelators widely used in experimental protocols and clinical diagnosis are generally assumed to be inert. We previously reported that the ubiquitous chelator EDTA has high levels of superoxide suppressing activity. Here, we report that the common chelators calcium chelator EGTA and contrast agent EHPG have significant activities in suppressing superoxide levels depending on the nature of metal ion chelated. The most active species is Mn(II)-EGTA which exhibited an IC50 value of 0.19 microM for superoxide destruction. In addition, IC50 values for Mn(II)-EHPG and 2Cu(II)-EGTA were 0.69 and 0.60 microM, respectively. In conclusion, Mn(II) and Cu(II) complexes of the common chelators EGTA and EHPG exhibit considerable superoxide scavenging activities. Caution should be employed in their use in biological systems where superoxide has a key role and they may be useful for the development of catalytic anti-oxidants.     

Intracellular Mn (II)-associated superoxide scavenging activity protects Cu,Zn superoxide dismutase-deficient Saccharomyces cerevisiae against dioxygen stress

Three Cu,Zn superoxide dismutase (SOD-1)-deficient Saccharomyces cerevisiae mutants do not grow in 100% O2 in rich medium and require Met and Lys when grown in air (Bilinski, T., Krawiec, Z., Liczmanski, A., and Litwinska, J. (1985) Biochem. Biophys. Res. Commun. 130, 533-539). We show herein that medium manganese (II) accumulated by the mutants rescues these O2-sensitive phenotypes; 2 mM medium Mn2+ represented the threshold required for cell growth. The accumulation of Mn2+ was not oxygen-inducible since mutants grown aerobically and anaerobically accumulated the same amount of Mn2+. Mn2+ accumulation is not unique to these mutants since wild type accumulated almost twice as much Mn2+ as did mutant. ESR spectra of the cell extracts and whole cells loaded with Mn2+ were typical of free Mn(II) ion. These spectra could not account quantitatively for the total cellular Mn2+, however. A screen for soluble antioxidant activities in the Mn2+-supplemented cells detected O2- (superoxide) scavenging activity, with no change in catalase or peroxidase activities. This O2- scavenging activity was CN- and heat-resistant. No achromatic bands were revealed in nondenaturing gels of Mn2+- containing cell extracts stained for O2- scavenging activity. The Mn2+-dependent O2- scavenging activity in the cell extracts was quenched by EDTA and dialyzable. More than 60% of both the intracellular Mn2+ and the O2- scavenging activity was removed by 2-h dialysis. Dialyzed cells were not viable in air unless resupplemented with either Met or Mn2+. Although Mn2+ supported the aerobic growth of these mutants, excess Mn2+, which correlated with an elevated O2- scavenging activity, was toxic to both mutant and wild type. The results indicate that free or loosely bound Mn2+ ion protects the mutants against oxygen stress by providing an intracellular, presumably cytosolic, O2- scavenging activity which replaces the absent SOD-1.     

Role of the 33-kDa polypeptide in preserving Mn in the photosynthetic oxygen-evolution system and its replacement by chloride ions

Treatment of Photosystem II particles from spinach chloroplasts with Triton X-100 with 2.6 M urea in the presence of 200 mM NaCl removed 3 polypeptides of 33 kDa, 24 kDa and 18 kDa, but left Mn bound to the particles. The (urea + NaCl)-treated particles could evolve oxygen in 200 mM, but not in 10 mM NaCl. Mn was gradually released with concomitant loss of oxygen-evolution activity in 10 mM NaCl but not in 200 mM Cl^?. The NaCl-treated particles, which contained Mn and the 33-kDa polypeptide but not the 24-kDa and 18-kDa polypeptides, did not lose Mn or oxygen-evolution activity in 10 mM NaCl. These observations suggest that the 33-kDa polypeptide maintains the binding of Mn to the oxygen-evolution system and can be functionally replaced by 200 mM Cl^?.     

Rice tolerance to excess Mn: Implications in the chloroplast lamellae and synthesis of a novel Mn protein

Rice (Oryza sativa L. cv. Safari) plants were grown over a 21-d period in nutrient solutions containing Mn concentrations varying between 0.125 and 32 mg·L^–1. The plant shoots and the thylakoid membranes showed similar overall Mn increases for this range of treatments, but different accumulation kinetics. It was found that the highest Mn treatment were associated to the synthesis of a new thylakoid protein with an average molecular mass of 36.5 kDa and a Mn:protein ratio of about 1. This protein exhibited superoxide dismutase activity, as well as a high content of Gln, Asp, Glu, Leu and Gly. Its EPR spectrum is characteristic of high-spin Mn(II), in a S=5/2 ground state. A comparative study of SDS polyacrylamide gel profiles of thylakoid polypeptides from the various treatments disclosed quantitative changes, as well as a new 37/36-kDa polypeptide band in the two highest Mn treatments. The photosynthetic electron transport rates coupled to PSII and PSI showed a significant increase until the 8-mg·L^–1 Mn treatment. The related superoxide production of thylakoids (monitored by EPR spectroscopy) showed minimum values from the 0.5-mg·L^–1 Mn treatment onwards, which, as shown by the thiobarbituric acid reaction was coupled to a non-significant variation of the acyl lipid peroxidation. It was concluded that Oryza sativa L. cv. safari has a high internal tolerance to Mn as it synthesises a new manganese protein that mimics superoxide dismutase functioning.