Battles with iron: manganese in oxidative stress protection

The redox-active metal manganese plays a key role in cellular adaptation to oxidative stress. As a cofactor for manganese superoxide dismutase or through formation of non-proteinaceous manganese antioxidants, this metal can combat oxidative damage without deleterious side effects of Fenton chemistry. In either case, the antioxidant properties of manganese are vulnerable to iron. Cellular pools of iron can outcompete manganese for binding to manganese superoxide dismutase, and through Fenton chemistry, iron may counteract the benefits of non-proteinaceous manganese antioxidants. In this minireview, we highlight ways in which cells maximize the efficacy of manganese as an antioxidant in the midst of pro-oxidant iron.     

Studies on the manganese uptake of lettuce on steam-sterilised glasshouse soils

Summary During steam sterilisation of glasshouse soils appreciable amounts of easily reducible manganese are converted into exchangeable manganese. The reverse process takes place much more gradually. As a result, manganese toxicity occurs in several crops on newly steamed soils. In the Netherlands, lettuce has been found to be particularly prone to manganese toxicity. An investigation was carried out to obtain more information about the manganese status of steamed glasshouse soils in which lettuce was used as the test crop. The following results were noted.The uptake of exchangeable manganese is easier in the lighter soils than in heavy soils. Application of iron to the soil inhibits manganese uptake by the plant, but the iron must be applied in the form of chelate. The pH has a profound effect on manganese uptake on steamed as well as on unsteamed soils. However, the relationship between the pH and the manganese content of the crop on steamed soils is different from that found on unsteamed soils.The slow rate of oxidation of manganese in steamed glasshouse soil may be explained by the fact that the oxidising bacteria are killed during the steam sterilisation process. The fixation of manganese can be accelerated appreciably by inoculating the steamed soil with manganese-oxidising bacteria.The effect on manganese uptake of five soil desinfection chemicals used in the investigation proved to be very small.The lettuce varieties used in the Netherlands show a wide variation in susceptibility to manganese toxicity. This cannot be explained by different rates of manganese uptake. It is more likely that the varietal differences are based on different levels of resistance to manganese present in the plants.     

Manganese deficiency in sugar beet and the incorporation of manganese in the coating of pelleted seed

Summary A laboratory study, three glasshouse tests and eight field experiments on commercial farms in East Anglia during 1972 to 1974 tested the effect of incorporating manganese in the coating of pelleted seed on the manganese nutrition and yield of sugar beet. The pelleting material readily absorbed manganese from solution but most of the manganese was held in plant-available forms. Tests in the glasshouse showed that manganese sulphate or manganous oxide were likely to be the most effective seed-pellet additives, but manganese sulphate was harmful to sugar beet in slightly acid potting compost.Incorporating manganous oxide in the pellet prevented early symptoms of deficiency on sugar beet in field experiments and replaced an early foliar spray but the plants developed manganese deficiency later. The treatment was an economic and effective method of supplying manganese to sugar-beet seedlings too small to spray but, should manganese deficiency be prolonged, the plants will need spraying when large enough.     

Regulation of Manganese Accumulation and Exchange in Bacillus subtilis W23

An overnight culture of Bacillus subtilis W23 in low-manganese tryptone broth is unable to sporulate and becomes hyperactive with regard to the manganese active transport system during stationary phase. When manganese is added to cells in spent or fresh medium, the cells immediately accumulate a high proportion of the manganese available in the medium. When the hyperactive cells are diluted into broth containing 10 muM Mn(2+), high intracellular manganese levels are reached, and inhibition of ribonucleic acid and protein synthesis occurs. This inhibition is relieved when the intracellular manganese concentration declines to the nontoxic levels characteristic of cells growing in 10 muM Mn(2+). The release of the accumulated manganese is achieved by a reduction in the uptake rate for manganese while the efflux rate remains essentially constant. Inhibitors of ribonucleic acid and protein synthesis prevent the reduction of the high rate of manganese uptake and, therefore, high net concentrations of manganese are maintained in the presence of these inhibitors. The hyperactive manganese uptake system is temperature dependent and inhibited by cyanide and m-chlorophenyl carbonylcyanide hydrazone.     

The effect of high dose oral manganese exposure on copper,iron and zinc levels in rats

Manganese is an essential dietary nutrient and trace element with important roles in mammalian development, metabolism, and antioxidant defense. In healthy individuals, gastrointestinal absorption and hepatobiliary excretion are tightly regulated to maintain systemic manganese concentrations at physiologic levels. Interactions of manganese with other essential metals following high dose ingestion are incompletely understood. We previously reported that gavage manganese exposure in rats resulted in higher tissue manganese concentrations when compared with equivalent dietary or drinking water manganese exposures. In this study, we performed follow-up evaluations to determine whether oral manganese exposure perturbs iron, copper, or zinc tissue concentrations. Rats were exposed to a control diet with 10 ppm manganese or dietary, drinking water, or gavage exposure to approximately 11.1?mg manganese/kg body weight/day for 7 or 61 exposure days. While manganese exposure affected levels of all metals, particularly in the frontal cortex and liver, copper levels were most prominently affected. This result suggests an under-appreciated effect of manganese exposure on copper homeostasis which may contribute to our understanding of the pathophysiology of manganese toxicity.     

Down-Regulation of a Manganese Transporter in the Face of Metal Toxicity

The yeast Smf1p Nramp manganese transporter is posttranslationally regulated by environmental manganese. Smf1p is stabilized at the cell surface with manganese starvation, but is largely degraded in the vacuole with physiological manganese through a mechanism involving the Rsp5p adaptor complex Bsd2p/Tre1p/Tre2p. We now describe an additional level of Smf1p regulation that occurs with toxicity from manganese, but not other essential metals. This regulation is largely Smf1p-specific. As with physiological manganese, toxic manganese triggers vacuolar degradation of Smf1p by trafficking through the multivesicular body. However, regulation by toxic manganese does not involve Bsd2p/Tre1p/Tre2p. Toxic manganese triggers both endocytosis of cell surface Smf1p and vacuolar targeting of intracellular Smf1p through the exocytic pathway. Notably, the kinetics of vacuolar targeting for Smf1p are relatively slow with toxic manganese and require prolonged exposures to the metal. Down-regulation of Smf1p by toxic manganese does not require transport activity of Smf1p, whereas such transport activity is needed for Smf1p regulation by manganese starvation. Furthermore, the responses to manganese starvation and manganese toxicity involve separate cellular compartments. We provide evidence that manganese starvation is sensed within the lumen of the secretory pathway, whereas manganese toxicity is sensed within an extra-Golgi/cytosolic compartment of the cell.     

On the effect of ferrous sulphate on the available manganese in the soil and the uptake of manganese by the plant II

Summary Pot experiments with oats on manganese deficient sandy and moor soils, which are not deficient in iron, showed a steady increase in yield and manganese uptake by the plants with increasing additions of ferrous sulphate at four levels of manganese. Residual effects from ferrous sulphate application were not found either in the case of yields or manganese uptake by oats on a sandy soil.The effect observed following application of ferrous sulphate was due to a manganese effect. This is corroborated by the coincidence of the yield curves, showing the relationship between absorbed manganese and yield of dry matter, following the application of manganese sulphate and ferrous sulphate.Soils treated withM magnesium nitrate in the presence of equivalent quantities of either ferrous sulphate or hydroquinone yielded the same amounts of manganese. This result suggests that the manganese effect of ferrous sulphate is due to reduction of higher manganese oxides by ferrous sulphate.     

Intestinal transport of manganese from human milk, bovine milk and infant formula in rats

The transport of manganese from extrinsically labeled human milk, bovine milk and infant formula was studied by the everted intestinal sac method. Tissue/mucosal flux data indicated that transport of manganese into the intestinal tissue was significantly greater with bovine milk and formula than from human milk. Similarly, the total flux of manganese from the mucosal to serosal surface was less when human milk was used. Smaller molecular weight manganese binding ligands isolated from the milk samples enhanced the mucosal to tissue movement of manganese as contrasted to the higher molecular weight manganese binding ligands. Most significantly the data suggest that the transport and uptake of manganese is less in the presence of human milk and its isolated manganese fractions than it is in bovine milk or infant formula.     

Manganese binding to the prion protein

There is considerable evidence that the prion protein binds copper. However, there have also been suggestions that prion protein (PrP) binds manganese. We used isothermal titration calorimetry to identify the manganese binding sites in wild-type mouse PrP. The protein showed two manganese binding sites with affinities that would bind manganese at concentrations of 63 and 200 mum at pH 5.5. This indicates that PrP binds manganese with affinity similar to other known manganese-binding proteins. Further study indicated that the main manganese binding site is associated with His-95 in the so-called "fifth site" normally associated with copper binding. Additionally, it was shown that occupancy by copper does not prevent manganese binding. Under these conditions, manganese binding resulted in an altered conformation of PrP, displacement of copper, and altered redox chemistry of the metal-protein complex. Cyclic voltammetric measurements suggested a complex redox chemistry involving manganese bound to PrP, whereas copper-bound PrP was able to undergo fully reversible electron cycling. Additionally, manganese binding to PrP converted it to a form able to catalyze aggregation of metal-free PrP. These results further support the notion that manganese binding could cause a conformation change in PrP and trigger changes in the protein similar to those associated with prion disease.     

On the effect of ferrous sulphate on the available manganese in the soil and the uptake of manganese by the plant

Summary Application of iron as ferrous sulphate or chloride to a loam not deficient in manganese had no effect on the yield but increased the uptake of manganese even in barley which grew vigorously.In an experiment with sugar beet on two soils contrasted with regard to their available manganese supply, applications of manganese, iron and nitrogen were tested in all combinations. On the Købelev soil, not deficient in manganese, no increases in yields were obtained on addition of ferrous sulphate while increases in manganese uptake were found for all combinations of treatments except where iron was added in the presence of manganese.On the manganese deficient Faarevejle soil, significantly higher increases in yields of roots were obtained from ferrous sulphate in the presence of nitrogen than in the presence of manganese. The effect of iron in the presence of nitrogen on the yield of tops was also significant. These treatments also gave the highest increases in manganese uptake.The amounts of manganese extractable from the soils by magnesium nitrate over a range of pH 2–8 could be increased considerably by addition of ferrous sulphate.The results support the suggestion that application of ferrous sulphate to some soils has the same effect as an addition of manganese.     

Interaction of manganese II ions with proteins

Electron and ESR-spectroscopic study was carried out of the interaction between manganese(II) ions with albumine and lysozome in water solutions at different manganese concentrations and ratios manganese/protein. The results obtained suggest presence of metal-protein interactions. At high manganese concentrations liotropic effect is observed. At high molecular ratios protein/manganese and manganese concentrations close to physiological ones formation of coordination compounds manganes(II) ions with proteins was observed.     

Manganese-phosphate reactions in aqueous systems and the effects of applications of monocalcium phosphate,on the availability of manganese to oats in an alkaline fen soil

Summary Electrometric titrations and chemical analyses of aqueous systems containing manganese sulphate and phosphoric acid showed that the compositions of manganese phosphates formed at various pH values depended on initial manganese concentrations and Mn : P molar ratios. The results show how phosphate benefits crops on soils containing toxic levesl of manganese.A pot experiment measured the effects of monocalcium phosphate, in the presence or absence of extra manganese, on the availability to oats of manganese in an alkaline manganese-deficient soil. On such a soil, phosphate equivalent to 750 or 1500 pounds of superphosphate per acre is unlikely to enhance manganese availability; such dressings may lessen grain yields considerably.Neutral and alkaline manganese-deficient fen soils were incubated with monocalcium-phosphate with and without added manganese salts. The phosphate dressings had only small effects on soil pH and on exchangeable and readily reducible manganese.     

Manganese Transport in Bacillus subtilis W23 During Growth and Sporulation

Manganese is accumulated in Bacillus subtilis by a highly specific active transport system. This trace element "pump" is insensitive to added magnesium or calcium and preferentially accumulates manganese in the presence of cobalt, iron, and copper. Manganese uptake in B. subtilis is inhibited by cyanide, azide, pentachlorophenol, and m-chlorophenyl carbonylcyanide hydrazone. The uptake of manganese follows Michaelis-Menten kinetics, and the net accumulation of manganese is regulated by increasing the V(max) after exposure to manganese-starvation conditions and by decreasing the V(max) for manganese uptake during growth in excess manganese. The K(m) remains constant during these regulatory changes in V(max). Manganese accumulated during growth is exchangeable for exogenous manganese and can be released from the cells by toluene (which causes leakage but not lysis) or by lysis with lysozyme. Two stages can be distinguished with regard to intracellular manganese during the process of growth and sporulation. During logarithmic growth, B. subtilis maintains a relatively constant internal manganese content, which is a function of the external manganese concentration following approximately a Langmuir adsorption isotherm. At the end of log phase, net accumulation of manganese slows. A second phase of net manganese accumulation begins at about the same time during sporulation as the accumulation of calcium begins. The manganese accumulated during growth and early sporulation is exchangeable and therefore relatively "free"; intracellular manganese is converted later during sporulation into a bound form that cannot be released by toluene or lysozyme.     

Coordination between manganese and nitrogen within the ligands in the manganese complexes facilitates the reconstitution of the water-oxidizing complex in manganese-depleted photosystem II preparations

The water-oxidizing complex (WOC) within photosystem II (PSII) can be reconstituted with synthetic manganese complexes by a process called photoactivation; however, the key factors affecting the efficiency of synthetic manganese complexes in reconstitution of electron transport and oxygen evolution activity in manganese-depleted PSII remain unclear. In the present study, four complexes with different manganese coordination environments were used to reconstitute the WOC, and an interesting relationship was found between the coordination environment of the manganese atom in the complexes and their efficiency in restoring electron transport and oxygen evolution. If Mn(II) is coordinated to nitrogen atoms within the ligand, it can restore significant rates of electron transport and oxygen evolution; however, if the manganese atom is coordinated only to oxygen atoms instead of nitrogen atoms, it has no capability to restore electron transport and oxygen evolution. So, our results demonstrate that the capability of manganese complexes to reconstitute the WOC is mainly determined by the coordination between nitrogen atoms from ligands and the manganese atom. It is suggested from our results that the ligation between the nitrogen atom and the manganese atom within the manganese complex facilitates the photoligation of the manganese atom to histidyl residues on the apo-protein in manganese-depleted PSII during photoactivation.     

Influence of potassium and manganese on growth and uptake of magnesium by soybeans (Glycine max (L.) Merr. cv. Bragg)

Summary Soybean (Glycine max (L) Merr. cv. Bragg) seedlings were grown in nutrient solutions to evaluate the response to manganese nutrition as affected by potassium supply. In solutions containing 275 M manganese, increasing the solution concentration of potassium from 1 mM to 10 mM alleviated symptoms of manganese toxicity, decreased manganese concentrations in the leaves and increased dry matter yields of the plants. The reduction in manganese toxicity was brought about by a reduced rate of root absorption of manganese at high potassium supply levels.Increasing the supply of either potassium or manganese decreased the leaf concentration of magnesium although there were no apparent symptoms of magnesium deficiency in any treatment. The reduced concentration of magnesium in the leaves was due to effects of potassium and manganese on the rate of root absorption of magnesium.Under manganese deficiency conditions, growth was reduced and manganese concentrations in plant parts were very low; there was no effect of potassium supply when manganese was absent from the nutrient solution.     

锰有效性对大豆锰、铁和磷吸收及其分布的影响

本文研究外源锰有效性对大豆生长和锰、铁、磷吸收及其分布影响的结果表明,在锰缺乏和锰浓度超过50μmol·L-1的处理条件下,大豆生长受到明显抑制。随着外源锰浓度增加,大豆体内,尤其在老叶中锰浓度显著增加。锰和铁之间存在一定的拮抗作用。缺锰和锰毒不影响大豆对磷的吸收。但是,缺锰显著影响磷在老叶和新叶中的分配。     

A light-dependent mechanism for massive accumulation of manganese in the photosynthetic bacterium Synechocystis sp. PCC 6803

Manganese is an essential micronutrient for many organisms. Because of its unique role in the water oxidizing activity of photosystem II, manganese is required for photosynthetic growth in plants and cyanobacteria. Here we report on the mechanism of manganese uptake in the cyanobacterium Synechocystis sp. PCC 6803. Cells grown in 9 microM manganese-containing medium accumulate up to 1 x 10(8) manganese atoms/cell, bound to the outer membrane (pool A). This pool could be released by EDTA treatment. Accumulation of manganese in pool A was energized by photosynthetic electron flow. Moreover, collapsing the membrane potential resulted in the immediate release of this manganese pool. The manganese in this pool is mainly Mn(II) in a six-coordinate distorted environment. A distinctly different pool of manganese, pool B ( approximately 1.5 x 10(6) atoms/cell), could not be extracted by EDTA. Transport into pool B was light-independent and could be detected only under limiting manganese concentrations (1 nM). Evidently, manganese uptake in Synechocystis 6803 cells occurs in two steps. First, manganese accumulates in the outer membrane (pool A) in a membrane potential-dependent process. Next, manganese is transported through the inner membrane into pool B. We propose that pool A serves as a store that allows the cells to overcome transient limitations in manganese in the environment.     

Active transport at the blood-CSF barrier contributes to manganese influx into the brain

Manganese is an essential trace element, and a contrast agent of potential interest for brain magnetic resonance imaging. Brain overexposure to manganese, however induces a neurodegenerative syndrome. Imaging data suggest that manganese appearance into the CSF precedes its accumulation into the cerebral parenchyma. We therefore investigated manganese uptake and transport at the blood-CSF barrier. Like lead, the non protein-bound divalent manganese accumulated into the rat choroid plexus. The metal accumulation was especially high in developing animals. Using a differentiated cellular model of the blood-CSF barrier, we demonstrated that manganese crosses the choroid plexus epithelium by a concentrating, unidirectional blood-to-CSF transport mechanism. This transport was inhibited by calcium, which is also transported into the CSF against its concentration gradient. The permeability barrier function towards lipid-insoluble compound and the organic anion transport property of the blood-brain interface were affected by exposure of the blood-facing membrane of choroidal cells to micromolar concentrations of manganese, but its antioxidant capacity was not. The unidirectional transport of manganese across the choroid plexus provides the anatomo-functional basis linking the systemic exposure to manganese with the spreading pattern of manganese accumulation observed in brain imaging, and explains the polarized sensitivity of choroidal epithelial cells to manganese toxicity.