Free Fe2 Research Articles

Characterization of the micro-environment of Salmonella typhimurium-containing vacuoles within MDCK epithelial cells.

Salmonella typhimurium has the capacity to enter into and multiply within epithelial cells. During the entire intracellular stage, bacteria are enclosed within a vacuole. To characterize the micro-environment of the bacteria-containing vacuoles, we have used a new method to measure the expression levels of several S. typhimurium genes in intracellular bacteria within Madin-Darby canine kidney (MDCK) epithelial cells. Our study was based on the determination of beta-galactosidase activity derived from lacZ transcriptional fusions using the highly sensitive substrate fluorescein-di-beta-D-galactoside (FDG). Expression of the iroA and mgtB genes (induced by Fe2+ and Mg2+ limitation respectively), and cadA (induced by pH 6.0 in the presence of lysine, with enhanced expression under anaerobiosis) were characterized at different post-infection times. High intracellular expression levels were detected for the iroA and mgtB genes, suggesting that the concentrations of free Fe2+ and Mg2+ in the vacuole may be low. cadA activity was detected only at early post-infection times (4 h), suggesting that the vacuole may have a mild-acidic pH, and oxygen and lysine present at this time. Globally, the results reported indicate that the use of a highly sensitive beta-galactosidase substrate can provide information about the micro-environment within which an intracellular pathogen, such as S. typhimurium, resides.

Covalency in FeF2 from magnetisation density data and from ab initio theory

A further analysis of the polarised neutron diffraction data on FeF2 has been carried out using a valence orbital population model of the spin density. The fit to the data, chi 2=1.8 for all reflections, is considerably better than for ligand field models used previously. The improvement is traced to the fact that the new model emphasises covalent interaction between iron and fluorine, whereas the earlier treatments introduced it only after spin-orbit interactions within the free Fe2+ ion had been taken into account. The amount of covalence required to explain the results is considerable, at least 10% of the spin of the iron atom being delocalised. However, the amount of spin seen on each fluorine atom is not correspondingly large, because cancellation takes place on account of the antiferromagnetic nature of the compound. An ab initio approximate calculation carried out on FeF64-, units using the DV-Xalpha method lends strong support to the picture introduced by the valence orbital population model, and confirms that there are strong elements of covalence in the Fe-F interaction.

Magnetic and crystallographic characterization of Zn0.78Fe0.22Se and FeSe films on GaAs (001)

We have grown single-crystal (001) epilayers of the diluted magnetic semiconductor Zn1−xFexSe with 0≤x≤1 on GaAs(001) substrates by molecular-beam epitaxy. The films retain the zinc-blende structure for thicknesses up to at least 2 μm for x≤0.22, while epilayers with higher Fe concentrations can be stabilized up to some decreasing critical thickness. SQUID magnetometry data obtained for x=0.22 indicate Van Vleck paramagnetic behavior accompanied by a decrease in the fraction of magnetically free Fe2+ ions with increasing x. Conversion electron Mössbauer spectra of the FeSe epilayers show a dominant paramagnetic central peak at both 300 and 13.5 K, with small contributions from Zeeman-split components at low temperature. The samples were further characterized with x-ray rocking curve, θ-2θ, and topography measurements.

<i>tert</i>.-Butylhydroperoxide 処理による赤ビート切片からのベタシアニン リーケージに及ぼす各種の添加物質の影響

With the purpose of getting much information about the mechanism of leakage observed at the onset of plant senescence or other physiological disorders, a model system using red beet discs has been investigated in our study. The present paper describes the effects of various chemicals added to the incubation medium, in which red beet discs are exposed or pre-exposed to tert. -butylhydroperoxide (BHP), on the leakage of red betacyanin pigment from the cells. The mechanism of betacyanin leakage induced by the BHP treatment is suggested from these results.1. Under the same conditions reported in our previous paper, the treatment with BHP (10mM and 8hrs) evidently caused the abrupt increase of OD 540nm (leakage of red betacyanin pigment), and the optical density reached about 1.0 from 5hrs to 7hrs after the treatment.2. The addition of 5mM sodium diethyldithiocarba mate, 20mM thiourea, 5.0mM (+)-catechin and 1mM n-propyl gallate, separately, to the incubation medium effectively inhibited the increase in OD 540nm, when each chemical and BHP were added simultaneously.3. L-Cysteine (5mM) and D-ascorbic acid (5mM), which are well known as endogenous reducing agents, also showed the inhibitory effect on Betacyanin leakage of red beet discs.4. When (+)-catechin (5mM), cysteine (10mM) and thiourea (20mM) wereadded, separately, to the incubation medium in the absence of BHP after the BHP treatment (10mM and 8hrs), they also showed significant effects on inhibition of betacyanin leakage.5. The presence of 5mM EDTA or 2.5mM FeCl3 in the incubation medium containing 10mM BHP enhanced the increase in OD 540nm considerably.These results suggest that BHP taken into the discs of red beet, as indicated in the red cells of human blood, may be transformed by either free Fe3+, chelated Fe3+ or other endogenous unknown factors to the tert. -butoxyl radical, and consequently will attack various biomembranes in the cells to cause the lakage of red betacyanin pigment. Further biochemical investigation will be required to confirm the mechanism.

Biogeochemical Conditions Favoring Magnetite Formation during Anaerobic Iron Reduction

Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe was released into the growth medium. Geochemical equilibrium equations with E(h) and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local E(h) and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or abiological oxidation-reduction reactions).

Iron oxidation in Mops buffer. Effect of EDTA, hydrogen peroxide and FeCl3.

The effect of EDTA and H2O2 on iron autoxidation in Mops buffer depends on the pH of the solution. At acidic pH, EDTA caused the oxidation of a stoichiometric amount of iron. At neutral and alkaline pH, EDTA and H2O2 not only oxidizes a stoichiometric amount of iron but also causes the oxidation of the Fe2+ exceeding the concentration of these compounds. In the presence of EDTA, oxidation of Fe2+ in exceeding the concentration of these compounds has a shorter lag phase and an increased rate compared with that in the absence. The solution develops a yellow colour whose intensity is proportional to the amount of Fe2+ exceeding the concentration of these compounds in solution. When the reaction is conducted in the presence of NBT, formazan formation is greatly reduced compared to the control without EDTA and H2O2. The Fe3+-EDTA complex and Fe3+ affected iron oxidation, development of the yellow colour and NBT reduction in a similar fashion. In all these experimental conditions, iron oxidation is greatly reduced in the presence of mannitol, sorbitol and catalase. In phosphate buffer, EDTA oxidized a stoichiometric amount of iron without affecting free Fe2+ oxidation. Fe3+ has no effect on iron oxidation in this buffer.

Fe2+ and other divalent metal ions uncouple Ca2+ transport from (Ca2+-Mg2+)-ATPase in rat liver plasma membranes.

The addition of nanomolar concentrations of free Fe2+, Mn2+, or Co2+ to rat liver plasma membranes resulted in an activation of ATP hydrolysis by these membranes which was not additive with the Ca2+-stimulated ATPase activity coupled to the Ca2+ pump. Detailed analysis showed that, if fact, (i) as for the stimulation of (Ca2+-Mg2+)-ATPase by Ca2+, activation of ATP hydrolysis by Fe2+, Mn3+, or Co2+ followed a cooperative mechanism involving two ions; (ii) two interacting sites for ATP were involved in the activation of both Fe2+- and Ca2+-stimulated ATPase activities; (iii) micromolar concentrations of magnesium caused the same dramatic inhibition of both activities; and (iv) the subcellular distribution of Fe2+-activated ATP hydrolysis activity corresponded to that of plasma membrane markers. This suggests that the (Ca2+-Mg2+)-ATPase might be stimulated not only by Ca2+, but also by Fe2+, Mn2+, or Co2+. However, interaction of (Ca2+-Mg2+)-ATPase with Fe2+, Mn2+, or Co2+ inhibited the Ca2+ pump activity. Furthermore, neither the formation of the phosphorylated intermediate of (Ca2+-Mg2+)-ATPase, nor ATP-dependent (59Fe) uptake could be detected in the presence of Fe2+ concentrations which stimulated ATP hydrolysis. We conclude that: (i) under the influence of certain metal ions, the Ca2+ pump in the liver plasma membrane may be switched to an uncoupled state which displays ATP hydrolysis activity, but does not insure ion transport; (ii) therefore the Ca2+ pump in liver plasma membranes specifically insures Ca2+ transport.

Effects of metal speciation on growth of phytoplankton with special reference to iron

This paper is a compilation of studies concerning the effects of metal speciation on the growth of phytoplankton. Special attention is paid to the speciation and availability of iron in lake Tjeukemeer, The Netherlands. Under laboratory conditions the free ionic metal species generally appear to be most effective in determining metal availability and toxicity. A variety of factors controlling solubility, ion-exchange, complexation or chelation, sorption and electrostatical attraction of metal ions affect the metal speciation, mostly resulting in reduced availabilities. However, some organic metal chelates such as citrates, nitrillotriacetates and the specifically iron chelating siderophores, are sometimes more available than the corresponding free ions. The presence of other metals also influences the availability of a given metal by competing for the same binding sites on the algal cell. This competition leads to antagonism betweene.g. iron nutrition and cadmium toxicity in marine diatoms. In the eutrophic, alkaline, hard and humic lake Tjeukemeer, the free Fe3+ concentration is below measurable levels and does not match the iron requirement of the phytoplankton. So most of the algal iron must have been provided by the predominant inorganic iron colloids and particles bye.g. dissolution or photo-degradation (reduction). If the provision rates of available iron are slow in relation to that of iron uptake, the growth of some phytoplankton species may become iron-limited. Continuous culture work indicated that the iron fraction <0.2 μm from Tjeukemeer,i.e., the ‘soluble’ fraction, is about one third as much available as iron from NH4Fe(SO4)2.12H2O. Different phytoplankton species vary widely in their metal requirements and tolerances. Therefore, metal speciation and availability may affect species composition and succession within phytoplankton communities. So far the assessment of metal availability in natural waters has been complicated by the complex metal chemistry and by methodological limits.

Photosynthetic production of biomass and starch by Chlorella in chemostat culture

AbstractA high temperature strain of Chlorella was grown photosynthetically with nitrogen limitation of growth over a range of dilution rates up to the critical value of 0.22 h−1. The “total cell dry weight” is distinguished from the “real biomass” which is total cell dry weight less starch. Nitrogen‐limited growth of Chlorella, in terms of real biomass, obeyed the simple Monod model of chemostat culture. In a low EDTA medium (about 1 mol of EDTA per mol Fe3+) ferric hydroxide precipitated at pH 7 and caused iron‐limited growth to occur at high dilution rates. Iron precipitation and consequently iron‐limited growth, were prevented by increasing the EDTA to 2 mol per mol Fe3+. It was deduced that Fe3+ was available to the cells only as Fe‐EDTA complex, not as free Fe3+ in the medium. A glycogen‐like starch was stored in the cells and the starch content approached 50% of the total dry weight of cells at low dilution rates. The starch content of the total cell dry weight was practically independent of the growth temperature over the range 28–40°C and the pH over the range 5.5–8.5. The specific rate of starch production (qstarch) reached 0.05 g of starch/g real biomass h.

Requirement of an essential thiol group and ferric iron for the activity of the progesterone-induced porcine uterine purple phosphatase.

The progesterone-induced purple phosphatase isolated from the uterine flushings of pigs is activated by a variety of reagents that cleave disulfide bonds, including 2-mercaptoethanol, dithiothreitol, L-ascorbate, L-cysteine, sulfite, and cyanide. It is inhibited by various mercurials, iodoacetamide, O-iodosobenzoate, and hydrogen peroxide. Thiols increase the specific phosphatase activity from 25 to about 300 units per mg of enzyme. This activation is accompanied by a shift in the extinction maximum to higher energy to yield a protein with a pink coloration. Following maximum activation there is a gradual decrease in enzyme activity and protein color which is accompanied by loss of ferrous iron from the protein. Sodium dithionite at 10 mM or higher causes an immediate inhibition of phosphatase activity and bleaching of color, and can be used to prepare the iron-free apoprotein. The latter can be partially reactivated by Fe3+ salts but not by Fe2+. The Fe3+ restores the pink form of the enzyme with a specific activity of about 200 units/mg of protein. Cu2+ also causes some reactivation, but other metal ions were ineffective. ESR studies showed that the pink form of phosphatase contains approximately 1 atom of high spin ferric iron per molecule. It is concluded that the phosphatase requires a free thiol and Fe3+ for activity. Reduction of the iron leads to complete loss of both color and enzyme activity. The color change from purple to pink represents disulfide reduction and is not due to reduction of iron.

ChemInform Abstract: MODIFICATION OF THE REDOX PROPERTIES OF TETRAPHENYLPORPHYRIN‐COMPLEXES BY BASES IN METHYLENE CHLORIDE SOLUTION, THE EQUILIBRIUM OF DIFFERENT OXIDATION‐STATES WITH ADDED BASE AS MEASURED BY CYCLIC VOLTAMMETRY

Chemischer InformationsdienstVolume 6, Issue 50 Article ChemInform Abstract: MODIFICATION OF THE REDOX PROPERTIES OF TETRAPHENYLPORPHYRIN-COMPLEXES BY BASES IN METHYLENE CHLORIDE SOLUTION, THE EQUILIBRIUM OF DIFFERENT OXIDATION-STATES WITH ADDED BASE AS MEASURED BY CYCLIC VOLTAMMETRY J. MANASSEN, J. MANASSENSearch for more papers by this author J. MANASSEN, J. MANASSENSearch for more papers by this author First published: December 16, 1975 https://doi.org/10.1002/chin.197550094Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume6, Issue50December 16, 1975 RelatedInformation

Kinetics and Equilibrium of Binding of Fe3+ by a Fulvic Acid: A Study by Stopped Flow Methods

The first report of a rate of binding of a metal ion (Fe3+) by a soluble fulvic acid is derived from stopped flow measurements. The rate of complex formation is normal in Wilkins' sense and similar to that for sulfosalicylic acid. Dissociation is slow (t1/2 &gt; 10 s). The binding of Fe3+ by the fulvic acid in acid solution, pH = 1–2.5, was investigated by kinetic analysis in which the reaction of free Fe3+ with sulfosalicylic acid was followed by stopped flow spectrophotometry on a time scale short compared to release of Fe3+ by fulvic acid. Conditional equilibrium constants found were 1.5 ± 0.3 × 104 at pH = 1.5 and 2.5, and 2.8 ± 0.3 × 103 at pH = 1.0 at 25 °C (ionic strength 0.1).

Modification of the Redox‐Properties of Tetraphenylporphyrin‐Complexes by Bases in Methylene‐Chloride Solution. The Equilibrium of Different Oxidation‐States with Added Base as Measured by Cyclic Voltammetry

AbstractThe oxidation half‐wave potentials of Co2+ tetraphenylporphyrin, measured by cyclic voltammetry in methylenechloride solution, are changed by the addition of weak bases like methanol, acetone and dimethylformamide. The wave corresponding to the metal‐oxidation Co2+ ⇄ Co3+ is shifted to lower potential, while the wave, corresponding to the ligand oxidation Co3+(TPP) ⇄ Co3+(TPP)+. is shifted to higher potential. It can be shown, that this is due to a preferential interaction of Co3+(TPP) with the bases, which is stronger than that of the Co2+(TPP) as well as that of the Co3+(TPP)+. Because the shifts are proportional to the concentration of added base, they can be followed quantitatively and the equilibrium constants of the interactions between the different oxidation states and the bases can be calculated. The reduction wave of Co2+(TPP), corresponding to the Co3+ ⇄ Co1+ transition is not changed by the weak bases, but is shifted to lower potential by pyridine and the picolines. The shift is again proportional to the concentration of added base. The reduction wave of Fe3−(TPP)Cl− is not changed by the weak bases, but is shifted to lower potential by pyridine. While the reduction wave of the free Fe3+(TPP)Cl− is irreversible, that of the pyridine‐adduct is reversible. In this case the shift is not proportional to the amount of added base. The voltammetric curves of the Cu, Ni, and Zn tetraphenyl‐porphyrins are not changed by the addition of either the weak or the strong bases.

The Electric Conductance and Structure of the Molten Oxide System PbO-B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

The electric conductivities of the molten oxide system PbO-B2O3-Fe2O3 were determined over the temperature range from liquidus to 1000°C, and the role of ferric ion upon the mechanism of conduction was discussed.The samples containing Fe2O3 0 to 25 mol% were quenched when their conductivities had been measured. Most of the samples formed glass, and the glasses were heat treated to be crystallized. Measurements of Infra-red Spectra and X-ray diffraction were made on the glasses quenched or crystallized to understand the structure of glass in relation to complex borates.The results were as follows.(1) Specific conductivity increases with temperature, and obeys the Arrhenius equation. The values of the apparent activation energies for conduction are about 10 to 20kcal/mol, and are in the same order as in the system PbO-B2O3. Specific conductivities are of the order of 1 ohm-1cm-1 at 1000°C, and increase with the PbO content. From these results, it is considered that the conduction in this system is ionic and electric charge is carried mainly by the Pb2+ ion.(2) The activation energy for conduction depends upon the structure of the complex borate anion, the presence of the ring borate anion giving higher activation energy.(3) The ferric ion has a tendency to form complex anions such as Fe2O54+ in this system, and the concentration of the free Fe3+ ion is small and it contributes little to conduction.(4) The structure of the complex borate anion is related to the formation of the complex ferrite anion.