Showing papers on "Ferric published in 1977"

Analysis and computer simulation of aerobic oxidation of reduced nicotinamide adenine dinucleotide catalyzed by horseradish peroxidase.

Abstract: Under suitable experimental conditions the aerobic oxidation of NADH catalyzed by horseradish peroxidase occurred in four characteristic phases: initial burst, induction phase, steady state, and termination. A trace amount of H2O2 present in the NADH solution brought about initial burst in the formation of oxyperoxidase. About 2 mol of oxyperoxidase was formed per mol of H2O2. When a considerable amount of the ferric enzyme still remained, the initial burst was followed by an induction phase. In this phase the rate of oxyperoxidase formation from the ferric enzyme increased with the decrease of the ferric enzyme and an approximately exponential increase of oxyperoxidase was observed. A rapid oxidation of NADH suddenly began at the end of the induction phase and the oxidation continued at a relatively constant rate. In the steady state, oxygen was consumed and H2O2 accumulated. A drastic terminating reaction suddenly set in when the oxygen concentration decreased under a certain level. During the reaction, H2O2 disappeared accompanying an accelerated oxidation of NADH and the enzyme returned to the ferric form after a transient increase of peroxidase compound II. Time courses of NADH oxidation, O2 consumption, H2O2 accumulation, and formation of enzyme intermediates could be simulated with an electronic computer using 11 elementary reactions and 9 rate equations. The results were also discussed in relation to the mechanism for oscillatory responses of the reaction that appeared in an open system with a continuous supply of oxygen.

Visual estimation of iron in saprolite

Abstract: Secondary iron compounds are the foremost coloring agents in subtropical and tropical saprolites. Amorphous Fe(OH) 3 and goethite are yellow in submicron particles, and coarse goethite is brown. Submicron hematite is red, whereas coarse hematite is gray to black. At most outcrops the color of saprolite is due to the secondary ferric compounds: the hue of the color relates to the mineralogy and particle size of the ferric pigments; value and chroma vary systematically with the proportion of pigment. The color of the saprolite determined by visual comparison with a Munsell Soil Color Chart and referred to our diagram yields a rapid estimate of total iron, as well as ancillary information about particle size and hydration state of the ferric compounds.

Iron transport in Escherichia coli K-12. 2,3-Dihydroxybenzoate-promoted iron uptake.

Abstract: The study of iron uptake promoted by 2,3-dihydroxybenzoate (DHB) into Escherichia coli K-12 aroB mutants allowed some dissection of outer and cytoplasmic membrane functions. These strains are unable to produce the iron-transporting chelate enterochelin, unless fed with a precursor such as DHB. When added to the medium, enterochelin and its natural breakdown products, the linear dimer and trimer of 2,3-dihydroxybenzoylserine (DBS), efficiently transported iron via the feuB, tonB and fep gene products. Thus mutants in these genes were defective in transport of the above chelates. However, feuB and tonB mutants were able to take up iron when DHB was added to the medium. Thus DHB-promoted iron uptake bypassed two functions required for the transport of ferric-enterochelin from the medium. One of these functions, feuB, has been shown to be an outer membrane protein. In contrast to three other iron transport systems including ferric-enterochelin uptake, DHB-promoted iron uptake was little affected by the uncoupler 2,4-dinitrophenol. Dissipation of the energized state of the cytoplasmic membrane apparently only affects those iron transport systems which require an outer membrane protein. Since DHB-promoted iron uptake bypasses the feuB outer membrane protein and the tonB function, it is concluded that, in ferricenterochelin transport, the tonB gene may function in coupling the energized state of the cytoplasmic membrane to the protein-dependent outer membrane permeability. DHB-promoted iron uptake required the synthesis and enzymatic breakdown of enterochelin as judged by the effects of the entF and fesB mutations. A fep mutant was not only deficient in the transport of the ferric chelates of enterochelin and its breakdown products, but was also deficient in DHB-promoted iron uptake. A scheme is presented in which iron diffuses as DHB-complex through the outer membrane, and is subsequently captured by enterochelin or DBS dimer or trimer and translocated across the cytoplasmic membrane.

A kinetic study of the pH-dependent properties of the ferric undecapeptide of cytochrome c (microperoxidase).

Abstract: The ferric form of the haem undecapeptide, derived from horse cytochrome c by peptic digestion, undergoes at least three pH-induced transitions with pK values of 3.4, 5.8 and 7.6. Temperature-jump experiments suggest that the first of these is due to the binding of a deprotonated imidazole group to the feric iron while the second and third arise from the binding of the two available amino groups present (the alpha-NH2 of valine and the epsilon-NH2 of lysine). Molecular models indicate that steric retraints on the peptide dictate that these amino groups may only coordinate to iron atoms via intermolecular bonds, thus leading to the polymerization of the peptide. Cyanide binding studies are in agreement with these conclusions and also yield a value of 3.6 X 10(6) M-1 s-1 for the intrinsic combination constant of CN- anion with the haem. A model is proposed which describes the pH-dependent properties of the ferric undecapeptide.

Investigations into Black Extrinsic Tooth Stain

Abstract: An investigation has been carried out into the nature of the black pigment in black extrinsic tooth stain. The results suggest that the black material is a ferric salt, probably ferric sulfide, formed by the reaction between hydrogen sulfide produced by bacterial action and iron in the saliva or gingival exudate.

On the mechanism of action of soybean lipoxygenase-1. A stopped-flow kinetic study of the formation and conversion of yellow and purple enzyme species

Abstract: 1 The conversion of the native iron-containing lipoxygenase-1 into yellow and purple ferric enzyme species by 13-L-hydroperoxy-9-cis, 11-trans-octadecadienoic acid (R-13-OOH) was studied by measuring the absorbance changes at 330 nm and 580 nm, respectively in the stopped-flow apparatus. The pseudo-first-order rate constant for this reaction was found to be 50 s−1 at 4.4°C, either in the presence or absence of O2. This rate constant is lower than the one for R-13-OOH formation from linoleic acid and O2 catalysed by lipoxygenase-1: kcat= 232 s−1 at 4.4°C. 2 The coloured ferric enzymes are formed only in the presence of R-13-OOH; therefore the formation of the coloured ferric enzymes from oxygen, linoleic acid and the native enzyme indicates that the latter is active even before it is converted into the ferric forms. 3 Under anaerobic conditions the yellow and purple enzyme species are rapidly converted into colourless ferrous enzyme species by linoleic acid at a rate which is faster than the formation of the coloured enzymes from R-13-OOH and the native ferrous enzyme. 4 Both the aerobic formation of the coloured ferric enzymes and the anaerobic bleaching of these enzymes occur more slowly when [11-2H2]linoleic acid instead of unlabeled linoleic acid is used. The kinetic deuterium isotope effect as estimated from the rates of aerobic formation of R-13-OOH is approximately 9, whereas in the anaerobic conversion of R-13-OOH and deuterated linoleic acid a value of 1.1 is found. This demonstrates that H abstraction from linoleic acid determines the rate of the aerobic formation but not of the anaerobic conversion of R-13-OOH. 5 The rate constant for the anaerobic conversion of [11-2H2]linoleic acid by the yellow ferric enzyme species, k(2H) = 30 s−1 at 25°C, is close to the rate constant for the overall oxygenation reaction of the deuterated substrate, kcat(2H) = 32 s−1. For unlabelled linoleic acid the rate constants of the anaerobic H-abstraction step and the overall oxygenation reaction were found to be 111 s-1 and 290 s−1, respectively at 25°C. The former rate constant is probably affected by substrate inhibition. 6 Since the native ferrous enzyme is capable of catalysing H abstraction from linoleic acid under aerobic but not under anaerobic conditions, while the yellow ferric enzyme is active either in the absence or presence of O2, it is proposed that O2 reversibly converts the ferrous enzyme species into a ferric state.

Electron-paramagnetic-resonance studies of leghaemoglobins from soya-bean and cowpea root nodules. Identification of nitrosyl-leghaemoglobin in crude leghaemoglobin preparations.

Abstract: 1. Leghaemoglobins from soya-bean (Glycine max) and cowpea (Vigna unguiculata) root nodules were purified by chromatography on DEAE-cellulose phosphate columns at pH8.0 and pH5.8, to avoid the relatively low pH (5.2) commonly used to purify these proteins. 2. E.p.r. (electron-paramagnetic-resonance) spectra of the fluoride, azide, hydroxide and cyanide complexes of these ferric leghaemoglobins were very similar to the spectra of the corresponding myoglobin derivatives, indicating that the immediate environment of the iron in leghaemoglobin and myoglobin is similar, an imidazole moiety of histidine being the proximal ligand to the haem iron [cf. Appleby, Blumberg, Peisach, Wittenberg & Wittenberg (1976) J. Biol. Chem. 251, 6090–6096]. 3. E.p.r. spectra of the acid-metleghaemoglobins showed prominent high-spin features very near g=6 and g=2 and, unlike myoglobin, small low-spin absorptions near g=2.26, 2.72 and 3.14. The width of the g=6 absorption derivative at 10–20K was about 4–4.5mT, similar to the value for acid-methaemoglobin. In contrast, a recently published (Appleby et al., 1976) spectrum of acid-metleghaemoglobin a had less high-spin character and a much broader absorption derivative around g=6. 4. E.p.r. spectra of ferric leghaemoglobin nicotinate and imidazole complexes suggest that the low-spin absorption near g=3.14 can be attributed to a trace of ferric leghaemoglobin nicotinate, and those near g=2.26 and 2.72 are from an endogenous dihistidyl haemichrome. 5. A large e.p.r. signal at g=2 in all samples of crude leghaemoglobin was shown to be from nitrosyl-leghaemoglobin. A soya-bean sample contained 27±3% of the latter. A previously unidentified form of soya-bean ferrous leghaemoglobin a was shown to be its nitrosyl derivative. If this is not an artifact, and occurs in the root nodule, the nitrosyl radical may interfere with the function of leghaemoglobin.

Interaction of monomeric and polymeric species of metal ions with clay surfaces. I. Adsorption of iron(III) species

Abstract: Uitrafiltration or dialysis against distilled water was used to separate polymerized ferric hydroxy cations from the monomeric cations in hydrolysed solutions of ferric nitrate. Separated poly[Fe(III)-OH] cations were polydispersed and the positive charge was inversely related to molecular size. The separated poly[Fe(III)-OH] cations were found to be stable and did not condense further during a period of 6 months. The association of iron(III) with the surfaces of sodium-kaolinite, sodium-bentonite and sodiumillite was studied using hydrolysed ferric nitrate solutions and separated poly[Fe(III)-OH] cations. As the OH/Fe ratio (and pH) of the ferric nitrate solutions increased, the critical coagulation concentration (CCC) and the maximum adsorption of iron(III) increased. The amount of iron adsorbed in the form of separated po1y[Fe(III)-OH] cations was small and was related to the positive charge per iron atom of the polycations. It is proposed that iron(III) in solutions containing only polycations and solutions containing a mixture of mono- and polycations reacted differently with clay surfaces. A reaction of polycations with the surface hydroxyls leading to chemisorption and irreversible flocculation of clays is proposed.

Catalytic removal of hydrogen sulfide from gases

Abstract: In a catalytic oxidation-reduction process of removing hydrogen sulfide gas from a gaseous fluid stream, the improved step of contacting a gaseous stream containing hydrogen sulfide gas with an aqueous solution containing iron chelate catalyst having iron in the ferric state wherein the iron chelate catalyst comprises at least two iron chelating agents with at least one of said agents being an amine compound selected from the group consisting of polyamino polycarboxylic acids, polyamino alkyl polycarboxylic acids, polyamino hydroxyalkyl polycarboxylic acids, and poly(phosphonoalkyl) amines, and their alkali metal salts and another of said iron chelating agents being selected from the group of polyhydroxy compounds consisting of monosaccharides, disaccharides, reduced monosaccharides, reduced disaccharides, monosaccharide acids, disaccharide acids, and their alkali metal salts; and said solution having a pH ranging between about pH 5.5 and about pH 13.

The influence of phosphorus, zinc and manganese on absorption and translocation of iron in watercress

Abstract: Absorption and translocation of iron by intact watercress plants (Rorippa nasturtium-aquaticum (L) Hayek) was studied in short period uptake experiments utilising 59Fe labelled ferric chloride. Total translocation of iron was inhibited by increasing levels of phosphorus, zinc and manganese in the nutrient medium; the elevated phosphorus and zinc concentrations enhanced iron absorption into roots, but increased retention of absorbed iron in translocating portions of the plant. High levels of manganese in the medium reduced the initial absorption of iron into the root system.

Thermal and Mössbauer Studies of Iron‐Containing Hydrous Silicates.

Abstract: When heated in air, minnesotaite begins to oxidise to a ferric form aI 400°C. By the onset ofdehydroxylation at 600°C, oxidation is virtually complete without significant changes in the lattice parameters.

Anion and solvent effects on the rate of reduction of triplet excited thiazine dyes by ferrous ions

Abstract: — The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.

Interaction of monomeric and polymeric species of metal ions with clay surfaces. II. Changes in surface properties of clays after addition of iron(III)

Abstract: The adsorption of poly [Fe(III)-OH] cation by claysurfaces led to flocculation of clay particles possibly by polymer bridging while the addition of iron(III) from hydrolysed ferric nitrate solutions resulted in flocculation and cementation by precipitated iron(III). Electrokinetically clays with adsorbed iron(III) behaved similarly to amorphous ferric hydroxides with positive mobilities below the point of zero charge (PZC). Polycations reversed the charge on the clay particles at maximum adsorption, which probably represents neutralization of charge due to surface hydroxyls. When hydrolysed ferric nitrate solutions were added to kaolinite and illite charge reversal occurred at pH values below 6. Adsorption of iron(III) resulted in a partial reduction of negative charge in clays. The reduction of negative charge in kaolinite and illite was close to the charge due to surface hydroxyls. The net charge estimated at all pH values corresponded with the electrophoretic mobility in all the iron(III) clay complexes except bentonite with adsorbed polycations.