Formation of super-reduced Chromatium high-potential iron--sulphur protein in aqueous solution by pulse radiolysis.
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ABSTRACT:
SUBMITTER: Butler J
PROVIDER: S-EPMC1162045 | biostudies-other | 1980 Sep
REPOSITORIES: biostudies-other
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Project description:Mössbauer-effect studies of the super-reduced form of Chromatium high-potential iron-sulphur protein indicate that the iron atoms are in a similar valency state to those in reduced ferredoxin from Clostridium pasteurianum, with possibly some inequivalence between the iron atoms within the four-iron centre. Mössbauer spectroscopy also shows magnetic differences between the four-iron centres in the two proteins.
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Project description:The interaction of e-aq., CO2-. and one-electron reduced nitroaromatics (RNO2-.) with ascorbate oxidase (AAO) was studied in aqueous solution at pH 6.0 and 7.5 by using the technique of pulse radiolysis. From observations at 330, 410 and 610 nm, interaction of e-aq. and CO2-. with AAO results in non-specific reduction of the protein followed by reduction of Type 1 Cu in a rate-determining intramolecular step. Only a few per cent of the reducing equivalents ultimately results in reduction of Type 1 Cu. With large excesses of reducing equivalents (e-aq. and CO2-.) with respect to the copper concentration, the amount of Type 1 copper reduced never exceeds 50% of the total amount of Type 1 copper after a single radiation pulse. With less-powerful reducing agents, e.g. RNO2-. reduction of Type 1 Cu occurs via a bimolecular step, and there is no evidence for formation of radicals on protein residues. From observations at 330 nm it is evident that Type 2 and/or Type 3 Cu may also be reduced along with Type 1 Cu. Almost stoichiometric reduction of AAO by RNO2-. was observed, e.g. the protein accepts 6-7 reducing equivalents. It is inferred that the various types of redox couples Cu2+/Cu+ are in equilibrium and that intramolecular electron transfer between the different types of Cu is not rate-determining when using RNO2-. as reducing agent.
| S-EPMC1154068 | biostudies-other
Project description:In this study, steady-state and time-resolved radiolysis methods were used to determine the primary reaction pathways and kinetic parameters for the reactions of hydroxyl radical with microcystin-LR (MC-LR). The fundamental kinetic data is critical for the accurate evaluation of hydroxyl-radical based technologies for the destruction of this problematic class of cyanotoxins. The bimolecular rate constant for the reaction of hydroxyl radical with MC-LR is 2.3 (+/-0.1) x 10(10) M(-1)s(-1) based on time-resolved competition kinetics with SCN-at low conversions using pulsed radiolysis experiments. The reaction of hydroxyl radical with MC-LR can occur via a number of competing reaction pathways, including addition to the benzene ring and diene and abstraction of aliphatic hydrogen atoms. LC-MS analyses indicate the major products from the reaction of hydroxyl radicals with MC-LR involve addition of hydroxyl radical to the benzene ring and diene moieties of the Adda side chain. Transient absorption spectroscopy monitored between 260-500 nm, following pulsed hydroxyl radical generation, indicate the formation of a transient species with absorption maxima at 270 and 310 nm. The absorption maxima and lifetime of the transient species are characteristic of hydroxycyclohexadienyl radicals resulting from the addition of hydroxyl radical to the benzene ring. The rate constant for the formation of hydroxycyclohexadienyl radical is 1.0 (+/-0.1) x 10(10) M(-1)s(-1) accounting for approximately 40% of the primary reaction pathways. Representative rate constants and partitioning of hydroxyl radical reactions were assessed based on the reactivities of surrogate substrates and individual amino acids. Summation of the individual reactivities of hydroxyl radical at the different reactive sites (amino acids) leads to a rate constant of 2.1 x 10(10) M(-1) s(-1) in good agreementwith the rate constant determined in our studies. The relative magnitude of the rate constants for the reactions of hydroxyl radical with the individual amino acids and appropriate surrogates, suggest 60-70% reactions of hydroxyl radical occur at the benzene and diene functional groups of the Adda moiety.
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Project description:Reduction of fully oxidized Clostridium pasteurianum 8-Feox.,ox. ferredoxin by using pulse-radiolysis techniques yields the half-reduced species 8-Feox.,red. ferredoxin. The subsequent oxidation of 8-Feox.,red. ferredoxin with Co(NH3)5Cl2+ was studied. From a comparison with stopped-flow studies on the 2:1 Co(NH3)5Cl2+ oxidation of 8-Fered.,red. ferredoxin to the 8-Feox.,ox. form it is concluded that there is no redox co-operativity between the two 4-Fe centres in these reactions.
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Project description:By using the technique of pulse radiolysis to generate O2-., it is demonstrated that Co(II) derivatives of bovine superoxide dismutase in which the copper alone and both the copper and zinc of the enzyme have been substituted by Co(II), resulting in (Co,Zn)- and (Co,Co)-proteins, are capable of catalytically dismutating O2-. with 'turnover' rate constants of 4.8 X 10(6) dm3.s-1.mol-1 and 3.1 X 10(6) dm3.s-1.mol-1 respectively. The activities of the proteins are independent of the pH (7.4-9.4) and are about three orders of magnitude less than that of the native (Cu,Zn)-protein. The rate constants for the initial interaction of O2-. with the Co-proteins were determined to be (1.5-1.6) X 10(9) dm3.s-1.mol-1; however, in the presence of phosphate, partial inhibition is apparent [k approximately (1.9-2.3) X 10(8) dm3.s-1.mol-1]. To account for the experimental observations, two reaction schemes are presented, involving initially either complex-formation or redox reactions between O2-. and Co(II). This is the first demonstration that substitution of a metal into the vacant copper site of (Cu,Zn)-protein results in proteins that retain superoxide dismutase activity.
| S-EPMC1158461 | biostudies-other
Project description:1. The previous Mössbauer work on Chromatium high-potential iron-sulphur protein by Moss et al. (1968) and Evans et al. (1970) was extended to high applied magnetic fields. 2. Measurements of the reduced protein confirm that it is non-magnetic. 3. Spectra of the oxidized protein in applied magnetic fields clearly indicate that some iron atoms have a positive hyperfine field, which is evidence for antiferromagnetic coupling. 4. The spectra can be interpreted in terms of two types of iron atom with positive and negative hyperfine fields of 9 and 12T respectively. 5. A consideration of the chemical shifts and other evidence suggests formal valences of two Fe(3+) and two Fe(2+) atoms in the non-magnetic reduced state, and three Fe(3+) atoms and one Fe(2+) atom in the oxidized state. 6. However, no separate Fe(3+) and Fe(2+) spectra are seen, suggesting that the d electrons are not localized on particular iron atoms.
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Project description:Antimony (Sb) is increasingly being recognized as an important contaminant due to its various industrial applications and mining operations. Environmental remediation approaches for Sb are still lacking, as is the understanding of Sb environmental chemistry. In this study, biosolid biochar (BSBC) was produced and utilized to remove antimonate (Sb(V)) from aqueous solution. Zirconium (Zr), Zirconium-iron (Zr-Fe) and Fe-O coated BSBC were synthesized for enhancing Sb(V) sorption capacities of BSBC. The combined results of specific surface area, FTIR, SEM-EDS, TEM-EDS, and XPS confirmed that Zr and/or Zr-Fe were successfully coated onto BSBC. The effects of reaction time, pH, initial Sb(V) concentration, adsorbate doses, ionic strength, temperature, and the influence of major competitive co-existing anions and cations on the adsorption of Sb(V) were investigated. The maximum sorption capacity of Zr-O, Zr-Fe, Zr-FeCl3, Fe-O, and FeCl3 coated BSBC were 66.67, 98.04, 85.47, 39.68, and 31.54 mg/g respectively under acidic conditions. The XPS results revealed redox transformation of Sb(V) species to Sb(III) occurred under oxic conditions, demonstrating the biochar's ability to behave as an electron shuttle during sorption. The sorption study suggests that Zr-O and Zr-O-Fe coated BSBC could perform as favourable adsorbents for mitigating Sb(V) contaminated waters.
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Project description:Aqueous solutions of Lu3+- perchlorate, triflate and chloride were measured by Raman spectroscopy. A weak, isotropic mode at 396 cm-1 (full width at half height (fwhh) at 50 cm-1) was observed in perchlorate and triflate solutions. This mode was assigned to the totally symmetric stretching mode of [Lu(OH?)?]3+, ??LuO?. In Lu(ClO?)? solutions in heavy water, the ??LuO? symmetric stretch of [Lu(OD?)?]3+ appears at 376.5 cm-1. The shift confirms the theoretical isotopic effect of this mode. In the anisotropic scattering of aqueous Lu(ClO?)?, five bands of very low intensity were observed at 113 cm-1, 161.6 cm-1, 231 cm-1, 261.3 cm-1 and 344 cm-1. In LuCl? (aq) solutions measured over a concentration range from 0.105?3.199 mol·L-1 a 1:1 chloro-complex was detected. Its equilibrium concentration, however, disappeared rapidly with dilution and vanished at a concentration < 0.5 mol·L-1. Quantitative Raman spectroscopy allowed the detection of the fractions of [Lu(OH?)?]3+, the fully hydrated species and the mono-chloro complex, [Lu(OH?)?Cl]2+. In a ternary LuCl?/HCl solution, a mixtrure of chloro-complex species of the type [Lu(OH?)8-nCln]+3-n (n = 1 and 2) were detected. DFT geometry optimization and frequency calculations are reported for Lu3+- water cluster in vacuo and with a polarizable dielectric continuum (PC) model including the bulk solvent implicitly. The bond distance and angle for [Lu(OH?)?]3+ within the PC are in good agreement with data from structural experiments. The DFT frequencies for the Lu-O modes of [Lu(OH?)?]3+ and its deuterated analog [Lu(OD?)?]3+ in a PC are in fair agreement with the experimental ones. The calculated hydration enthalpy of Lu3+ (aq) is slightly lower than the experimental value.
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Project description:The lead(II) complexes formed with the multidentate chelator L-cysteine (H2Cys) in an alkaline aqueous solution were studied using (207)Pb, (13)C, and (1)H NMR, Pb LIII-edge X-ray absorption, and UV-vis spectroscopic techniques, complemented by electrospray ion mass spectrometry (ESI-MS). The H2Cys/Pb(II) mole ratios were varied from 2.1 to 10.0 for two sets of solutions with CPb(II) = 0.01 and 0.1 M, respectively, prepared at pH values (9.1-10.4) for which precipitates of lead(II) cysteine dissolved. At low H2Cys/Pb(II) mole ratios (2.1-3.0), a mixture of the dithiolate [Pb(S,N-Cys)2](2-) and [Pb(S,N,O-Cys)(S-HCys)](-) complexes with average Pb-(N/O) and Pb-S distances of 2.42 ± 0.04 and 2.64 ± 0.04 Å, respectively, was found to dominate. At high concentration of free cysteinate (>0.7 M), a significant amount converts to the trithiolate [Pb(S,N-Cys)(S-HCys)2](2-), including a minor amount of a PbS3-coordinated [Pb(S-HCys)3](-) complex. The coordination mode was evaluated by fitting linear combinations of EXAFS oscillations to the experimental spectra and by examining the (207)Pb NMR signals in the chemical shift range ?Pb = 2006-2507 ppm, which became increasingly deshielded with increasing free cysteinate concentration. One-pulse magic-angle-spinning (MAS) (207)Pb NMR spectra of crystalline Pb(aet)2 (Haet = 2-aminoethanethiol or cysteamine) with PbS2N2 coordination were measured for comparison (?iso = 2105 ppm). The UV-vis spectra displayed absorption maxima at 298-300 nm (S(-) ? Pb(II) charge transfer) for the dithiolate PbS2N(N/O) species; with increasing ligand excess, a shoulder appeared at ?330 nm for the trithiolate PbS3N and PbS3 (minor) complexes. The results provide spectroscopic fingerprints for structural models for lead(II) coordination modes to proteins and enzymes.
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Project description:O?.- scavenger: The rate constant for the rapid reaction of the ROS superoxide with the reduced vitamin B?? radical complex cob(II)alamin was directly determined to be 3.8×10(8) M?¹ s?¹. This rate was independent of pH over the range 5.5-8.7. These results have implications for studying the use of B?? supplements to combat diseases associated with oxidative stress.
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