SEARCH · Search PubMed

Results for “Redox potential”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources

PubMed1999

Modeling continuous bioleach reactors

The results of recent research have shown that the bioleaching of sulfide minerals occurs via a two-step mechanism. In this mechanism, the sulfide mineral is chemically oxidized by the ferric-iron in the bioleaching liquor. The ferrous-iron produced is subsequently oxidized to ferric-iron by the microorganism. Further research has shown that the rates of both the ferric leaching and ferrous-iron oxidation are governed by the ferric/ferrous-iron ratio (i.e., the redox potential). During the steady-state operation of a bioleach reactor, the rate of iron turnover between the chemical ferric leaching of the mineral and the bacterial oxidation of the ferrous-iron will define the rate and the redox potential at which the system will operate. The balance between the two rates will in turn depend on the species used, the microbial concentration, the residence time employed, the nature of the sulfide mineral being leached, and its active surface area. The model described proposes that the residence time and microbial species present determine the microbial growth rate, which in turn determines the redox potential in the bioleach liquor. The redox potential of the solution, in turn, determines the degree of leaching of the mineral; that is, conversion in the bioleach reactor. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗

PubMed1997

Oxidation of phenolic compounds by lactoperoxidase. Evidence for the presence of a low-potential compound II during catalytic turnover.

The lactoperoxidase (LPO)-catalyzed oxidation of p-phenols by hydrogen peroxide has been studied. The behavior of the enzyme differs from that of other peroxidases in this reaction. In particular LPO shows several catalytic intermediates during the catalytic cycle because of its capability to delocalize an oxidizing equivalent on a protein amino acid residue. In the phenol oxidation the enzyme Compound I species, containing an iron-oxo and a protein radical, uses the iron-oxo group at acidic pH and the protein radical in neutral or basic medium. Kinetic and spectroscopic studies indicate that the ionization state of an amino acid residue with pKa 5.8 +/- 0.2, probably the distal histidine, controls the enzyme intermediate forms at different pH. LPO undergoes inactivation during the oxidation of phenols. The inactivation is reversible and depends on the easy formation of Compound III even at low oxidant concentration. The inactivation is due to the substrate redox potential since the best substrate is that with lowest redox potential, while the worst substrate has the highest potential. This strongly indicates that Compound II, formed during catalytic turnover, has a low redox potential, making easier its oxidation by hydrogen peroxide to Compound III. The dependence of LPO activity on the phenols redox potential suggests that the protein radical where an oxidizing equivalent can be localized is a tyrosyl residue.

Catalysis↗

PubMed1997

Redox dependence for photoligation of manganese to the apo-water-oxidizing complex in chloroplasts and photosystem II membranes.

Effects of reducing reagents and redox potentials on photoactivation were studied in Mn-depleted chloroplasts and PSII membranes. Exogenous reducing reagents abolished photoactivation in PSII membranes, while they stimulated photoactivation in chloroplasts. To determine how reducing reagents can have such opposing effects in these preparations, we studied how redox potentials affect photoactivation in the range from 0 mV to +500 mV. In chloroplasts, a modest yield of photoactivation was obtained in the redox potential range of +100 and +330 mV at pH 7.5. The yield of photoactivation decreased at redox potentials above +330 mV, and drastically increased below potentials of +100 mV. Nernst plots of the data show that an n = 1 redox component with an Em7.5 of +374 mV, as well as an n = 2 redox component with an Em7.5 of +61 mV, is involved in photoactivation of chloroplasts isolated from dark-grown spruce seedlings. In the case of PSII membranes, photoactivation decreased sharply on either side of +335 mV at pH 5.5. The n = 1 redox components with Em5.5 of +375 and +319 mV may be involved, both of which showed pH dependences of -60 mV/pH unit. DCMU abolished photoactivation in chloroplasts, but did not affect the dependence of photoactivation on oxidation-reduction potentials in PSII membranes. The component with an Em5.5 of +319 mV involved in photoactivation of PSII membranes was also observed in the dependence of Mn solubilization on oxidation-reduction potentials with PSII membranes lacking extrinsic proteins, suggesting that the reduction of Mn with higher valences to Mn(II) by exogenous reducing reagents reversibly occurs in the intermediates or an active center during photoactivation in PSII membranes. Involvement of such redox components in photoactivation in chloroplasts and PSII membranes is discussed.

Chloroplasts↗

PubMed2005

Structure and redox properties of the haem centre in the C357M mutant of cytochrome P450cam.

The effects of site-specific mutation of the axial cysteine (C357M) to a methionine residue in cytochrome P450cam on the enzyme's coordination geometry and redox potential have been investigated. The absorption spectra of the haem centre in the C357M mutant of the enzyme showed close similarity to those of cytochrome c both in the oxidised and reduced forms. A well-defined absorption peak at 695 nm, similar to that seen in the case of cytochrome c and characteristic of methionine ligation to the ferric haem, was observed. The results indicated that the haem of C357M cytochrome P450cam is possibly axially coordinated to a methionine and a histidine, analogously to cytochrome c. The circular dichroism spectra in the visible and the far-UV regions suggested that the tertiary structure of the haem cavity in the C357M mutant cytochrome P450cam was distinctly different from that in the wild-type enzyme or in cytochrome c, although the secondary structure of the mutant remained identical to that of the wild-type cytochrome P450cam. Comparison of the natures of the CD spectra in the 400 nm and 695 nm regions of the C357M mutant of cytochrome P450cam with those of horse cytochrome c suggested (R) chirality at the sulfur atom of the iron-bound methionine residue in the mutant. The redox potential of the haem centre, estimated by redox titration of the C357M mutant, was found to be +260 mV, which is much higher than that in the wild-type enzyme and similar to the redox potential of cytochrome c. This supported the concept that axial ligation of the haem plays the major role in tuning the redox potential of the haem centre in haem proteins.

Amino Acid Sequence↗

PubMed1986

Correlations between redox-state potential changes in different tissues and the heart frequency in vivo.

Redosis evoked in different tissues by methylene-blue or menadione (oxidants), resulted in an increase in heart frequency, while oxidosis evoked by thiamine or cysteine (reductants) diminished the frequency. In isolated organ tissues where compensatory redox feed back overshoots are rarely to develop, owing to the low redox buffer capacity and lack of the influence of nervous and humoral factors, the heart frequency decreased in response to direct oxidosis induced by the application of oxidants, and increased following reductant application; this suggested an environmental type redox regulatory influence of the agents rather than specific action of the agents. This environmental type effect can result from direct action on isolated organs, or from direct and indirect actions in vivo. An increased redox-state potential resulted in decreased heart frequency and inversely. In a pathological situation provoked by complete strangulation of aortae, a significant oxidosis developed in parallel with a decrease in heart frequency. On increasing the redox buffer capacity by application of methylene-blue (oxidant), or thiamine (reductant) both the redox and the resulting heart frequency changes could readily be counteracted. When cigarette smoke was pumped through an intratracheal tube, a significant redosis developed in the heart ventricle in parallel with an increased heart frequency. These data show that regardless of the origin of redox-state potential changes in tissues, a shift to oxidosis decreases and a shift to redosis increases the heart frequency.

Animals↗

PubMed2001

Coupled molecular switches: a redox-responsive ligand and the redox-switched complexation of metal ions.

1,1'-(OC2H4OTos)2-ferrocene was treated with various diaza-[n]-crown-m (n/m = 12/4, 15/5, 18/6) to give three ferrocene cryptands (n/m = 12/4 (FcCrypt), 15/5, 18/6). The complexation of Group 1 and 2 metal ions by FcCrypt leads to large shifts in the redox potentials (up to +500 mV relative to FcCrypt) and consequently to a drastic decrease in the binding strength (up to 10(8)) in the ferrocene cryptands. The redox potential of Fcpda (1,1'-N,N'-bis-(dipicol-2-ylamino)-3.3',4,4'-tetraphenylferrocene) can be modified reversibly by complexation of Zn2 (E(Fcdpa) = -0.13 V, E(Fcdpa-2Zn+) = +0.66 V and E(Fcdpa-Zn2+) = +0.72 V). The X-ray crystal structure of FcCrypt-Ca-(ClO4)2 . H2O was determined; Ca2+ is coordinated by six oxygen (Ca2+-O 238.7, 239.1, 239.5, 242.6, 243.6, 247.7 pm) and two nitrogen donors (Ca2+-N 256.1, 259.2 pm) and displays a short Fe-Ca2+ contact (402.7 pm). The stability constants of FcCrypt-Na+ (IgK=8.32 in CH3CN) and FcCrypt-K+ (IgK = 4.54 in CH3CN) were determined. The precise adjustment of complex stability and redox potentials of Fcdpa, Fcdpa-Zn2+, FcCrypt (+0.12 V), and FcCrypt-Na+ (+0.395 V) allows coupling of the redox-switchable ferrocene cryptand and the redox-responsive aminoferrocene. In a cyclic process starting from a mixture of Fcdpa+PF6- and FcCrypt-Na+ the addition of Zn(CF3SO3)2 raises the redox potential of Fcdpa+ to that of Fcdpa+-Zn2+. This complex oxidizes FcCrypt-Na+, while the oxidized crypt- and displays a drastically reduced affinity towards Na+, so that a mixture containing FcCrypt+, Fcdpa-Zn2+, and uncoordinated Na+ results. The alkali metal ion is recomplexed after cyclam-assisted removal of Zn2+ from the Fcdpa-Zn2+ complex, since Fcdpa is oxidized by FcCrypt+ with reformation of FcCrypt-Na+. Thus two independent chemical processes--the complexation/ decomplexation of Zn2+ and of Na+--are linked indirectly with mediation by electron-transfer reactions.

Journal Article↗

PubMed2004

Plant biomass and species composition along an environmental gradient in montane riparian meadows.

In riparian meadows, narrow zonation of the dominant vegetation frequently occurs along the elevational gradient from the stream edge to the floodplain terrace. We measured plant species composition and above- and belowground biomass in three riparian plant communities-a priori defined as wet, moist, and dry meadow-along short streamside topographic gradients in two montane meadows in northeast Oregon. The objectives were to: (1). compare above- and belowground biomass in the three meadow communities; (2). examine relations among plant species richness, biomass distribution, water table depth, and soil redox potential along the streamside elevational gradients. We installed wells and platinum electrodes along transects (perpendicular to the stream; n=5 per site) through the three plant communities, and monitored water table depth and soil redox potential (10 and 25 cm depth) from July 1997 to August 1999. Mean water table depth and soil redox potential differed significantly along the transects, and characterized a strong environmental gradient. Community differences in plant species composition were reflected in biomass distribution. Highest total biomass (live+dead) occurred in the sedge-dominated wet meadows (4311+/-289 g/m(2)), intermediate biomass (2236+/-221 g/m(2)) was seen in the moist meadow communities, dominated by grasses and sedges, and lowest biomass (1403+/-113 g/m(2)) was observed in the more diverse dry meadows, dominated by grasses and forbs. In the wet and moist communities, belowground biomass (live+dead) comprised 68-81% of the totals. Rhizome-to-root ratios and distinctive vertical profiles of belowground biomass reflected characteristics of the dominant graminoid species within each community. Total biomass was positively correlated with mean water table depth, and negatively correlated with mean redox potential (10 cm and 25 cm depths; P <0.01) and species richness ( P <0.05), indicating that the distribution of biomass coincided with the streamside edaphic gradient in these riparian meadows.

Altitude↗

PubMed2000

Self-assembly of heme A and heme B in a designed four-helix bundle: implications for a cytochrome c oxidase maquette.

Heme A, a prosthetic group of cytochrome c oxidase [EC 1.9.3.1], has been introduced into two de novo designed four helix bundle proteins, [H10A24](2) and [H10H24](2), known to bind 2-4 equiv of heme B, respectively [Robertson, D. E., Farid, R. S., Moser, C. C., Mulholland, S. E., Pidikiti, R., Lear, J. D., Wand, A., J., DeGrado, W. F., and Dutton, P. L. (1994) Nature 368, 425-432]. [H10A24](2), [Ac-CGGGELWKL x HEELLKK x FEELLKL x AEERLKK x L-CONH(2)](2)(2), binds two heme A molecules per four-helix unit via bis-histidine ligation at the 10,10' positions with measured K(d) values of <0.1 and 5 nM, values much lower than those measured for heme B (K(d) values of 50 and 800 nM). The heme A-protein complex, [heme A-H10A24](2), exhibits well-defined absorption spectra in both the ferric and ferrous states, and an electron paramagnetic resonance spectrum characteristic of a low spin heme in the ferric form. A single midpoint redox potential (E(m8)) was determined for [heme A-H10A24](2) at -45 mV (vs SHE), which is significantly higher than that of the protein bound heme B (-130 and -200 mV). The observation of a single midpoint redox potential for [heme A-H10A24](2) and a pair of midpoints for [heme B-H10A24](2) indicates that the di-alpha-helical monomers are oriented in an anti topology (disulfides on opposite sides of bundle) in the former (lacking heme-heme electrostatic interaction) and syn in the latter. A mixture of global topologies was indicated by the potentiometric titration of the related [heme A-H10H24](2) which possess two distinct reduction potentials of +41 (31%) and -65 mV (69%). Self-assembly of the mixed cofactor heme A-heme B-[H10A24](2) was accomplished by addition of a single equivalent of each heme A and heme B to [H10A24](2). The single midpoint redox potential of heme B, E(m8) = -200 mV, together with the split midpoint redox potential of heme A in heme A-heme B-[H10A24](2), E(m8) = +28 mV (33%) and -65 mV (67%), indicated the existence of both syn and anti topologies of the two di-alpha-helical monomers in this four helix bundle. Synthesis of the mixed cofactor [heme A-heme B-H10H24](2) was accomplished by addition of a 2 equiv of each heme A and heme B to [H10H24](2) and potentiometry indicated the pair of hemes B resided in the 10,10' sites and heme A occupied the 24,24' sites. The results indicate that heme peripheral structure controls the orientation of the di-alpha-helical monomers in the four-helix bundle which are interchangeable between syn and anti topologies. In the reduced form, [heme A-H10A24](2), reacts quantitatively to form [carbonmonoxy-heme A-H10A24](2) as evidenced by optical spectroscopy. The synthetic [heme A-H10A24](2) can be enzymatically reduced by NAD(P)H with natural reductases under anaerobic conditions, and reversibly oxidized by dioxygen to the ferric form.

Animals↗

PubMed2004

Electrostatic interaction between redox cofactors in photosynthetic reaction centers.

Intramolecular electron transfer within proteins is an essential process in bioenergetics. Redox cofactors are embedded in proteins, and this matrix strongly influences their redox potential. Several cofactors are usually found in these complexes, and they are structurally organized in a chain with distances between the electron donor and acceptor short enough to allow rapid electron tunneling. Among the different interactions that contribute to the determination of the redox potential of these cofactors, electrostatic interactions are important but restive to direct experimental characterization. The influence of interaction between cofactors is evidenced here experimentally by means of redox titrations and time-resolved spectroscopy in a chimeric bacterial reaction center (Maki, H., Matsuura, K., Shimada, K., and Nagashima, K. V. P. (2003) J. Biol. Chem. 278, 3921-3928) composed of the core subunits of Rubrivivax gelatinosus and the tetraheme cytochrome of Blastochloris viridis. The absorption spectra and orientations of the various cofactors of this chimeric reaction center are similar to those found in their respective native protein, indicating that their local environment is conserved. However, the redox potentials of both the primary electron donor and its closest heme are changed. The redox potential of the primary electron donor is downshifted in the chimeric reaction center when compared with the wild type, whereas, conversely, that of its closet heme is upshifted. We propose a model in which these reciprocal shifts in the midpoint potentials of two electron transfer partners are explained by an electrostatic interaction between them.

Coenzymes↗

PubMed2000

Transmembrane redox sensor of ryanodine receptor complex.

Inositol 1,4,5-trisphosphate receptors (IP(3)R) and ryanodine receptors (RyR) mediate the release of endoplasmic and sarcoplasmic reticulum (ER/SR) Ca(2+) stores and regulate Ca(2+) entry through voltage-dependent or ligand-gated channels of the plasma membrane. A prominent property of ER/SR Ca(2+) channels is exquisite sensitivity to sulfhydryl-modifying reagents. A plausible role for sulfhydryl chemistry in physiologic regulation of Ca(2+) release channels and the fidelity of Ca(2+) release from ER/SR is lacking. This study reveals the existence of a transmembrane redox sensor within the RyR1 channel complex that confers tight regulation of channel activity in response to changes in transmembrane redox potential produced by cytoplasmic and luminal glutathione. A transporter selective for glutathione is co-localized with RyR1 within the SR membrane to maintain local redox potential gradients consistent with redox regulation of ER/SR Ca(2+) release. Hyperreactive sulfhydryls previously shown to reside within the RyR1 complex (Liu, G., and Pessah, I. N. (1994) J. Biol. Chem. 269, 33028-33034) are an essential biochemical component of a transmembrane redox sensor. Transmembrane redox sensing may represent a fundamental mechanism by which ER/SR Ca(2+) channels respond to localized changes in transmembrane glutathione redox potential produced by physiologic and pathophysiologic modulators of Ca(2+) release from stores.

Animals↗

PubMed2003

Redox dynamics during recovery of an oil-impacted estuarine wetland.

Redox potentials and sediment porewater parameters were measured around the periphery of a small cove along the San Jacinto River in Texas throughout a crude oil and chemical dispersant remediation study to distinguish normal dynamics from those caused as a response to stress from oil deposition and chemical treatment and subsequent recovery. Before the application of oil and treatments, sediments displayed average redox potentials of 0-350 mV when not submerged. Within 2 days of the applications, redox potentials in these plots decreased and exhibited a range from -200 to 0 mV for a duration of 5 weeks. Applied treatments significantly reduced the sediments of the wetland. Reduced redox potentials were indicative of the corresponding sulfate reduction that was also found to be significant following the oil application. GC/MS and MPN analysis indicates this reduction is due to biological oxidation of the crude oil components by alkane- and PAH-degraders in these surficial sediments and validates the usefulness of the redox measurement as an indicator for carbon oxidation. Increases in aqueous phase total organic and inorganic carbon coincided with a decrease in pH shortly after the applications, suggesting incomplete mineralization and the generation of organic acids. While dissolved ferrous iron and sulfide have been found to be good indicators of reductive processes in petroleum-contaminated aquifer sediments; that was not the case in this wetland study. Despite the disappearance of sulfate following the oil application, dissolved ferrous iron and sulfide concentrations remained at pre-application levels suggesting the formation of mackinawite and/or pyrite. The transient exposure of surface sediments to oxygen complicates the consideration of potential solid phase pathways since aqueous iron may be removed by precipitation when oxidized or reduced, making porewater iron a poor indicator for terminal electron accepting processes in wetland sediments.

Biodegradation, Environmental↗

PubMed1987

Correlations between positive and negative aeroions, tissue redox-state potential and heart frequency in rats.

It was observed in rats that following positive aeroionization the redox-state potential (E'0) in skeletal muscles and liver was decreased, and the heart frequency increased. After negative ionization these interrelationships took place inversely. It was also established that upon adding an oxidant (menadione) i.v., the E'0 was decreased (compensatorily) in the organs mentioned above, parallel with the increment of heart frequency. Following injection of reductants (cysteine, thiamine) a reverse image was observed. Applying simultaneously positive ionization and reducing agents, the E'0 change and the heart frequency alteration failed to appear. The phenomenon was the same after simultaneous application of negative ionization and oxidant (menadione) injection. Because the heart effect of positive and negative ionization could readily be prevented by a respective redox agent, it seemed that actions of aeroions are exerted through shifts in tissue E'0. The most probable site of action of E'0, is the pacemaker mechanism, but an action on serotonin liberation may also be assumed.

Animals↗

PubMed1994

Oxidation-reduction properties of short-chain acyl-CoA dehydrogenase: effects of substrate analogs.

Redox potentials of short-chain acyl-CoA dehydrogenase from the anaerobe, Megasphaera elsdenii, have been determined by means of uv-visible spectroelectrochemistry in the presence of substrate analogs. During redox titrations in the presence of 2-azabutyryl-CoA, up to 85% anionic FAD semiquinone was stabilized with a molar absorbance at 387 nm of 19 mM-1 cm-1. Despite a slow reduction of short-chain acyl-CoA dehydrogenase by 2-azabutyryl-CoA (< 2% reduction/h), a dissociation constant of 0.7 microM was measured and redox potentials, E1(0') and E2(0'), of -0.07 and -0.17 V, respectively, were determined at pH 7.0 for the first and second electrons in reduction of the FAD of short-chain acyl-CoA dehydrogenase. The analog, 2-azoctanoyl-CoA, did not reduce short-chain acyl-CoA dehydrogenase, bound with a dissociation constant of 2 microM, stabilized up to 47% anionic FAD semiquinone, and gave values of -0.08 and -0.11 V for E1(0') and E2(0') at pH 6.9. In contrast to 2-aza-acyl-CoA, the thioethers, butyl-CoA, octyl-CoA, and allyl-CoA, and the thioester, acetyl-CoA, did not bind strongly (Kd > or = 50 microM) and caused no significant change in the redox properties of short-chain acyl-CoA dehydrogenase. The two-electron redox potential, Em, remained at -0.08 V at pH 7.0 and there was no stabilization of FAD semiquinone in the presence of these analogs. These results show that no single feature of substrate structure, the thioester carbonyl, the presence of 2,3-unsaturation, or a fatty alkyl chain of appropriate length, can account for the 0.06-V positive change in redox potential which is observed in the presence of the substrate couple, crotonyl-CoA/butyryl-CoA (M. T. Stankovich and S. Soltysik (1987) Biochemistry 26 2627-2632). As outlined above, 2-azabutyryl-CoA or 2-azaoctanoyl-CoA did cause marked changes in the redox properties of short-chain acyl-CoA dehydrogenase, but the preferential stabilization of FAD semiquinone and negative change in Em distinguish the effects of 2-azaacyl-CoA from those of the substrate couple.

Acyl Coenzyme A↗

PubMed1980

Titrations with ferrocyanide of japanese-lacquer-tree (Rhus vernicifera) laccase and of the type 2 copper-depleted enzyme. Interrelation of the copper sites.

1. Redox titrations are reported of the metal centres in Japanese-lacquer-tree (Rhus vernicifera) laccase with ferrocyanide. 2. The redox potential of Type 1 Cu was found to increase with ferrocyanide concentration up to a limiting value similar to that for the Type 1 Cu in Type 2 Cu-depleted enzyme (which is independent of ferrocyanide concentration). 3. The redox potential of the two-electron acceptor (Type 3 Cu) is also independent of ferrocyanide concentration in Type 2 Cu-depleted enzyme and lower than values reported for the native enzyme. 4. The two-electron acceptor is present in the oxidized state in the Type 2 Cu-depleted enzyme, though the latter lacks the 330 nm absorption band. 5. The redox potential of Type 2 Cu also depends on ferrocyanide concentration, at least in the presence of azide. 6. The redox potentials are affected by freezing the solutions and/or addition of azide, the latter binding to Type 2 Cu with affinity dependent on the redox state of the two-electron acceptor.

Binding Sites↗

PubMed1979

Characterization of two quenchers of chlorophyll fluorescence with different midpoint oxidation-reduction potentials in chloroplasts.

The properties of two redox quenchers of chlorophyll fluorescence in chloroplasts at room temperature have been investigated. (1) Redox titration of the fluorescence yield reveals two n = 1 components with Em7.8 at--45 and --247 mV, accounting for approx. 70 and 30% of the total yield, respectively. (2) Neutral red, a redox mediator often used at redox potentials below --300 mV, preferentially quenches the fluorescence controlled by the --247 mV component. Titrations using neutral red artifactually create an n = 2 quenching component with Em7.8 = --375 mV. (3) Analysis of fluorescence induction curves recorded at different redox potentials indicates that both the --45 and --247 mV components can be photochemically reduced. The reduction of the --247 mV component corresponds to a fast phase of the induction curve whilst the slower reduction of the 45 mV component accounts for the tail phase. (4) The excitation spectra for the fluorescence controlled by the two quenchers show small differences in the ratio of chlorophyll a and b. (5) Whereas the --247 mV component readily shows a 60 mV per pH unit dependency on solution pH, the ability of the --45 mV component to respond to pH change is restricted. (6) Triton Photosystem II particles contain both quenchers but the --247 mV component accounts for approx. 70% of the fluorescence and the high component has an Em7.8 of +48 mV. The relative merits of sequential and parallel models in explaining the presence of the two quenchers are considered.

Chlorophyll↗

PubMed1997

Specific aspects of electron transfer from adrenodoxin to cytochromes p450scc and p45011beta.

An analysis of the electron transfer kinetics from the reduced [2Fe-2S] center of bovine adrenodoxin and its mutants to the natural electron acceptors, cytochromes P450scc and P45011beta, is the primary focus of this paper. A series of mutant proteins with distinctive structural parameters such as redox potential, microenvironment of the iron-sulfur cluster, electrostatic properties, and conformational stability was used to provide more detailed insight into the contribution of the electronic and conformational states of adrenodoxin to the driving forces of the complex formation of reduced adrenodoxin with cytochromes P450scc and P45011beta and electron transfer. The apparent rate constants of P450scc reduction were generally proportional to the adrenodoxin redox potential under conditions in which the protein-protein interactions were not affected. However, the effect of redox potential differences was shown to be masked by structural and electrostatic effects. In contrast, no correlation of the reduction rates of P45011beta with the redox potential of adrenodoxin mutants was found. Compared with the interaction with P450scc, however, the hydrophobic protein region between the iron-sulfur cluster and the acidic site on the surface of adrenodoxin seems to play an important role for precise complementarity in the tightly associated complex with P45011beta.

Adrenodoxin↗

PubMedDate not supplied

[The redox status of the blood plasma in cattle from ecological farming--1. Influence of genotype and age on the antioxidant defence capacity in the blood plasma].

The present study examined the effects of race and age on the redox potential behavior of blood plasma samples. The oxidative stability was studied in the reaction with p-benzoquinone. The investigated animals represented three different cattle races (Limousin, Angus and Hereford), grazed on pasture. The blood samples from clinical healthy heifers (44) and calves (45) were investigated. The following parameters were determined: the start level of redox potential and the level after adding 10, 20, and 30 mg p-benzoquinone to the samples. The analyses of the redox potentials showed the advantage of oxidative stability of heifers compared with calves. The results showed a significant effect of race on the redox potential behavior of blood plasma.

Age Factors↗

PubMed2004

Studies on hydrogenase activity and chlorobenzene respiration in Dehalococcoides sp. strain CBDB1.

Hydrogen oxidation and electron transport were studied in the chlorobenzene-utilizing anaerobe Dehalococcoides sp. strain CBDB1. While Cu(2+) and Hg(2+) ions irreversibly inhibited hydrogenase activity in intact cells, Ni(2+) ions inhibited reversibly. About 80% of the initial hydrogenase activity was inactivated within 30 s when the cells were exposed to air. In contrast, hydrogenase was active at a redox potential of +10 mV when this redox potential was established anoxically with a redox indicator. Viologen dyes served both as electron acceptor for hydrogenase and electron donor for the dehalogenase. A menaquinone analogue, 2,3-dimethyl 1,4-naphthoquinone, served neither as electron acceptor for the hydrogenase nor as electron donor for the dehalogenase. In addition, the menaquinone antagonist 2-n-heptyl-4-hydroxyquinoline-N-oxide had no effect on dechlorination catalyzed by cell suspensions or isolated membranes with hydrogen as electron donor, lending further support to the notion that menaquinone is not involved in electron transport. The ionophores tetrachlorosalicylanilide and carbonylcyanide m-chlorophenylhydrazone did not inhibit dechlorination by cell suspensions, indicating that strain CBDB1 does not require reverse electron transport. The ATP-synthase inhibitor N,N'-dicyclohexylcarbodiimide inhibited the dechlorination reaction with cell suspensions; however, the latter effect was partially relieved by the addition of tetrachlorosalicylanilide. 1,2,3,4-tetrachlorobenzene strongly inhibited dechlorination of other chlorobenzenes by cell suspensions with hydrogen as electron donor, but it did not interfere with either hydrogenase or dehalogenase activity.

Chlorobenzenes↗