Search PubMed⌕ Search

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.

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

At least 55 records · Page 3Linked to original sources
PubMed1996

Elucidating the mechanism of nucleotide-dependent changes in the redox potential of the [4Fe-4S] cluster in nitrogenase iron protein: the role of phenylalanine 135.

Nucleotide binding to the nitrogenase iron (Fe) protein results in a lowering of the redox potential of its [4Fe-4S] cluster by over 100 mV, and this is thought to be essential for electron transfer to the molybdenum-iron (MoFe) protein for substrate reduction. This work presents evidence for an important role of the strictly conserved phenylalanine at position 135, located near the [4Fe-4S] cluster of nitrogenase Fe protein, in defining both the redox potential and the nucleotide-induced changes in the redox potential of the [4Fe-4S] cluster. Phe 135 was changed by means of site-directed mutagenesis to the amino acids Tyr (F135Y), Ile (F135I), Trp (F135W), and His (F135H), and the altered proteins were purified to homogeneity. Minor changes in the UV/visible and EPR spectra arising from the [4Fe-4S] cluster were detected in the altered proteins, while dramatic changes were observed in the visible region circular dichroism (CD) spectrum, suggesting that Phe 135 contributes significantly to the chiroptical properties of the [4Fe-4S] cluster. Likewise, significant changes in the redox potentials of the Phe altered Fe proteins were observed, with shifts of +50 to +120 mV compared to the redox potential of the wild-type Fe protein (-300 mV). The shifts in redox potential for the altered Fe proteins appeared to correlate with changes in isotropically shifted proton NMR resonances assigned to cluster ligands. All of the Phe 135 altered Fe proteins were found to bind either MgADP or MgATP, while the reduced and oxidized states of the F135W and F135H altered Fe proteins had significantly higher affinities for binding MgATP when compared to the wild-type Fe protein. While MgATP binding to the wild-type and Phe 135 altered Fe proteins resulted in approximately -100 mV shifts in the redox potentials for all proteins, MgADP binding resulted in only -30 to -50 mV shifts for the altered proteins compared to a -160 mV shift for the wild-type Fe protein. The current results suggest that Phe 135 is important in defining the redox potential of the [4Fe-4S] cluster in the Fe protein and influences the MgADP (but not MgATP) induced modulation of the redox potential.

Adenosine Diphosphate↗
PubMed2000

The effect of mutation at valine-45 on the stability and redox potentials of trypsin-cleaved cytochrome b5.

In an attempt to elucidate the determinants of redox potential and protein stability in cytochrome b5, three mutants at a highly conserved residue Val45, which is a member of heme hydrophobic pocket residues have been characterized. The V45Y mutant was designed to introduce a bulkier residue and a hydroxyl group to the heme pocket. The mutants V45H and V45E were constructed to test the effect of positive and negative charge on the stability and redox potential of proteins. The influence of these mutants on the protein stability towards thermal, urea, acid, ethanol and on the redox potential were studied. It is concluded that the decrease of hydrophobic free energy and the larger volume of the tyrosine make the phenylhydroxyl group of tyrosine still sitting inside the hydrophobic pocket, while the side chain of the mutant V45E and V45H shift away from the heme pocket. The redox potentials of mutants V45Y, V45H, V45E and wild-type of cytochrome b5 are -35 mV, 8 mV, -26 mV and -3 mV, respectively. The bigger change of the V45Y on redox potential is due to the close contact between the hydroxyl group and the heme, while the changes of the V45E and V45H result from the alteration of charge density and distribution around the heme. Different relative stability of these mutants towards heat have been observed with the order: WT > V45Y-V45H > V45E being both in the oxidized and reduced state. The relative stability induced by addition of urea decreases in the order: WT > V45Y > V45H > V45E. These results suggest that the difference in the hydrophobic free energy is a major factor contributing to the stability of the Val45 mutants. Also the loose of the helix III in the mutant V45E makes it more unstable. These results indicate that residue Val45 plays an important role in the stability and redox potential of the protein.

Acids↗
PubMed2003

Tuning heme redox potentials in the cytochrome C subunit of photosynthetic reaction centers.

The photosynthetic reaction center (RC) from Rhodopseudomonas viridis contains four cytochrome c hemes. They establish the initial part of the electron transfer (ET) chain through the RC. Despite their chemical identity, their midpoint potentials cover an interval of 440 mV. The individual heme midpoint potentials determine the ET kinetics and are therefore tuned by specific interactions with the protein environment. Here, we use an electrostatic approach based on the solution of the linearized Poisson-Boltzmann equation to evaluate the determinants of individual heme redox potentials. Our calculated redox potentials agree within 25 meV with the experimentally measured values. The heme redox potentials are mainly governed by solvent accessibility of the hemes and propionic acids, by neutralization of the negative charges at the propionates through either protonation or formation of salt bridges, by interactions with other hemes, and to a lesser extent, with other titratable protein side chains. In contrast to earlier computations on this system, we used quantum chemically derived atomic charges, considered an equilibrium-distributed protonation pattern, and accounted for interdependencies of site-site interactions. We provide values for the working potentials of all hemes as a function of the solution redox potential, which are crucial for calculations of ET rates. We identify residues whose site-directed mutation might significantly influence ET processes in the cytochrome c part of the RC. Redox potentials measured on a previously generated mutant could be reproduced by calculations based on a model structure of the mutant generated from the wild type RC.

Binding Sites↗
PubMed2003

Cytochrome c, glutathione, and the possible role of redox potentials in apoptosis.

The redox environment of the cell is now thought to be extremely important to control the activity of many proteins. During apoptosis, the intracellular redox potential (E(h)) becomes more positive, with possible consequences for the mechanisms of apoptosis. Glutathione and cytochrome c might both influence and be influenced by the cellular redox environment and therefore be important in the progression of apoptosis.

Animals↗
PubMed2003

Effect of redox potential on stationary-phase xylitol fermentations using Candida tropicalis.

Redox potential was used to develop a stationary-phase fermentation of Candida tropicalis that resulted in non-growth conditions with a limited decline in cell viability, a xylitol yield of 0.87 g g(-1) (95% of the theoretical value), and a high maximum specific production rate (0.67 g g(-1) h(-1)). A redox potential of -100 mV was found to be optimum for xylitol production over the range 0-150 mV [correction]. A shift from ethanol to xylitol production occurred when the redox potential was reduced from 50 mV to 100 mV as cumulative ethanol (Y(ethanol)) decreased from 0.34 g g(-1) to 0.025 g g(-1) and Y(xylitol) increased from 0.15 g g(-1) to 0.87 g g(-1) (alpha=0.05). Reducing the redox potential to 150 mV did not improve the fermentation. Instead, the xylitol yield and productivity decreased to 0.63 g g(-1) and 0.58 g g(-1) h(-1) respectively and cell viability declined. The viable, stationary-phase fermentation could be used to develop a continuous fermentation process, significantly increasing volumetric productivity and reducing downstream separation costs, potentially by the use of a membrane cell-recycle reactor.

Bioreactors↗
PubMed2003

Redox potentials of the oriented film of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins.

The redox potentials of the oriented films of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins (bR), prepared by adsorbing purple membrane (PM) sheets or its mutant on a Pt electrode, have been examined. The redox potentials (V) of the wild-type bR were -470 mV for the 13-cis configuration of the retinal Shiff base in bR and -757 mV for the all-trans configuration in H(2)O, and -433 mV for the 13-cis configuration and -742 mV for the all-trans configuration in D(2)O. The solvent isotope effect (DeltaV=V(D(2)O)-V(H(2)O)), which shifts the redox potential to a higher value, originates from the cooperative rearrangements of the extensively hydrogen-bonded water molecules around the protonated C=N part in the retinal Schiff base. The redox potential of bR was much higher for the 13-cis configuration than that for the all-trans configuration. The redox potentials for the E194Q mutant in the extracellular region were -507 mV for the 13-cis configuration and -788 mV for the all-trans configuration; and for the E204Q mutant they were -491 mV for the 13-cis configuration and -769 mV for the all-trans configuration. Replacement of the Glu(194) or Glu(204) residues by Gln weakened the electron withdrawing interaction to the protonated C=N bond in the retinal Schiff base. The E204 residue is less linked with the hydrogen-bonded network of the proton release pathway compared with E194. The redox potentials of the D96N mutant in the cytoplasmic region were -471 mV for the 13-cis configuration and -760 mV for the all-trans configuration which were virtually the same as those of the wild-type bR, indicating that the D to N point mutation of the 96 residue had no influence on the interaction between the D96 residue and the C=N part in the Schiff base under the light-adapted condition. The results suggest that the redox potential of bR is closely correlated to the hydrogen-bonded network spanning from the retinal Schiff base to the extracellular surface of bR in the proton transfer pathway.

Bacteriorhodopsins↗
PubMed2004

Premature Salmonella Typhimurium growth inhibition in competition with other Gram-negative organisms is redox potential regulated via RpoS induction.

AIMS: To identify the role of oxidation-reduction (redox) potential in the premature growth inhibition and RpoS induction in Salmonella serotype Typhimurium in competitive growth experiments. METHODS AND RESULTS: Oxidation-reduction potential was measured throughout the growth of a minority population of Salm. Typhimurium in mixed cultures with other Gram-negative and Gram-positive organisms. A lux-based reporter was also used to evaluate RpoS activity in Salm. Typhimurium in competitor studies. In a mixed culture, the multiplication of a minority population of Salm. Typhimurium was inhibited when competing Gram-negative organisms entered the stationary phase. This was not seen when the competing flora was Gram-positive. The change in redox potential during growth in mixed cultures was closely linked to the inhibition of Salm. Typhimurium growth by Gram-negative competitors. An artificially induced drop in redox potential earlier during growth in mixed cultures with Gram-negative organisms reduced the time to RpoS induction in Salm. Typhimurium and thus inhibited its multiplication prematurely. In contrast, RpoS induction and growth inhibition were prevented under high redox potential conditions. CONCLUSIONS: This work shows that the inhibitory activity of competitive organisms can be mediated through their effect on redox potential-regulated RpoS induction. SIGNIFICANCE AND IMPACT OF THE STUDY: Redox potential is shown to be an important determinant of Salm. Typhimurium growth, an observation with practical implications both for its control and detection.

Antibiosis↗
PubMed1981

The effects of pH and redox potential on the hydrogen production activity of the hydrogenase from Megasphaera elsdenii.

The effects of temperature on the ionization constant (pK') and apparent midpoint potential (EB) of the unprotonated species of Megasphaera elsdenii flavodoxin hydroquinone shows that, above 15 degrees C, delta pK' . K-1 = -9.7 X 10(-3) and delta EB . K-1 = -0.6 mV. The effects of pH and redox potential on the hydrogen production activity with fixed concentrations of methyl viologen semiquinone (0.3 mM; artificial donor) and M. elsdenii flavodoxin hydroquinone (50 microM; natural donor) show that with decreasing pH the activity increases. Irrespective of the pH and electron donor, at increasing redox potential, a redox-potential-independent production activity is followed by a redox-potential-dependent production activity. This redox-potential-dependent behaviour of the hydrogen production activity represents an n = 2-type of redox titration curve with an 'apparent midpoint potential' which corresponds with the potential of the hydrogen electrode at that pH. The effect of pH on the manometrically determined hydrogen production activity (direct) is in good agreement with that determined spectrophotometrically (indirect; see preceding paper), with both electron donors tested. In contrast to predictions from the models for hydrogenase activity [van Dijk et al. (1980) Eur. J. Biochem.102, 317--330], a double-reciprocal plot of the kinetic data for M. elsdenii flavodoxin hydroquinone at pH 5.5 is non-linear. A slightly adapted kinetic model based on a similar mathematical formulation of its rate equation, to explain the effects of redox potential, proton and electron (donor) concentration on the hydrogenase activity is proposed. This model also explains, on a theoretical basis, the effects of pH and redox potential on the hydrogen production activity. The effect of pH on the hydrogen oxidation activity with methyl viologen and benzyl viologen as electron acceptors shows for both dyes an optimum at pH 9.7. The ratio of the activities with both viologens is constant over the ph range tested.

Hydrogen-Ion Concentration↗
PubMed1978

[Redox potentials of some metalloproteins].

The standard redox potentials of soluble cytochromes c isolated from the green alga Chlorella and the blue-green algae Spirulina and Aphanezomenon were determined by potentiometric titration and found to be equal to +380 mB, +330 mB and +357 AB, respectively. The standard redox potentials of plastocyanin preparations from Pisum sativum and Atriplex leaves were also determined and found close to those of soluble cytochromes c, i. e. +395 mB and +375 mB, respectively. The metalloproteins studied were shown to belong to monoelectron carriers operating at the donor sites of photosystem I.

Chlorella↗
PubMed1998

Redox potential affects the measured heat resistance of Escherichia coli O157:H7 independently of oxygen concentration.

Cells of Escherichia coli O157:H7 were heat-treated at 59 degrees C and enumerated in (i) anaerobic medium with a low redox potential, (ii) anaerobic media with the oxidizing agents potassium ferricyanide or 2,6-dichloroindophenol (DPIP) added to raise the redox potential, (iii) aerobic medium with a high redox potential and (iv) aerobic medium with the reducing agent dithiothreitol added to lower the redox potential. The measured heat-resistance was greatest when the enumeration medium was highly anaerobic due to the absence of oxygen and the presence of hydrogen and cysteine HCl. Measured heat resistance was influenced by the redox potential of the enumeration medium independently of the chemical used to adjust it and therefore, independently of the presence of oxygen. Sub-lethally heat-damaged cells regained their ability to grow in media of high redox potential at a similar rate whether the redox potential was increased by the addition of potassium ferricyanide, DPIP or oxygen.

Escherichia coli↗
PubMed2007

Redox potential measurement as a rapid method for microbiological testing and its validation for coliform determination.

The redox potential is one of the most complex indicators of the physiological state of microbial cultures and its measurement could be a useful tool for the qualitative and quantitative determination of the microbial contamination. During the bacterial growth, the redox potential of the medium decreases. The shape of the redox potential curve is characteristic on the type of microorganism, and the rate of the change (dE/dt) is proportional to the living cell concentration. Defining the time required to reach a significant change in redox potential as Time to Detection (TTD), similarly to the impedimetric measurements, a strict linear correlation could be established between the TTD and the logarithm of the initial concentration of microorganisms. On the base of this calibration curve, the determination of living cell concentration could be simplified. For the experiments, a computer-controlled multi-channel measuring system and software was developed by the authors. The redox potential measurement method was tested and validated for the determination of coliform bacteria. The results have proved the high efficiency and reliability of the new method.

Area Under Curve↗
PubMed2001

Effects of redox potential and pH value on the release of rare earth elements from soil.

Equilibrium release experiments were conducted under three different pH values of 3.5, 5.5 and 7.5 as well as three redox potentials of 400, 0 and -100 Mv to investigate the influence of redox potential and pH value on the La, Ce, Gd and Y release of from the simulated-REEs-accumulation (SRA) soil. Oxygen and nitrogen were allowed to flow into soil suspension to adjust redox potential to a preset value, and 1 mol/l HCl or 1 mol/l NaOH solutions were added into the soil suspension to keep pH at a preset value. Results indicated that La, Ce, Gd and Y release increased gradually with the decrease of pH value or Eh, and the influence of redox potential on Ce was more remarkable than on La, Gd and Y. At the same time. It was observed that La, Ce, Gd and Y releases were positively correlated with the release of Fe and Mn, indicating that La, Ce, Gd and Y releases might originate from dissolution of Fe-Mn oxyhydroxides under reduction and low pH conditions. Moreover, it was found that alteration of pH value and redox potential might affect the change of La, Ce, Gd and Y species in the soil. The contents of La, Ce, Gd and Y in exchangeable fraction and Fe-Mn oxide fraction in the solid phase from soil suspension separation decreased with the decline of pH value and redox potential. Multiple stepwise regression analysis showed that exchangeable fraction and Fe-Mn oxide fraction predominately contributed to the La, Ce, Gd and Y release. Low pH value and redox potential were more favorable to La, Ce, Gd and Y releases following the change of their species. The La, Ce, Gd and Y contents in exchangeable fraction and Fe-Mn oxide fraction are the main contributors to their release.

Biological Availability↗
PubMed2005

Significant species-dependence of P700 redox potential as verified by spectroelectrochemistry: comparison of spinach and Theromosynechococcus elongatus.

The redox potentials of P700, the primary electron donor of photosystem (PS) I, of spinach and Thermosynechococcus elongatus were determined by means of spectroelectrochemistry with an error range of +/-2-3 mV, to find that the redox potential of P700 in T. elongatus is lower by ca. 50 mV as compared with spinach. The shift in the P700 redox potential of PS I core particles prepared by harsh detergent treatments remained to within 10 mV for both organisms. These results show that the 50 mV difference in the P700 redox potential between the two organisms is not a detergent-induced artifact but reflects an intrinsic property of each PS I.

Cyanobacteria↗
PubMed1999

Importance of redox potential for the in vivo function of the cytoplasmic disulfide reductant thioredoxin from Escherichia coli.

The thioredoxin superfamily consists of enzymes that catalyze the reduction, formation, and isomerization of disulfide bonds and exert their activity through a redox active disulfide in a Cys-Xaa(1)-Xaa(2)-Cys motif. The individual members of the family differ strongly in their intrinsic redox potentials. However, the role of the different redox potentials for the in vivo function of these enzymes is essentially unknown. To address the question of in vivo importance of redox potential for the most reducing member of the enzyme family, thioredoxin, we have employed a set of active site variants of thioredoxin with increased redox potentials (-270 to -195 mV) for functional studies in the cytoplasm of Escherichia coli. The variants proved to be efficient substrates of thioredoxin reductase, providing a basis for an in vivo characterization of NADPH-dependent reductive processes catalyzed by the thioredoxin variants. The reduction of sulfate and methionine sulfoxide, as well as the isomerization of periplasmic disulfide bonds by DsbC, which all depend on thioredoxin as catalyst in the E. coli cytoplasm, proved to correlate well with the intrinsic redox potentials of the variants in complementation assays. The same correlation could be established in vitro by using the thioredoxin-catalyzed reduction of lipoic acid by NADPH as a model reaction. We propose that the rate of direct reduction of substrates by thioredoxin, which largely depends on the redox potential of thioredoxin, is the most important parameter for the in vivo function of thioredoxin, as recycling of reduced thioredoxin through NADPH and thioredoxin reductase is not rate-limiting for its catalytic cycle.

Cytoplasm↗
PubMed1976

The one-electron transfer redox potentials of free radicals. I. The oxygen/superoxide system.

The method of determination of Redox potentials of radicals, using the pulse radiolysis technique, is outlined. The method is based on the determination of equilibrium constants of electron transfer reactions between the radicals and appropriate acceptors. The limitations of this technique are discussed. The redox potentials of several quinones-semiquinones are calculated, as well as the standard redox potential of the peroxy radical. EO2/O2=-0.33 V and the redox oxidation properties of the peroxy radical in various systems and pH are discussed. The value determined for the redox potentials of O2/O2 is higher by more than 0.2 V than earlier estimates, which has important implications on the possible role of O2 in biological processes of O2 fixation.

Electron Transport↗
PubMed1993

Control of gene expression by redox potential and the requirement for chloroplast and mitochondrial genomes.

Recent experiments with bacteria have shown that light and oxygen can control gene expression through effects on oxidation-reduction potential. The term "redox sensor" is proposed as a general term for electron carriers that initiate control of gene expression upon oxidation or reduction. The term "redox response regulator" is proposed for DNA-binding proteins that modify gene expression as a result of the action of redox sensors. Redox sensors and redox response regulators may function together in feedback control of redox potential in photosynthesis and respiration, protecting the cell from damage caused by electrochemistry operating on inappropriate electron donors and acceptors. Chloroplast and mitochondrial redox sensors and redox response regulators, themselves encoded in the nucleus, may place expression of chloroplast and mitochondrial genes under redox regulatory control. This hypothesis offers an explanation for the persistence, in evolution, of chloroplast and mitochondrial genomes, and for the constancy of the subset of chloroplast and mitochondrial proteins encoded and synthesized within the organelle.

Animals↗
PubMed1989

Significance of hepatic mitochondrial redox potential on the concentrations of plasma amino acids following hemorrhagic shock in rats.

The changes in hepatic energy charge, hepatic mitochondrial redox potential, and plasma amino acid concentrations were examined in rats following the induction of hemorrhagic shock with mean arterial blood pressure at 50 mmHg. Hepatic energy charge and mitochondrial redox potential decreased significantly (P less than 0.001), from 0.86 +/- 0.01 to 0.49 +/- 0.05 and from 14.4 +/- 0.8 to 2.9 +/- 0.6, respectively, at 2 hours after the induction of hemorrhagic shock. Concentrations of total amino acids, alanine, proline, tyrosine, and phenylalanine in plasma increased, and molar ratio [( valine + leucine + isoleucine]/[tyrosine + phenylalanine]) in plasma decreased significantly (P less than 0.001). Hepatic mitochondrial redox potential was correlated negatively with total amino acids (r = -0.90, P less than 0.001) and positively with molar ratio (r = 0.85, P less than 0.001) during hemorrhagic shock. By reinfusion of shed blood at 2 hours after hemorrhagic shock, hepatic energy charge and mitochondrial redox potential immediately recovered to the pretreatment level. However, total amino acids, proline, tyrosine, and phenylalanine increased transiently and thereafter decreased to the pretreatment level. Molar ratio did not recover even at 60 minutes after reinfusion. These results suggest that, in hemorrhagic shock, reduced hepatic mitochondrial redox potential causes inhibition of the citric acid cycle metabolizing the amino acids in the liver and an increase of plasma amino acids; these results suggest also that, in the recovery phase from shock, the restoration of hepatic mitochondrial redox potential is a prerequisite for normalization of the accumulated plasma amino acids.

Adenine Nucleotides↗
PubMed2006

Influence of electron donor, oxygen, and redox potential on bacterial perchlorate degradation.

Experiments were conducted to assess the influence of electron donor, redox potential, and dissolved oxygen on bacterial perchlorate degradation. Microcosms containing a diverse, perchlorate-acclimated, bacterial culture fed lactate at a 1:1 electron donor-to-perchlorate ratio (electron-equivalent basis) degraded perchlorate more slowly (k = 0.038 mg ClO4-/mg VSS h) and to a lesser extent than microcosms fed lactate at 2:1 and 4:1 ratios (k = 0.045 mg ClO4-/mg VSS h). The optimal COD/ClO4- ratio to consume all perchlorate and all electron donor was approximately 1.2 mg COD/mg ClO4-. In experiments where the redox potential was held constant, the extent of perchlorate degradation increased with decreasing redox potential, and 100% removal was only achieved at the lowest redox potential examined (-220 mV); however, perchlorate degradation (32% of added perchlorate) was observed as high as +180 mV. Additions of oxygen to actively degrading treatments did not adversely effect perchlorate degradation. It appears, therefore, that addition of excess electron donor is sufficient to negate potential inhibitory effects of molecular oxygen. If the redox conditions are more oxidized, however, the rate and extent of perchlorate degradation will be significantly decreased. This is the first report of perchlorate degradation under oxidized conditions using an environmentally relevant, diverse, bacterial enrichment culture, and this is also the first report of perchlorate reduction occurring at appreciable dissolved oxygen concentrations in a batch system.

Bacteria↗