Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “OXIDATION REDUCTION”

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 73 records · Page 4Linked to original sources
PubMed1994

The voltage sensor of the mitochondrial permeability transition pore is tuned by the oxidation-reduction state of vicinal thiols. Increase of the gating potential by oxidants and its reversal by reducing agents.

Reaction of isolated mitochondria with a variety of agents that lead to oxidation or cross-linking of sulfhydryl groups leads to an increased "open" probability of the permeability transition pore, a cyclosporin A-sensitive channel. We have investigated the mechanism by which the pore is induced by menadione, diamide, arsenite, and tert-butylhydroperoxide. We find that these inducers increase the probability of pore opening by shifting its gating potential to higher values. Furthermore, the induced shift was prevented by treatment with N-ethylmaleimide or dithiothreitol. At moderate levels of depolarization an apparent I50 for N-ethylmaleimide of bout 5 microM can be defined, while the N-ethylmaleimide or dithiothreitol effects are overcome by maximal depolarization. We conclude that the oxidation-reduction state of vicinal thiols in cysteinyl residues plays a critical role in tuning the voltage sensor of the transition pore, with an increase of gating potential (i.e. an increase in the probability of pore opening despite a high transmembrane potential difference) as the couple is poised to a more oxidized state. These findings may have implications for the mechanism of cell damage under oxidative stress.

Animals↗
PubMed1975

Oxidation-reduction potentials of human fetal hemoglobin and gamma chains. Effects of blocking sulfhydryl groups.

The oxidation-reduction equilibrium of the gamma chains of human fetal hemoglobin (Hb F) has been studied and compared with that of the alpha and beta chains of human adult hemoglobin (Hb A). The effects of the sulfhydryl (--SH) reagents, iodoacetate, iodoacetamide, and p-mercuribenzoate (PMB), on the three kinds of chains and on Hb F have been compared. The midpoint potentials (E-m) of all three sorts of chains are lower than those of tetrameric hemoglobin A or F. The E-m values of alpha chains are the lowest, E-m = 0.049 volt at 6 degrees, and are unaffected by pH change or by PMB treatment, at least from pH 6 to 8. The E-m values of beta-SH chains are higher; E-m = 0.102 volt at pH 7, decreasing to 0.050 volt at pH 8, both at 6 degrees. These results agree with those of Banerjee and Cassoly ((1969) J. Mol. Biol. 42, 337-349). They reported no effect of PMB on beta chains, but we find that 2 eq of PMB/chain raise E--M to 0.139 volt at pH 7 at 6 degrees, chiefly as the result of reaction at beta-93, not at beta-112. Carboxymethylation at beta-93 has an insignificant effect compared with that of PMB. The oxidation-reduction potential of gamma chains is similar to that of beta chains. E-m = 0.098 volt at pH 7 at 6 degrees, decreasing to 0.064 at pH 8 and 0.010 at pH 9. The effects of --SH reagents, reacting at position gamma-93 (the only --SH group present in gamma chains), are essentially the same as those seen with beta chains. The oxidation-reduction potential of Hb F is almost identical with that of Hb A, except for being 0.008 volt lower at pH 6 at 6 degrees. This agrees with the results reported by Flohe and Uehleke ((1966) Life Sci. 5, 1041-1045). PMB or iodoacetamide treatment lowers E-m by 0.02 to 0.03 volt, depending on the pH, from 6 to 9, in much the same way as previously reported for Hb A(Brunori, M., Taylor, J.F., Antonini, E., Wyman, J., and Rossi-Fanelli, A. (1967) J. Biol. Chem. 242, 2295-2300). The "residual oxidation Bohr effect" noted in Hb F can be attributed to the oxidation Bohr effect of the gamma chains. The apparent pK of the heme-linked water molecule was found at 25 degrees to be, for Hb F, 8.1; for gamma-SH chains, 7.85; for gamma-PMB chains, 8.35; and for gamma chains treated with iodoacetate, 7.80. Sedimentation coefficients, s-20, w, at a protein concentration of 5 mg/ml, were found to be, for fetal hemoglobin 4.09, for iodoacetamide-treated fetal hemoglobin 4.04, for PMB-treated fetal hemoglobin 3.41, for fetal gamma-SH chains 4.25, and for fetal gamma-PMB chains 3.08.

Adult↗
PubMed1975

Differential effects of oxygen and oxidation-reduction potential on the multiplication of three species of anaerobic intestinal bacteria.

The sensitivity of three strains of anaerobic intestinal bacteria, Clostridium perfringens, Bacteroides fragilis, and Peptococcus magnus, to the differential effects of oxygen and adverse oxidation-reduction potential was measured. The multiplication of the three organisms was inhibited in the presence of oxygen whether the medium was at a negative oxidation-reduction potential (Eh of -50 mV), poised by the intermittent addition of dithiothreitol, or at a positive oxidation-reduction potential (Eh of near +500 mV). However, when these organisms were cultured in the presence of oxygen, no inhibition was observed, even when the oxidation-reduction potential was maintained at an average Eh of +325 mV by the addition of potassium ferricyanide. When the cultures were aerated, the growth patterns of the three organisms demonstrated different sensitivities to oxygen. P. magnus was found to be the most sensitive. After 2 h of aerobic incubation, no viable organisms could be detected. B. fragilis was intermediately sensitive to oxygen with no viable organisms detected after 5 h of aerobic incubation. C. perfringens was the least sensitive. Under conditions of aerobic incubation, viable organisms survived for 10 h. During the experiments with Clostridium, no spores were observed by spore staining.

Anaerobiosis↗
PubMedDate not supplied

[Effects of the thiol reagent dithiothreitol on the oxidation-reduction potential and the growth of Escherichia coli in anaerobic conditions at different pH].

Changes in the oxidation-reduction potential of medium during the growth of Escherichia coli bacteria under anaerobic conditions in the pH range 5.5-7.5 were studied. It was shown that dithiothreitol, a reducer of thiol groups, at a concentration of 3 mM decreased the initial value of oxidation-reduction potential to negative values of -60 to -220 mV, increased the duration of the lag growth phase, decreased the growth rate, and lowered the acidification of the medium and accumulation of potassium ions independently of pH. The value of the potential in the presence of 3 mM dithiothreitol decreased by 15-20 mV both at alkaline and acidic pH. Dithiothreitol at a concentration of 10 mM stopped molecular hydrogen production at pH 5.5 only. The effects of dithiothreitol on the oxidation-reduction potential and bacterial growth were probably associated with changes in the state of thiol groups in membrane proteins, which affects the generation of membrane potential, proton secretion from cells, K+ accumulation in bacteria, and the activity of membrane-associated enzymes.

Anaerobiosis↗
PubMed1988

Oxidation-reduction potential studies on p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens.

The oxidation-reduction potential of p-hydroxybenzoate hydroxylase (4-hydroxybenzoate, NADPH: oxygen oxidoreductase (3-hydroxylating), EC 1.14.13.2) from Pseudomonas fluorescens has been measured in the presence and absence of p-hydroxybenzoate using spectrocoulometry. The native enzyme demonstrated a two-electron midpoint potential of -129 mV during the initial reductive titration. The midpoint potential observed during subsequent oxidative and reductive titrations was -152 mV. This marked hysteresis is proposed to arise from the oxidation and reduction of the known air-sensitive thiol group on the enzyme (Van Berkel, W.J.H. and Müller, F. (1987) Eur. J. Biochem. 167, 35-46). Redox titrations of the enzyme in the presence of substrate showed a two-electron midpoint potential of -177 mV. No spectral or electrochemical evidence for the thermodynamic stabilization of any flavin semiquinone was observed in the titrations performed. These data show that the affinity of the apoenzyme for the hydroquinone form of FAD is 150-fold greater than for the oxidized flavin and that the substrate is bound to the reduced enzyme with a 3-fold lower affinity than to the oxidized enzyme. These data are consistent with the view that the stimulatory effect of substrate binding on the rate of enzyme reduction by NADPH is due to the respective geometries of the bound FAD and NADPH rather than to a large perturbation of the oxidation-reduction potential of the bound flavin coenzyme.

4-Hydroxybenzoate-3-Monooxygenase↗
PubMed1998

Oxidation-reduction properties of the regulatory site of spinach phosphoribulokinase.

The oxidation-reduction midpoint potential (Em) of the regulatory disulfide, formed between Cys16 and Cys55, of spinach chloroplast phosphoribulokinase has been determined both for the wild-type enzyme and for a C244S-C250S double mutant, using enzymatic activity to monitor the oxidation-reduction state of the regulatory disulfide. At pH 7.0, Em values for the two-electron reduction of the regulatory disulfide of -295 +/- 10 and -290 +/- 10 mV were measured for the wild-type and mutant, respectively. In contrast to the dependence of activity on ambient potential (Eh) observed for the wild-type enzyme and the double mutant, which both followed the Nernst equation for a two-electron process, high and constant activity was exhibited by a C16S-C244S-C250 triple mutant of the enzyme at all Eh values tested. Em values for the wild-type enzyme were also measured at pH values of 6.7, 7.5, 7.7, and 8.2 and the Em vs pH data in this region give a good fit to a straight line with a slope of -60 mV/pH unit.

Chloroplasts↗
PubMed2006

Phosphopeptide modification and enrichment by oxidation-reduction condensation.

Many cellular processes are regulated by the reversible phosphorylation of proteins. Despite the importance of monitoring protein phosphorylation, available methods to modify and enrich phosphopeptides from complex mixtures for subsequent mass spectrometric analysis are challenging. Here the oxidation-reduction condensation was shown for the first time to directly modify the phosphate of phosphopeptides and phosphoproteins. By coupling with a solid-phase resin, the oxidation-reduction condensation was validated for capture and recovery of phosphoserine-, phosphothreonine-, and phosphotyrosine-containing peptides from a peptide mixture. In addition, full-length phosphoproteins or phosphopeptides from a protein digestion were captured and recovered using the oxidation-reduction condensation, demonstrating its compatibility with protein mixtures. The strategy modifies all phosphopeptides, maintains high chemical selectivity, requires only two steps, and relies on commercially available reagents, suggesting that the oxidation-reduction condensation has the potential to enhance phosphopeptide enrichment methods and encourage development of efficient biochemical and proteomics tools targeting phosphorylation.

Amino Acid Sequence↗
PubMed1999

In vivo oxidation-reduction kinetics of OxyR, the transcriptional activator for an oxidative stress-inducible regulon in Escherichia coli.

The OxyR protein is a transcriptional activator for a subset of peroxide stress-inducible genes, most of which are involved in defense systems against oxidative stress. Recently, it was demonstrated that purified OxyR has one intramolecular disulfide bond, which led to the proposal that the reversible disulfide bond formation regulates the activity of OxyR as a transcription factor in response to peroxide stress. In this study, I demonstrated by SDS-PAGE under non-reducing conditions that an intramolecular disulfide bond is formed in OxyR upon exposure of the cells to hydrogen peroxide in vivo. Experiments using strains expressing mutant OxyR proteins with Cys to Ser single amino acids substitutions confirmed that the disulfide bond is formed between the Cys-199 and -208. Kinetic analyses indicated that the formation of the disulfide bond is rapid and transient, oxidized within 30 s and re-reduced within 5 min after the addition of hydrogen peroxide in the wild-type strain. These results provide evidence for the regulatory role of the reversible oxidation of dithiol to disulfide in sensing peroxide stress in vivo and signal transduction to the transcription apparatus by OxyR.

Cysteine↗
PubMed1976

Non-equivalence of human hemoglobin chains in the oxidation-reduction and heme-transfer reactions. A 13C nuclear-Magnetic-resonance study.

12C nuclear magnetic resonance (NMR) spectroscopy has been applied to the investigation of chain non-equivalence for two reactions of human hemoglobin: oxidation-reduction and hemetransfer. The method is based on previous observations that in the carbonyl region, Hb13CO gives two well-resolved resonances which arise from 13C of carbonyls bound respectively to the alpha and beta chains; moreover, integration of spectra allows on e to estimate their relative abundance. A mixture of ferrous and ferric hemoglobins in dye-mediated oxidation-reduction equilibrium can be formally considered to be equivalent to two redox couples in equilibrium, namely alphaIII/alphaII and betaIII/betaII; from a knowledge of these ratios, one can conclude whether the chains are equivalent or not in their oxidation-reduction properties. In this work, these ratios were evaluated by reacting the redox systems with 13CO and integrating the 13C NMR spectra. The results show differences in the intrinsic oxidation-reduction potentials of the chains in hemoglobin tetramer, E1/2(beta)being higher than E1/2(alpha)in neutral solution but not at pH9 and above. The binding of inositol hexakisphosphate does not modify the difference between beta and alpha though substantially increasing the overall potential The results are discussed in the light of current hypotheses to account for the change of Hill coefficient with pH for the reaction studied. The non-equivalence of chains is shown also for heme transfer from methemoglobin. For the phosphate-free protein, the beta chains lose heme more rapidly than that alpha chains; the addition of inositol hexakisphosphate results in the decrease of overall heme transfer as well as of chain heterogeneity.

Binding Sites↗
PubMed1999

Relationship between tyrosinase inhibitory action and oxidation-reduction potential of cosmetic whitening ingredients and phenol derivatives.

The oxidation-reduction potentials of cosmetic raw materials, showing tyrosinase inhibitory action, and phenolic compounds structurally similar to L-tyrosine were determined by cyclic voltammetry. The voltammograms obtained could be classified into 4 patterns (patterns 1-4). Pattern 1, characterized by oxidation and reduction peaks as a pair, was observed with catechol, hydroquinone or phenol, and pattern 2 exhibiting another oxidation peak in addition to oxidation and reduction peaks as a pair was found with arbutin, kojic acid, resorcinol, methyl p-hydroxybenzoate and L-tyrosine as the substrate of tyrosinase. Pattern 3 with an independent oxidation peak only was expressed by L-ascorbic acid, and pattern 4 with a reduction peak only at high potentials, by hinokitiol. The tyrosinase inhibitory activity of these compounds was also evaluated using the 50% inhibitory concentration (IC50) and the inhibition constant (Ki) as parameters. Hinokitiol, classified as pattern 4, showed the highest inhibitory activity (lowest IC50 and Ki). Hydroquinone showing the second highest activity belonged to pattern 1, which also included compounds showing no inhibition of tyrosinase activity. The inhibitory activity of compounds exhibiting pattern 2 was relatively low with Ki values being in the order of 10(-4) M. Although there was no consistent relationship between oxidation-reduction potentials and tyrosinase inhibitory action, the voltammetry data can be used as an additional index to establish the relationship between the structure and the tyrosine inhibitory activity.

Cosmetics↗
PubMed1976

Light-induced oxidation-reduction reactions of cytochromes in the green sulfur photosynthetic bacterium Prosthecochloris aesturarii.

The light-induced oxidation-reduction reactions of cytochromes in intact cells, starved cells, and chlorobium vesicle fractions of the green sulfur photosynthetic bacterium Prosthecochloris aesturarii were studied under anaerobic conditions. On the basis of both kinetic and spectral properties, at least three cytochrome species were found to be involved in the light-induced oxidation-reduction reactions of intact cells. These cytochromes were designated according to the positions of alpha-band maxima as C555 (rapid and slow components) and C552 (intermediate). By comparing the light-minus-dark difference spectra with the reduced-minus-oxidized difference spectra of purified cytochromes of this organism, rapid component C555 and intermediate component C552 are suggested to correspond to the purified cytochromes c-555(550) and c-551.5, respectively. Although the identity of the slow-phase component is uncertain, one possibility is that the slow phase is due to the bound form of c-555(550). In substrate-depleted (starved) cells, only one cytochrome species, C555 remained in the reduced state in the dark and oxidized upon actinic illumination. This corresponds to the rapid C555 component in intact cells. In the case of chlorobium vesicle fractions, one cytochrome species having an alpha-band maximum at 554 nm was oxidized by actinic light. The effects of several inhibitors on the absorbance changes of intact cells were studied. Antimycin A decreased the rate of the dark reduction of rapid C555 component. The complex effects of CCCP (carbonyl cyanide m-chlorophenylhydrazone) on the oxidation-reduction reactions of cytochromes were interpreted as the results of inhibition of the electron donation to oxidized C552 and C555 (slow), and a shift of the dark steady-state redox levels of cytochromes. Based on these findings, it is suggested that the rapid C555 component is located in a cyclic electron transfer pathway. The other two cytochromes, C552 and C555 (slow), may be located in non-cyclic electron transfer pathways and receive electrons from exogenous substrates such as sodium sulfide. A tentative scheme for the electron transfer system in Prosthecochloris aestuarii is presented and its nature is discussed.

Antimycin A↗
PubMed1980

Effect of Estuarine Sediment pH and Oxidation-Reduction Potential on Microbial Hydrocarbon Degradation.

Microbial mineralization rates of two petroleum hydrocarbons, as affected by pH and oxidation-reduction potential, were determined in a Barataria Bay, Louisiana, sediment using C-labeled hydrocarbons. Hydrocarbon mineralization rates were inferred from the activity of respired CO(2). Sediment pH and oxidation-reduction potential were important factors in governing the population of hydrocarbon-degrading microorganisms in the sediment and subsequent mineralization rates. Highest mineralization rates occurred at pH 8.0, and the lowest occurred at pH 5.0. At all pH levels mineralization decreased with decreasing oxidation-reduction potential (i.e., increasing sediment anaerobiosis). Generally, mineralization rates for octadecane were greater than those for naphthalene. Aerobic microorganisms in the oxidized sediment were more capable of degrading hydrocarbons than anaerobic microorganisms in reduced sediment of the same pH.

Journal Article↗
PubMed1975

The kinetics of flavine oxidation-reduction. II. Metal ion interactions.

The oxidation-reduction reactions of tetraacetylriboflavine in the presence of various metal ions in dimethylformamide have been investigated using the stopped-flow technique under anaerobic conditions. Dismutation kinetics in the presence of redox-inactive dissociated divalent metal ions such as Cd2+, Zn2+, and Fe2+ are typically triphasic. Metal ions act primarily upon an intermediate flavine dimer formed by fast association of flavoquinone and flavohydroquinone, resulting in a parallel formation and neutral and chelated radicals. A competition between metal ions and proton donors, e.g. the neutral flavohydroquinone (FredH3), is observed at the level of this intermediate complex. Small spectral changes occur secondarily as an ill-defined intermediate phase which could correspond to the reorganization of the solvation of radical chelate. The neutral radical is finally chelated at a much slower rate, the yield of total radical formation remaining almost unchanged during this kinetic phase. The oxidation of flavohydroquinone by ferric ions, either dissociated or strongly coordinated within a porphyrin, is complete and proceeds through biphasic kinetics. The first phase (Fred leads to F) is much faster than the second one (F leads to Fox). Dismutation resulting from the transient accumulation of neutral flavosemiquinone competes with the direct oxidation with ferric ions for the completion of the second oxidation step. The relative rate of dismutation is essentially limited by acidic-basic reactions in the absence of an excess of ferrous ion. The kinetic analysis of the direct oxidation reactions favors an outer-sphere mechanism for the electron transfer to the ferric ion, either free or strongly coordinated. The formation of a ferrous radical chelate can result from the dismutation reactions only when the amount of ferric ion initially present is not sufficient for complete oxidation.

Cadmium↗
PubMed1995

Oxidation-reduction reactions of metal ions.

Several metal or metalloid ions exist in multiple oxidation states and can undergo electron transfer reactions that are important in biological and environmental systems. There are endogenous metal ions such as iron, copper, and cobalt that participate in oxidation-reduction reactions with species of oxygen like molecular dioxygen, superoxide, and hydrogen peroxide. These reactions may be modulated by endogenous reducing agents such as glutathione, ascorbate, and tocopherol. The reactions can be described in terms of thermodynamics through the use of standard electrode potentials. A favorable reaction will depend on the concentrations of the reactants and may depend on the pH and/or on the presence of organic ligands that form complexes with the metal or metalloid. Arsenate (As(V)) can react with glutathione in buffered aqueous solutions to produce arsenite (As(III)) and oxidized glutathione. This reaction may be important in the methylation reactions of arsenic. Arsenic species can decrease the red blood cell levels of reduced glutathione, but the products of oxidation and the mechanism of oxidation are more complex than those found in water alone. Chromium (VI) is thought to interact with DNA after first reacting with a reducing agent such as glutathione to form lower oxidation states of chromium. These examples illustrate the importance of oxidation-reduction reactions for toxic metals and metalloids.

Carcinogens, Environmental↗
PubMed1992

Magnetic resonance spectroscopic measurement of cellular thiol reduction-oxidation state.

Chromatographic and magnetic resonance spectroscopic measurements of thiol reduction-oxidation state in chemically constructed samples show close analytical agreement. This result, coupled with the synthesis of new probe molecules allowing greater sensitivity and lower toxicity, supports the development of an NMR method for non-invasive thiol redox measurement, an important variable in the response of tumors to radiation and chemotherapy.

Amifostine↗
PubMed1985

Benzo[a]pyrene dione-benzo[a]pyrene diol oxidation-reduction couples; involvement in DNA damage, cellular toxicity, and carcinogenesis.

Three isomeric quinone metabolites of the environmental carcinogen benzo[a]pyrene undergo reversible, univalent oxidation-reduction cycles involving the corresponding benzo[a]pyrene diols and intermediate semiquinone radicals. Under anaerobic conditions, benzo[a]pyrene 1,6-dione, benzo[a]pyrene 3,6-dione, and benzo[a]pyrene 6,12-dione are readily reduced by mild biological agents such as NADH and glutathione. The benzo[a]pyrene diols, in turn, are very rapidly autooxidized to diones when exposed to air. Substantial amounts of hydrogen peroxide are produced during these autooxidations. The benzo[a]pyrene diol/benzo[a]pyrene dione interconversions proceed by one-electron steps; the corresponding semiquinone radicals were detected as intermediates when the reactions were carried out at high pH. Benzo[a]pyrene diones are electron-acceptor substrates for NADH dehydrogenase. Catalytic amounts of these metabolites, together with this respiratory enzyme, function as cyclic oxidation-reduction couples to link NADH and molecular oxygen in the continuous production of hydrogen peroxide. Benzo[a]pyrene diones induce strand scissions when incubated with T7 DNA. The damage is modified by conditions that indicate that reduced oxygen species propagate the reactions responsible for strand scission. Benzo[a]pyrene diones are cytotoxic at low concentrations to cultured hamster cells. The cytotoxic effect can be substantially reduced by depletion of oxygen from the growth medium and the atmosphere in which the cells are incubated. The results support the hypothesis that the biological activity of benzo[a]pyrene diones is due to the regenerative oxidation-reduction cycles involving quinone and hydroquinone forms; activated oxygen species and semiquinone radicals formed during these cycles are most likely responsible for the observed cytotoxic action. The role of activated oxygen species in carcinogenesis is discussed.

Animals↗
PubMed1990

Prognostic implications of postoperative suppression of arterial ketone body ratio: time factor involved in the suppression of hepatic mitochondrial oxidation-reduction state.

To determine the tolerance limit of the liver in the critically suppressed mitochondrial oxidation-reduction state, the arterial ketone body ratio (acetoacetate/3-hydroxybutyrate), which reflects hepatic mitochondrial oxidation-reduction potential, was measured 1319 times in 161 patients during the postoperative critical period. Because patients who showed arterial ketone body ratios between 0.40 and 0.25 had a higher incidence of postoperative complications than had those who showed ratios above 0.40, this was designated as the critical zone of the arterial ketone body ratio. When duration in the critical zone was less than 2 days, 90% of the patients were able to tolerate the condition and survive. By contrast, when an arterial ketone body ratio below 0.40 was prolonged for more than 5 days, there was a high incidence of multiple organ failure and a 100% mortality rate, with the average survival period after a 5-day suppression being estimated as 5.7 +/- 2.4 days. It is suggested that the arterial ketone body ratio in the critical zone must be returned to normal values within 2 days to obtain a good prognosis.

Adolescent↗