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PubMed1992

The effect of shock on blood oxidation-reduction potential.

Oxidation-reduction (redox) potential measurements were made in the blood of rabbits subjected to hemorrhagic shock followed by treatment with a mild oxidizing agent (albumin). Control redox potential reading corrected for pH was -8.8 +/- 1.3 millivolts (mV) in arterial blood (A) and -18.0 +/- 2.0 mV in venous blood (V). This A-V difference indicated that hydrogen equivalents coming from muscle and other tissues were partially consumed in the lungs. A 20-mV drop on the V and a 13 mV on the A side was seen after shock. This did not fully return to control 2 h after return of the shed blood. Infusion of 2 g of albumin/kg/h raised the V redox potential to control, but it returned to untreated levels when the albumin was discontinued. The reductive load imposed on the animal by shock appeared to be large and not readily reversed by reperfusion or by the quantity of albumin given. Thus, it may be concluded that cellular respiration had not been adequately restored. This reductive load may impede recovery by suppression of cellular respiration and other cell and organ functions.

Animals↗
PubMed2005

Synthesis, characterization, and electrochemistry of biorelevant photosensitive low-potential orthometalated ruthenium complexes.

Redox potentials of photosensitive cyclometalated RuII derivatives of 2-phenylpyridine or 2-(4-tolyl)pyridine are controllably decreased by up to 0.8 V within several minutes. This is achieved by irradiation of the ruthena(II)cycles cis-[Ru(o-X-2-py)(LL)(MeCN)2]PF6 (2, X = C6H4 (a) or 4-MeC6H3 (b), LL = 1,10-phenanthroline or 2,2'-bipyridine). The cis geometry of the MeCN ligands has been confirmed by the X-ray structural studies. The sigma-bound sp2 carbon of the metalated ring is trans to LL nitrogen. Complexes 2 are made from [Ru(o-X-2-py)(MeCN)4]PF6 (1) and LL. This "trivial" ligand substitution is unusual because 1a reacts readily with phen in MeCN as solvent to give cis-[Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (2c) in a 83% yield, but bpy does not afford the bpy-containing 2 under the same conditions. cis-[Ru(o-C6H4-2-py)(bpy)(MeCN)2]PF6 (2e) has been prepared in CH2Cl2 (74%). Studies of complexes 2c,e by cyclic voltammetry in MeOH in the dark reveal RuII/III quasy-reversible redox features at 573 and 578 mV (vs Ag/AgCl), respectively. A minute irradiation 2c and 2e converts them into new species with redox potentials of -230 and 270 mV, respectively. An exceptional potential drop for 2c is accounted for in terms of a photosubstitution of both MeCN ligands by methanol. ESR, 1H NMR, and UV-vis data indicate that the primary product of photolysis of 2c is an octahedral monomeric low-spin (S = 1/2) RuIII species, presumably cis-[RuIII(o-C6H4-2-py)(phen)(MeOH)2]2+. The primary photoproduct of bpy complex 2e is cis-[RuII(o-C6H4-2-py)(bpy)(MeCN)(MeOH)]+, and this accounts for a lower decrease in the redox potential. Irradiation of 2c in the presence of added chloride affords [(phen)(o-C6H4-2-py)ClRuIIIORuIVCl(o-C6H4-2-py)(phen)]PF6, a first mu-oxo-bridged mixed valent dimer with a cyclometalated unit. The structure of the dimer has been established by X-ray crystallography.

Journal Article↗
PubMed1975

Identification of cytochrome a and a3 in yeast cells.

1) Cells of Saccharomyces cerevisiae have been analysed by single and double-bean spectroscopy. Evidence is given for two components of cytochrome c oxidase in the alpha-region of their absorption spectrum. A rapidly reduceable component with a maximum at 600 nm and a slowly reduceable component with a maximum at 604 nm contribute about equal amounts to the total alpha-absorption of cytochrome c oxidase. 2) The component absorbing at 600 nm was identified as the high-potential component with a redox potential of 340 - 355mV, and the 604-nm component as the low-potential component of cytochrome c oxidase with redox potential of 180 - 190 mV. 3) Both components can be characterized by analysing the reduction kinetics in the presence of carbon monoxide. In the presence of saturating concentrations of carbon monoxide, an oxygen pulse leads to a rapid oxidation and subsequent reduction of cytochrome c oxidase, but the rapid reduction phase at 600 nm completely disappears, demonstrating its identity with cytochrome a3, which, being liganded by carbon monoxide in its reduced state, cannot react any more. The component which becomes oxidized and later reduced in the presence of carbon monoxide -- by definition cytochrome a -- has an absorption maximum at 604 nm. 4) The total extinction change at 604 nm in the presence of carbon monoxide is nearly as high as in its absence, but the reduction occurs in two phases and only the second phase, which contributes 50 - 60% to the total absorbance, corresponds in redox potential and kinetic properties to cytochrome a. Because the redox potential of the first reduction phase is very close to that of the low-potential copper atom of cytochrome c oxidase, it is concluded that the apparent increase in the extinction coefficient of cytochrome a in the presence of carbon monoxide is the result of a strong interaction between the ligand fields of cytochrome a and copper, induced by the binding of carbon monoxide to reduced cytochrome a3.

Carbon Monoxide↗
PubMed1994

The relationship between phosphorylation potential and redox state in the isolated working rabbit heart.

The effects of the cytosolic and mitochondrial redox state on the function and phosphorylation potential of working perfused rabbit hearts were studied. Hearts were perfused with glucose, while lactate, aminooxy-acetate (an inhibitor of the malate-aspartate shuttle), beta-hydroxybutyrate, and pyruvate were sequentially added to the perfusate to manipulate the cytosolic and mitochondrial NAD+/NADH ratio. The phosphorylation potential and product of ADP and P(i) were both found to be proportional to mitochondrial redox state. There was no overall relationship between cytosolic redox potential and the ATP/ADP x P(i) ratio, although at high mitochondrial NADH, there was a tendency for the states with more reduced cytoplasm to be associated with a lower phosphorylation potential. Cardiac output and dP/dt were decreased after 75 microM aminooxy-acetate was present for 15 min, and remained low when 0.5-1.0 mM beta-hydroxybutyrate was added, even though the beta-hydroxybutyrate period was characterized by both very low cytosolic NAD+/NADH and high mitochondrial NADH. Function returned to normal when the cytoplasm was oxidized by addition of 10 mM pyruvate, and although MVO2 rose from 4.0 +/- 0.4 to 5.0 +/- 0.5, this was not accompanied by statistical changes in either mitochondrial NADH or phosphorylation potential. Therefore, the cytosolic redox state may play a role in cardiac function, but has only a minor contribution to the regulation of the phosphorylation potential in the working perfused rabbit heart.

Animals↗
PubMed1986

The vitamin C treatment of allergy and the normally unprimed state of antibodies.

I previously described that bowel tolerance (the amount that almost causes diarrhea) to oral ascorbic acid, increases in a person somewhat proportionally to the "toxicity" of his disease. Ascorbic acid ameliorates symptoms and sometimes cures certain diseases at high threshold levels near bowel tolerance. High concentrations of ascorbate cause the redox potential of the redox couple (ascorbate/dehydroascorbate, AA/DHA) to become reducing in diseased tissues. Allergic and sensitivity reactions are frequently ameliorated and sometimes completely blocked by massive doses of ascorbate. I now hypothesize that one mechanism in blocking of allergic symptoms is the reducing of the disulfide bonds between the chains in antibody molecules making their bonding antigen impossible. I further hypothesize that antibodies seek to match antigens only in areas where stray free radicals or a relatively oxidizing redox potential exists. The redox state of normal, healthy tissue does not allow for the bonding of antibodies to antigen. When antioxidant, free radical scavenging systems are overwhelmed, inflammatory, hypersensitivity, and "autoimmune" conditions may result.

Animals↗
PubMed2002

Acetoacetate augments beta-adrenergic inotropism of stunned myocardium by an antioxidant mechanism.

Blunted beta-adrenergic inotropism in stunned myocardium is restored by pharmacological (N-acetylcysteine) and metabolic (pyruvate) antioxidants. The ketone body acetoacetate is a natural myocardial fuel and antioxidant that improves contractile function of prooxidant-injured myocardium. The impact of acetoacetate on postischemic cardiac function and beta-adrenergic signaling has never been reported. To test the hypothesis that acetoacetate restores contractile performance and beta-adrenergic inotropism of stunned myocardium, postischemic Krebs-Henseleit-perfused guinea pig hearts were treated with 5 mM acetoacetate and/or 2 nM isoproterenol at 15-45 and 30-45 min of reperfusion, respectively, while cardiac power was monitored. The myocardium was snap frozen, and its energy state was assessed from phosphocreatine phosphorylation potential. Antioxidant defenses were assessed from GSH/GSSG and NADPH/NADP(+) redox potentials. Stunning lowered cardiac power and GSH redox potential by 90 and 70%, respectively. Given separately, acetoacetate and isoproterenol each increased power and GSH redox potential three- to fivefold. Phosphocreatine potential was 70% higher in acetoacetate- vs. isoproterenol-treated hearts (P < 0.01). In combination, acetoacetate and isoproterenol synergistically increased power and GSH redox potential 16- and 7-fold, respectively, doubled NADPH redox potential, and increased cAMP content 30%. The combination increased cardiac power four- to sixfold vs. the individual treatments without a coincident increase in phosphorylation potential. Potentiation of isoproterenol's inotropic actions endured even after acetoacetate was discontinued and GSH potential waned, indicating that temporary enhancement of redox potential persistently restored beta-adrenergic mechanisms. Thus acetoacetate increased contractile performance and potentiated beta-adrenergic inotropism in stunned myocardium without increasing energy reserves, suggesting its antioxidant character is central to its beneficial actions.

Acetoacetates↗
PubMed1979

Redox potential-dependent nitrite metabolism by Salmonella typhimurium.

Salmonellae are generally resistant to the inhibitory effects of NaNO2. Removal of the lipopolysaccharide of Salmonella typhimurium by ethylenediaminetetraacetic acid pretreatment did not result in subsequent inhibtion of growth by NaNO2, indicating that lipopolysaccharide does not function to exclude NaNO2 from the cell. NaNO2 disappeared from the medium while the cells were growing, but, after stationary phase was reached, no further losses were observed unless the pH was maintained above 7.0. Similar losses were observed in a cell-free system if the redox potential of the medium was between -250 and -175 mV. If the disrupted cell suspension was first heated in a boiling water bath for 15 to 18 min, no NaNO2 loss was observed regardless of the redox potential. S. typhimurium is capable of metabolizing NaNO2, possibly by means of a nitrite-reducing enzyme function which is redox controlled.

Drug Resistance, Microbial↗
PubMedDate not supplied

[Changes in the oxidation-reduction potential of the rat brain during nembutal anesthesia].

The effect of the pentobarbital anaesthesia (40 mg/kg) on the potential of the cortical redox state (E) recorded by implanted platinum electrode was studied in male albino rats. A gradual decrease in the breathing frequency induced by pentobarbital was accompanied by a gradual reduction of the redox potential by 30-80 mV. During the episodes with intermittent breathing there were additional decreases in redox potential by 30-80 mV against the background of which some rhythmical oscillations could be observed (the amplitude up to 25-30 mV, periods in 5-15 sec). The obtained data suggest that pentobarbital anaesthesia heavily changes the redox state of the brain tissue and shifts the balance to reducing state. Oscillations in redox potential against the background of breathing interruptions seem to be the typical glycolytic oscillations.

Anesthesia Recovery Period↗
PubMed2000

Regulation of dinitrogenase reductase ADP-ribosyltransferase and dinitrogenase reductase-activating glycohydrolase by a redox-dependent conformational change of nitrogenase Fe protein.

The nitrogenase-regulating enzymes dinitrogenase reductase ADP-ribosyltransferase (DRAT) and dinitrogenase reductase-activating glycohydrolase (DRAG), from Rhodospirillum rubrum, were shown to be sensitive to the redox status of the [Fe(4)S(4)](1+/2+) cluster of nitrogenase Fe protein from R. rubrum or Azotobacter vinelandii. DRAG had <2% activity with oxidized R. rubrum Fe protein relative to activity with reduced Fe protein. The activity of DRAG with oxygen-denatured Fe protein or a low molecular weight substrate, N(alpha)-dansyl-N(omega)-(1,N(6)-etheno-ADP-ribosyl)-arginine methyl ester, was independent of redox potential. The redox midpoint potential of DRAG activation of Fe protein was -430 mV versus standard hydrogen electrode, coinciding with the midpoint potential of the [Fe(4)S(4)] cluster from R. rubrum Fe protein. DRAT was found to have a specificity opposite that of DRAG, exhibiting low (<20%) activity with 87% reduced R. rubrum Fe protein relative to activity with fully oxidized Fe protein. A mutant of R. rubrum in which the rate of oxidation of Fe protein was substantially decreased had a markedly slower rate of ADP-ribosylation in vivo in response to 10 mM NH(4)Cl or darkness stimulus. It is concluded that the redox state of Fe protein plays a significant role in regulation of the activities of DRAT and DRAG in vivo.

ADP Ribose Transferases↗
PubMed1984

Redox potential-pH properties of the flavoprotein L-amino-acid oxidase.

The redox potential-pH characteristics of the enzyme L-amino-acid oxidase (L-amino-acid: oxygen oxidoreductase (deaminating), EC 1.4.3.2) have been measured in the pH range 6.2 to 8.3 at 4 degrees C. All potentials are reported versus the standard hydrogen electrode. Consistent with the protonation states proposed for the anionic red semiquinone and anionic dihydroquinone forms of the flavin coenzyme, the first electron potential is independent of pH (-0.056 +/- 0.006 V), while the second electron transfer potential is pH-dependent, exhibiting a 0.060 V/pH unit slope. At all pH values investigated, the percentage of semiquinone species observed matches closely that calculated from measured potential separations. The semiquinone species is thermodynamically stable, as indicated by formation of semiquinone, similarity of redox potentials in oxidative and reductive directions, and by the slope of Nernst plots.

Amino Acid Oxidoreductases↗
PubMed2005

Redox equilibria in hydroxylamine oxidoreductase. Electrostatic control of electron redistribution in multielectron oxidative processes.

We report results of continuum electrostatics calculations of the cofactor redox potentials, and of the titratable group pK(a) values, in hydroxylamine oxidoreductase (HAO). A picture of a sophisticated multicomponent control of electron flow in the protein emerged from the studies. First, we found that neighboring heme cofactors strongly interact electrostatically, with energies of 50-100 mV. Thus, cofactor redox potentials depend on the oxidation state of other cofactors, and cofactor redox potentials in the active (partially oxidized) enzyme differ substantially from the values obtained in electrochemical redox titration experiments. We found that, together, solvent-exposed heme 1 (having a large negative redox potential) and heme 2 (having a large positive redox potential) form a lock for electrons generated during the oxidation reaction The attachment of HAO's physiological electron transfer partner cytochrome c(554) results in a positive shift in the redox potential of heme 1, and "opens the electron gate". Electrons generated as a result of hydroxylamine oxidation travel to heme 3 and heme 8, which have redox potentials close to 0 mV versus NHE (this result is in partial disagreement with an existing experimental redox potential assignment). The closeness of hemes 3 and 8 from different enzyme subunits allows redistribution of the four electrons generated as a result of hydroxylamine oxidation, among the three enzyme subunits. For the multielectron oxidation process to be maximally efficient, the redox potentials of the electron-accepting cofactors should be roughly equal, and electrostatic interactions between extra electrons on these cofactors should be minimal. The redox potential assignments presented in the paper satisfy this general rule.

Bacterial Proteins↗
PubMed1993

Redox regulation of energy transfer efficiency in antennas of green photosynthetic bacteria.

The efficiency of energy transfer from the peripheral chlorosome antenna structure to the membrane-bound antenna in green sulfur bacteria depends strongly on the redox potential of the medium. The fluorescence spectra and lifetimes indicate that efficient quenching pathways are induced in the chlorosome at high redox potential. The midpoint redox potential for the induction of this effect in isolated chlorosomes from Chlorobium vibrioforme is -146 mV at pH 7 (vs the normal hydrogen electrode), and the observed midpoint potential (n = 1) decreases by 60 mV per pH unit over the pH range 7-10. Extraction of isolated chlorosomes with hexane has little effect on the redox-induced quenching, indicating that the component(s) responsible for this effect are bound and not readily extractable. We have purified and partially characterized the trimeric water-soluble bacteriochlorophyll a-containing protein from the thermophilic green sulfur bacterium Chlorobium tepidum. This protein is located between the chlorosome and the membrane. Fluorescence spectra of the purified protein indicate that it also contains groups that quench excitations at high redox potential. The results indicate that the energy transfer pathway in green sulfur bacteria is regulated by redox potential. This regulation appears to operate in at least two distinct places in the energy transfer pathway, the oligomeric pigments in the interior of the chlorosome and in the bacteriochlorophyll a protein. The regulatory effect may serve to protect the cell against superoxide-induced damage when oxygen is present. By quenching excitations before they reach the reaction center, reduction and subsequent autooxidation of the low potential electron acceptors found in these organisms is avoided.

Bacteria, Anaerobic↗
PubMed1986

On the capacity of nitroheterocyclic compounds to elicit an unusual axial asymmetry in cultured rat embryos.

A series of nitroheterocyclic compounds with antimicrobial and radiosensitizing properties was tested for embryotoxicity in cultured Sprague-Dawley rat embryos, and their effects were compared with various other five-membered heterocycles. Nifuroxime, furazolidone, nitrofurazone, niridazole, 2-nitroimidazole, and ronidazole each elicited a striking malformation characterized by asymmetrical, right-sided hypoplasia when coincubated with embryos for 26 hr. Minimum concentrations required to elicit this unusual defect ranged from 0.01 mM with nifuroxime and furazolidone to 0.5 mM with ronidazole and were roughly correlated with single electron redox potentials; i.e., agents with relatively high redox potentials were generally more effective than those with low potentials. Nitrofurantoin failed to elicit this unusual malformation but exhibited an extremely steep dose-response curve for embryolethality. Metronidazole and 4-nitroimidazole, nitroheterocyclic agents with relatively low redox potentials, did not produce the asymmetric abnormality nor were they highly embryotoxic, even at concentrations up to 2 mM. 2-Amino-5-nitrothiazole and 4'-methylniridazole also failed to evoke the asymmetric malformation but produced significant embryotoxicity as manifested by decreased growth parameters and elicitation of other kinds of malformations. Heterocyclic compounds not bearing a nitro group (furosemide, 2-aminothiazole, and 2-aminoimidazole) failed to elicit axial asymmetry at concentrations up to 1.0 mM but produced other signs of embryotoxicity at the highest concentrations tested. The results suggest that the presence of a reducible nitro group is critical for generation of the unusual malformation and that the single-electron redox potential of the nitro group plays a dominant but not exclusive role in the capacity of these chemicals to evoke axial asymmetry in cultured rat embryos.

Abnormalities, Drug-Induced↗
PubMed2006

Measurement of the concentration of Mn2+ and Mn3+ in the manganese-catalyzed 1,4-cyclohexanedione-acid-bromate reaction using redox-triggered magnetic resonance spectroscopy.

A new nuclear magnetic resonance (NMR) experiment is reported, where the spectrometer is triggered using the output from a combination redox electrode. This technique was used to probe redox oscillations in the 1,4-cyclohexanedione-acid-bromate reaction. Manganese(III) acetate or manganese(II) sulfate was used as the catalyst, and the periodic change in concentration of Mn2+/Mn3+ ions was determined as a function of redox potential. The concentration of Mn3+ ions was at a maximum at high redox potential and at a minimum at low redox potential. Also, redox potentials were found to not be dominated by the Mn2+/Mn3+ couple.

Journal Article↗
PubMed2005

One-electron reduction potential for oxygen- and sulfur-centered organic radicals in protic and aprotic solvents.

We estimated one-electron reduction potentials of redox-active organic molecules for a spectrum of eight different functional groups (phenoxyl, p-benzoquinone, phenylthiyl, p-benzodithiyl, carboxyl, benzoyloxyl, carbthiyl, and benzoylthiyl) in protic (water) and aprotic (acetonitrile, N,N-dimethylacetamide) solvents. Electron affinities (EA) were evaluated in a vacuum with high level quantum chemical methods using Gaussian3-MP2 (G3MP2) and Becke 3 Lee, Yang, and Parr functional B3LYP with aug-cc-pVTZ basis set. To evaluate one-electron redox potentials, gas-phase free energies were combined with solvation energies obtained in a two-step computational approach. First, atomic partial charges were determined in a vacuum by the quantum chemical method B3LYP/6-31G(d,p). Second, solvation energies were determined, solving the Poisson equation with these atomic partial charges. Redox potentials computed this way, compared to experimental data for the 21 considered organic compounds in different solvents, yielded overall root-mean-square deviations of 0.058 and 0.131 V using G3MP2 or B3LYP to compute electronic energies, respectively, while B3LYP/6-31G(d,p) was used to compute solvation energies.

Journal Article↗
PubMed1985

Optimal redox electrode potential for 24-hour rabbit kidney perfusion.

This study was conducted to determine whether an optimum redox electrode potential existed for 24-hr hypothermic perfusion of rabbit kidneys. The perfusate consisted of a Ringer's-albumin solution to which was added varying amounts of the reducing agents, glutathione and ascorbate, either individually or in equimolar amounts. Electrode potential was monitored with a vitreous carbon electrode in relation to a silver-silver chloride reference cell, and kidney function was measured after preservation by connection to the circulation of a perfusor animal via a shunt. The best results were obtained using equimolar amounts of the reducing agents. Under these circumstances a definite optimum range for perfusate electrode potential was identified (Es = 40-70 mV) within which renal function was indistinguishable from unpreserved controls. Higher and lower perfusate electrode potentials were associated with significantly lower creatinine clearances. However, the explanation for these results appeared to be more complex than redox control alone, since kidney function was dependent not only on the redox potential of the perfusate but also on the reducing agents with which the adjustment had been made. Ascorbate proved to be significantly better than glutathione within the optimum potential range.

Animals↗
PubMed1987

Redox chemistry of the 9-anilinoacridine class of antitumor agents.

9-Anilinoacridines bearing a 1'-NHR substituent on the anilino ring undergo facile, chemically reversible, two-electron oxidation to quinone diimines. The chemical and electrochemical oxidation of three groups of 9-anilinoacridines (1'-substituted derivatives, together with 3'-substituted analogues and acridine-substituted analogues of the clinical antileukemic drug amsacrine) have been studied and their redox potentials determined. For aniline-substituted derivatives, redox potentials (E1/2) correlate well with substituent electronic properties, with electron-donating substituents facilitating oxidation. Substituents in the acridine ring have little effect on redox potentials, indicating minimal transmission of electronic effects from the acridine to the aniline rings. Although the broad class of 9-anilinoacridines show biological activity over a very wide range of structural variations, a 1'-NHR substituent is a common feature of the most active derivatives. Nevertheless, no clear quantitative relationships between redox potential and biological activity could be discerned, and the relevance of this redox chemistry to the mode of action of amsacrine and other 9-anilinoacridines remains unclear.

Aminoacridines↗
PubMedDate not supplied

[Redox regulation in ATP synthesis].

Evidence is considered which points to changes of redox potential of the redox-centres in mitochondria during energization, to high sensitivity of ATP-synthetase to redox agents. Examples of ATP-syntheses in model systems stimulated with an electron are discussed. This stimulation is so efficient that it permits weakening of the bond between phosphorus atom and extremely bad leaving group O- in inorganic phosphate-phosphorylating agent in ATP synthesis during oxidative phosphorylation. The sum of these data suggests that function of the redox-centres found in the coupling site may be the accumulation of the intermediate inducing ADP and Phinorg interactions. The electron pool may serve as an intermediate. Thus the redoxcentre function in the coupling site accepting and accumulating the electrons during energization may be compared with chlorophyll function in photosynthesis. Change of redox potential of redox-centres at energization (by protonation, for example) initiates electron transfer in ATP-synthetase, which by the formation of highly reactive-free radical of ADP provides the occurrence of endergonic reaction of ATP synthesis, i.e. storage of energy as a chemical bond.

Adenosine Triphosphatases↗