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PubMed1979

Potentiometric titrations and oxidation-reduction potentials of manganese and copper-zinc superoxide dismutases.

Bovine erythrocyte superoxide dismutase and two manganese-containing superoxide dismutases have been reduced by the indirect coulometric titration method with methylviologen as the mediator-titrant. On the basis of the titration data the manganese-containing superoxide dismutases contain 1 g-atom of metal per mol of enzyme (dimer). E0' = +0.31 V for the enzyme from Escherichia coli which exhibits a complicated pH dependence above neutral pH. The Bacillus stearothermophilus manganese-containing enzyme has an E0' = +0.26 V and delta Em/pH is 50 mV. Bovine erythrocyte superoxide dismutase exhibits anomalous behavior in the coulometric titration curves, which is indicative of two nonequivalent copper centers in the enzyme. Addition K3Fe(CN)6 or K2IrCl6 to the enzyme solution, prior to coulometric titration, indicates that these anions bind preferentially to one of the copper centers.

Animals↗
PubMed1989

Oxidation-reduction and the molecular mechanism of a regulatory RNA-protein interaction.

Iron-responsive elements (IREs) are RNA motifs that have been identified within the 5' untranslated region of ferritin messenger RNA and the 3' untranslated region of transferrin receptor mRNA. A single IRE mediates iron-dependent control of ferritin translation, whereas multiple IREs are found in the region of the transferrin receptor mRNA responsible for iron-dependent control of mRNA stability. A cytosolic protein binds in vitro to the IREs of both mRNAs. The IRE-binding protein (IRE-BP) is shown to require free sulfhydryl groups for its specific interaction with the IRE. Treatment of lysates with reducing agents increases the binding activity, whereas agents that block sulfhydryls inhibit binding. Iron starvation, leading to decreased ferritin translation, results in increased binding activity, which is explained by an increase in the fraction of the IRE-BP that is in a fully reduced state.

Cytosol↗
PubMedDate not supplied

In vitro studies of iron bioavailability. Probing the concentration and oxidation-reduction of pinto bean iron with ferrous chromogens.

The bioavailability of iron from foods is ultimately determined by interactions between iron and other components in the digestive milieu. Perhaps the most important factor is the concentration of Fe2+ during transit through the duodenum. During in vitro simulations of human digestion it is possible to probe the concentration of Fe2+, the rate of Fe2+ formation, and total iron concentration using ferrous chromogens. It is crucial, of course, that the chromogen not interfere with the redox reactions occurring during digestion. Accordingly, ferrozine was examined with regard to its ability to reduce complexes Fe3+, alter rates of Fe3+ production, detect Fe2+ present in the digestive mixture and differentiate the effects of chelating and reducing agents in the mobilization of iron from pinto beans. The chromogen was found to be free from apparent artefacts and to be a sensitive and reproducible probe of the state of iron in digestive mixtures.

Biological Availability↗
PubMed1987

Oxidation-reduction reactions of iron bleomycin in the absence and presence of DNA.

Using the pulse radiolysis technique, we have demonstrated that bleomycin-Fe(III) is stoichiometrically reduced by CO2- to bleomycin-Fe(II) with a rate of (1.9 +/- 0.2) x 10(8) M-1s-1. In the presence of calf thymus DNA, the reduction proceeds through free bleomycin-Fe(III) and the binding constant of bleomycin-Fe(III) to DNA has been determined to be (3.8 +/- 0.5) x 10(4) M-1. It has also been demonstrated that in the absence of DNA O2- reacts with bleomycin-Fe(III) to yield bleomycin-Fe(II)O2, which is in rapid equilibrium with molecular oxygen, and decomposes at room temperature with a rate of (700 +/- 200) s-1. The resulting product of the decomposition reaction is Fe(III) which is bound to a modified bleomycin molecule. We have demonstrated that during the reaction of bleomycin-Fe(II) with O2, modification or self-destruction of the drug occurs, while in the presence of DNA no destruction occurs, possibly because the reaction causes degradation of DNA.

Bleomycin↗
PubMed1999

Natural engineering principles of electron tunnelling in biological oxidation-reduction.

We have surveyed proteins with known atomic structure whose function involves electron transfer; in these, electrons can travel up to 14 A between redox centres through the protein medium. Transfer over longer distances always involves a chain of cofactors. This redox centre proximity alone is sufficient to allow tunnelling of electrons at rates far faster than the substrate redox reactions it supports. Consequently, there has been no necessity for proteins to evolve optimized routes between redox centres. Instead, simple geometry enables rapid tunnelling to high-energy intermediate states. This greatly simplifies any analysis of redox protein mechanisms and challenges the need to postulate mechanisms of superexchange through redox centres or the maintenance of charge neutrality when investigating electron-transfer reactions. Such tunnelling also allows sequential electron transfer in catalytic sites to surmount radical transition states without involving the movement of hydride ions, as is generally assumed. The 14 A or less spacing of redox centres provides highly robust engineering for electron transfer, and may reflect selection against designs that have proved more vulnerable to mutations during the course of evolution.

Biological Evolution↗
PubMed1983

[Differences in the action of antimycin and 2-nonyl-4-hydroxyquinoline N-oxide on oxidation-reduction of mitochondrial cytochromes b].

The differences in the effects of two similar electron transfer inhibitors, antimycin and 2-nonyl-4-hydroxyquinoline N-oxide (HOQNO) on the reactions of cytochromes b are described. In the cyanide-inhibited submitochondrial particles of bovine heart, HOQNO strongly stimulates cytochrome b reduction by ascorbate in the presence of redox mediators, e. g. N,N,N',N'-tetramethylparaphenylene diamine, 2,6-dichlorophenolindophenol, diaminodurol and phenazine methosulfate; this effect can be reversed by antimycin. Addition of both inhibitors to the submitochondrial particles aerobically equilibrated with succinate/fumarate redox buffer at E = +54 mV in the presence of cyanide results in a similar reduction of cytochromes b, which in the case of antimycin is readily reversed by phenazine methosulfate but is resistant to this redox mediator in the presence of HOQNO. The latter causes additional reduction of cytochrome b562 in the argone atmosphere, the effect being reversed by antimycin. In the presence of HOQNO the anaerobic redox titration curve of cytochrome b562 is shifted towards a high potential region by 20-30 mV. An additional reduction of cytochromes b induced by HOQNO can be due to superposition of two effects, i. e. extra-reduction of cytochromes b566 and b562 requiring O2 and a true positive shift of E0 of cytochrome b562.

Animals↗
PubMed1990

Oxidation-reduction potentials of flavin and Mo-pterin centers in assimilatory nitrate reductase: variation with pH.

Potentiometric titrations of assimilatory nitrate reductase from Chlorella vulgaris were performed within the pH range 6.0-9.0. Mo(V) was measured by room temperature EPR spectroscopy while the reduction state of FAD was monitored by CD spectroscopy. Between pH 6 and 8.5, the line shape of the Mo(V) EPR signal was constant, exhibiting superhyperfine coupling to a single, exchangeable proton. Potentiometric titrations indicated the Em values for the Mo(VI)/Mo(V) (+61 mV, pH 6) and Mo(V)/Mo(IV) (+35 mV, pH 6) couples decreased with increasing pH by approximately -59 mV/pH unit, consistent with the uptake of a single proton upon reduction of Mo(VI) to Mo(V) and Mo(V) to Mo(IV). The pKa values for the dissociation of these redox-coupled protons appeared to lie outside the pH range studied: pKo(MoVI), pKo(MoV) less than 5.5; pKr(MoV), pKr(MoIV) greater than 9. The Em (n = 2) for FAD (-250 mV, pH 7) varied by approximately -30 mV/pH unit within the pH range 6.0-9.0. Low-temperature EPR potentiometry at the extreme pH values indicated less than 0.5% conversion of FAD to the semiquinone form at the midpoint of the titrations. In contrast, NADH-reduced enzyme exhibited approximately 3-5% of the FAD in the semiquinone form, present as the anionic (FAD.-) species, the spectrum characterized by a line width of 1.3 mT at both pH 6.0 and 9.0.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlorella↗
PubMed1978

Oxidation-reduction potential measurements of cytochrome c peroxidase and pH dependent spectral transitions in the ferrous enzyme.

The redox potential of the ferrous/ferric couple in cytochrome c peroxidase has been measured as a function of pH between pH 4.5 and 8. The redox potential decreases linearly as a function of pH between pH 4.5 and 7 with a slope of --57 +/- 2 mV per pH unit. Above pH 7, there is a positive inflection in the midpoint potential versus pH plot attributed to an ionizable group in the ferrous enzyme with pKa of 7.6 +/- 0.1. The midpoint potential at pH 7 is--0.194 V relative to the standard hydrogen electrode at 25 degree C. Ferrocytochrome c peroxidase undergoes a reversible spectral transition as a function of pH. Below pH 7, the enzyme has a spectrum typical of high spin ferroheme proteins while above pH 8, the spectrum is typical of low spin ferroheme proteins. The transition is caused by a co-operative, two proton ionization with an apparent pKa of 7.7 +/- 0.2. Two other single proton ionizations cause minor perturbations to the spectrum of ferrocytochrome c peroxidase. One has a pKa of 5.7 +/- 0.2 while the second has a pKa of 9.4 +/- 0.2.

Cytochrome-c Peroxidase↗
PubMedDate not supplied

[Relationship between the oxidation-reduction system of astrocytes with production of active forms of oxygen].

Cells of neuroglia--the astrocytes are of interest from the point of view of their participation in phagocytosis. Phagocyte ability to generate active oxygen forms (AOF) as used as the basic criterion of the estimation of their functional activity. For the purpose to clear up molecular and cellular mechanisms of phagocytosis a study of astrocyte redox-systems, participating in production of AOF, was undertaken. Registration of AOF in astrocytes was carried out using a method of luminol-dependent chemiluminescence. Primary culture of guinea pig astrocytes was used. Spontaneous chemiluminescence of low intensity was found for the astrocytes at the presence of luminol. The destruction of the cells was accompanied by a significant growth of the intensity of spontaneous chemiluminescence. Suspension of endocutosis inductors, particle of latex and phytohemagglutinin, added to astrocytes did not result in formation of AOF, characteristic for other cells, possessing phagocytosis. It was established, that addition of hydrogen peroxide destroys astrocytes at the presence of luminol and gives rise to the emission. Chemiluminescence was not observed in similar experiments with intact cells. A conclusion was made that inside astrocytes there are structures, which show peroxidase-like activity.

Animals↗
PubMedDate not supplied

[Interaction of membrane proton conductivity, membrane and oxidation-reduction potential in Escherichia coli].

It was shown that the proton conductivity of Escherichia coli membranes depends on pH and other conditions of bacterial growth. It is considerably lower in cells fermenting glucose and accomplishing the nitrate-nitrite respiration compared with cells accomplishing the oxygen respiration. Proton conductivity increases substantially with decreasing pH of medium. It was found that proton conductivity is related to the redox and membrane potentials of cells. The energy-dependent flux of protons from cells and the ATPase activity of membrane vesicles considerably vary depending on whether bacteria are grown under aerobic or anaerobic conditions. The H+ flux from cells fermenting glucose (pH 7.5) was 1.7 times greater than the H+ flux from cells that accomplish the nitrate-nitrite and oxygen respiration. The N,N'-dicyclohexylcarbodiimide (DCCD)-sensitive ATPase activity increased 2.5 times as K+ concentration increased to 100 mM (including residual K+ in potassium-free medium). The DCCD-sensitive ATPase activity considerably decreased with decreasing pH of medium, whereas the ATPase activity that was not suppressed by DCCD was stimulated. These results can be used for establishing the relationship between membrane proton conductivity and the energy-dependent H+ flux and ATPase activity.

Adenosine Triphosphatases↗
PubMedDate not supplied

[The modelling of the glycolytic oscillations in the potential of the oxidative-reductive status of the brain tissue in waking and anesthetized rats].

It was found that chemical hypoxia created by intraperitoneal injection of potassium cyanide (5-7 mg/kg) induced in both waking and anaesthetized (pentobarbital, 40 mg/kg) albino rats a significant decrease in the brain redox state potential (E) monitored with platinum electrodes. This decrease could be accompanied by a generation in some brain points of local chains of gradually damped quasisinusoidal E oscillations. Such oscillations were more expressed in waking than in anaesthetized animals. The frequency range of these oscillations was 4-7 cycles/min. This is the range of overlapping frequency ranges characteristic for the high level of vigilance (5-20 cycles/min) and slow-wave sleep and drowsiness (1.5-6 cycles/min). The amplitude of the observed oscillations was close to the maximal amplitude of the brain E oscillations characteristic for the high level of vigilance (up to several mV). The obtained evidence favors our suggestion that behavior-related E oscillations are formed by the oscillations in the redox balance of glycolysis. The similarity of the normal physiological oscillations and those simulated by us under abnormal conditions suggest a certain common mechanism of their generation.

Anesthesia↗
PubMed2001

Polymer modified electrodes for the reversible oxidation-reduction of NAD+/NADH for use within amperometric biosensors.

Electrochemical enzyme based biosensors continue to attract much attention due to the simplified analyses they promise, in comparison to many more complicated analytical procedures. The largest group of enzymes, are those that rely NAD(P)+/NAD(P)H as cofactors. One of the problems associated with the use NAD(P)+/NAD(P)H redox couples, however, within electrochemical biosensors is their ability to passivate noble metal electrodes. There have been many attempts to overcome this problem, such as the use of carbon paste electrodes [1], although approaches such as these are both cumbersome and typically irreproducible. In recent years conducting polymers such as poly(3-methylthiophene) [2] have also been used to modify noble metal electrode surfaces to lower the overpotentials required, while poly(phenol red) has been incorporated into films to offer selectivity against interferents [3,4]. In this study platinum electrodes have been electrochemically coated with mixed polymer films of poly(phenol red) together with poly(3-methylthiophene), poly(aniline) or poly(o-phenylenediamine) to offer enhanced performance. Cyclic voltammetry has been used to compare the electrochemical behaviour of the NAD+/NADH redox couple over repeated potential cycles, with the most favourable results being seen with the poly(aniline)/poly(phenol red) and poly(o-phenylenediamine)/poly(phenol red) coated electrodes.

Biosensing Techniques↗
PubMed1979

Oxidation-reduction potentials of the hemes in cytochrome C3 from Desulfovibrio gigas in the presence and absence of ferredoxin by EPR spectroscopy.

1. Ferricytochrome c3 from D. gigas exhibits two low-spin ferric heme EPR resonances with gz-values at 2.959 and 2.853. Ferrocytochrome c3 is diamagnetic based on the absence of any EPR signals. 2. EPR potentiometric titrations result in the resolution of the two low-spin ferric heme resonances into two additional heme components representing in total the four hemes of the cytochrome, with EM values of -235 mV and -315 mV at heme resonance I and EM values of -235 mV and -306 mV at heme resonance II. 3. EPR spectroscopy has detected a significant diminution of intensity (approx. 60 p. 100) in the gx amplitude of ferricytochrome c3 in the presence of D. gigas ferredoxin II. The presence of ferredoxin II also causes a more negative shift in the EM of the second components of the signals at heme resonances I and II of cytochrome C3. Both observations suggest that an interaction has occurred between cytochrome C3 and ferredoxin II. 4. The results presented suggest that the heme ligand environment of ferricytochrome c3 from D. gigas is less perturbed and/or less asymmetric than environment for ferricytochrome c3 from D. vulgaris whose EPR behavior indicates the non-equivalence of all four hemes.

Cytochrome c Group↗
PubMed1986

Involvement of glutathione oxidation reduction in parathyroid hormone secretion.

This study determines whether calcium affects glutathione metabolism and whether glutathione metabolism may influence parathyroid (PTH) secretion in collagenase dispersed bovine parathyroid cells. Reduced glutathione (GSH) and glutathione disulfide (GSSG) were measured fluorometrically and enzymatically while PTH secretion was determined by radioimmunoassay. The total GSH and GSSG content of parathyroid cells was found to range from 1.59 to 1.71 micrograms/mg cell protein, and this did not vary significantly with changes in extracellular calcium. An increase in the medium calcium concentration from 0.5 to 2.0 mM did, however, cause an increase in GSSG from 0.43-0.54 to 1.19-1.20 micrograms/mg protein with a concomitant decrease in GSH. The compound 2-cyclohexen-1-one was used to deplete the cells of GSH at a low-calcium medium (0.5 mM) to levels seen in high-calcium medium (2.0 mM). This treatment was found to inhibit PTH secretion in the low-calcium medium, as if the cells were incubated in high medium calcium. Both 2-cyclohexen-1-one and calcium caused a rapid decrease in reduced GSH levels and in hormone secretion. The ketone was not found to affect cellular protein synthesis, indicating that there was no nonspecific toxic effect of this treatment on the cells. These results suggest that changes in the calcium concentration of the medium affect the GSH/GSSG ratio of dispersed parathyroid cells. Changes in the GSH/GSSG ratio induced by calcium may be related to changes in PTH secretion.

Animals↗
PubMed1992

Effects of sulfide and low redox potential on the inhibition of nitrous oxide reduction by acetylene in Pseudomonas nautica.

Membrane introduction mass spectrometry was used to investigate the inhibitory effect of acetylene on the nitrous oxide reductase activity of intact cells of Pseudomonas nautica. We studied the effects of the concentrations of nitrate and sulfide, and the redox potential, which have all been implicated in causing a decrease in the inhibitory effects of acetylene during measurements of denitrification in natural environments. There was no evidence that the concentration of nitrate influenced the effect of acetylene. Lowering the redox potential with the reductant Ti(III)-nitrilotriacetate caused a slight alleviation of acetylene inhibition. Much greater effects at the same redox potential were obtained with concentrations of sulfide in the range 1-10 microM.

Acetylene↗
PubMedDate not supplied

[Oscillations in the oxidation-reduction potential of the brain tissue in rats developing during wakefulness and slow-wave sleep].

Variations of the brain cortex redox state potential (E) were recorded in freely moving white rats (mass of 300-350 g) with implanted platinum electrodes (with the platinum reference electrode in the nasal bone) during sleep-wake cycles. It was found that transitions from the slow-wave sleep to wakefulness were accompanied in the number of cortical areas (metabolic-active sites) by the E rise, while the transitions from the wakefulness to slow-ware sleep were associated with a drop of E. However, the episodes of the short-term arousals during the slow-wave sleep were accompanied by the respective decreases in E thus forming the irregular E variations (1.5-3 min in duration). It was also found that the oscillations of a typical pattern (quasisinusoidal with the frequency of 10-20 osc/min and the amplitudes up to several mV) could take place in the metabolic-active cortical sites. These oscillations were defined as fast E oscillations. During the slow-wave sleep, the less regular oscillations with the lower frequency (1.2-10 osc/min) and higher amplitude were recorded in the same cortical sites. These oscillations were defined as slow. It is suggested that the fast metabolic oscillations of wakefulness are mainly controlled by the mitochondria of neuronal populations, whereas the slow metabolic oscillations which occur in the slow-wave sleep are related with glycolysis in populations of glial cells.

Animals↗
PubMed1987

Cyclical oxidation-reduction of the C3 position on bile acids catalyzed by 3 alpha-hydroxysteroid dehydrogenase. II. Studies in the prograde and retrograde single-pass, perfused rat liver and inhibition by indomethacin.

[3 beta-3H, 24-14C]Lithocholic, chenodeoxycholic, and cholic acids were administered in tracer bolus doses either prograde or retrograde in the isolated perfused rat liver. Little 3H loss from cholic acid was observed, whereas with the other bile acids, 20-40% of the administered 3H was lost in a single pass from perfusate to bile. Most of the 3H loss occurred rapidly (5 min) and was recovered as [3H]water in perfusate. Excretion of bile acids was delayed with retrograde administration, and 3H loss was more extensive. In both prograde and retrograde studies, indomethacin markedly inhibited the excretion of the bolus of bile acid into bile. Indomethacin inhibited the extraction of glycocholate (50 microM) during steady state perfusion without affecting transport maximum for excretion. At lower glycocholate concentration (5 microM), indomethacin inhibited both extraction and excretion. A greater effect was seen on excretion in the latter case, which suggests that displacement of bile acid from the cytosolic protein lead to redistribution in the hepatocyte as well as reflux into the sinusoid. These data suggest that binding of bile acids to cytosolic 3 alpha-hydroxysteroid dehydrogenases occurs extensively during hepatic transit and is important in mediating the translocation of bile acids from the sinusoidal to canalicular pole of the cell.

3-Hydroxysteroid Dehydrogenases↗
PubMed1987

Cyclical oxidation-reduction of the C3 position on bile acids catalyzed by rat hepatic 3 alpha-hydroxysteroid dehydrogenase. I. Studies with the purified enzyme, isolated rat hepatocytes, and inhibition by indomethacin.

We recently identified that the Y' bile acid binders are 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSD). In the present studies, purified 3 alpha-HSD catalyzed rapid 3H loss from [3 beta-3H, C24-14C]lithocholic and chenodeoxycholic acids without net conversion to 3-oxo bile acids under physiologic pH and redox conditions. [3 beta-3H]Cholic acid was a poor substrate. The Y' fraction of hepatic cytosol was exclusively responsible for this activity and 3H was transferred selectively to NADP+. Time-dependent 3H loss was also seen in isolated hepatocytes. Further hydroxylation products of lithocholic and chenodeoxycholic acids lost 3H at the same rate, whereas 3H loss from lithocholic acid rapidly ceased, which suggests compartmentation of this bile acid in hepatocytes. Indomethacin inhibited 3H loss from bile acids either in incubations with the pure enzyme or in isolated hepatocytes. Indomethacin did not alter the initial uptake rate of bile acids by hepatocytes, but caused a redistribution of unconjugated bile acids into the medium at early time points (2.5 and 5.0 min) and that of conjugated bile acids at later time intervals (30 min). 3H loss from the 3 beta position therefore can be used to probe the interaction between bile acids and cytosolic 3 alpha-HSD in intact cells, and indomethacin is capable of inhibiting this interaction.

3-Hydroxysteroid Dehydrogenases↗