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PubMedDate not supplied

[Dynamics of the redox potential in a fed-batch culture of E. coli].

Dynamics of Eh, pH, pO2 and optical density in E. coli cultures under glucose and ammonium exhaustion were studied. It has been shown that changes in the redox potential accompanying the exhaustion of these substances in aerobic cultures are the leaps by their character and reflect the physiological state of cells and changes in the structure of cell surface. A relationship between the changes in the redox potential and in the electrochemical potential of H ions (delta mu H) is suggested.

Culture Media↗
PubMed2005

Using redox potential to detect microbial activities during clavulanic acid biosynthesis in Streptomyces clavuligerus.

Production of clavulanic acid (CA) by Streptomyces clavuligerus in a shake-flask culture increased from 92 to 180 mg l(-1) with an increased O2 transfer efficiency (0.039 --> 0.058 s(-1)), which maintained the redox potential values above -250 mV. Compared with traditional measures, such as dissolved O2 concentration and respiratory activity, the redox potential can easily be determined and correlates closely with CA production. It can therefore be used to monitor microbial activities during biosyntheses of secondary metabolites.

Bioreactors↗
PubMedDate not supplied

Predicting dye biodegradation from redox potentials.

Two biological approaches for decolorization of azo sulfonated dyes have been compared: reductive decolorization with the ascomycete yeast Issatchenkia occidentalis and enzymatic oxidative decolorization with Trametes villosa laccase alone or in the presence of the mediator 1-hydroxybenzotriazole. The redox potential difference between the biological cofactor involved in the reductive activity of growing cells and the azo dye is a reliable indication for the decolorization ability of the biocatalyst. A linear relationship exists between the redox potential of the azo dyes and the decolorization efficiency of enzyme, enzyme/mediator, and yeast. The less positive the anodic peak of the dye, the more easily it is degraded oxidatively with laccase. The more positive the cathodic peak of the dye, the more rapidly the dye molecule is reduced with yeast.

Algorithms↗
PubMed1990

Reduced arterial ketone body ratio during laparotomy: an evaluation of operative stress through the changes in hepatic mitochondrial redox potential.

The present article discusses the evaluation of surgical stress on the basis of the hepatic functional capacity of each patient. The changes in arterial blood ketone body ratio (KBR; acetoacetate/beta-hydroxybutyrate), which reflects hepatic mitochondrial redox potential, following intraoperative procedures were investigated in 60 laparotomy cases, including 30 cases with partial hepatectomy. The time course of changes in KBR was obtained by serial measurement during operation. The total area below the KBR level of 0.7 was defined as the hepatic stress score (HSS). HSS was significantly greater in the cases with hepatectomy (43.5 +/- 9.1; mean +/- SE) than in others (16.5 +/- 4.2; p less than 0.01). HSS in 13 patients accompanied by postoperative complications (60.4 +/- 17.7) was also significantly greater than that in the patients with uneventful postoperative courses (22.1 +/- 4.3; p less than 0.05). The former was also accompanied by significantly larger postoperative catabolic response preceding the clinical onset of complications (p less than 0.001). In the cases with uneventful postoperative courses, analysis of variance revealed that nitrogen balance and catabolic index in the first postoperative week were dependent on HSS negatively and positively, respectively (p less than 0.005), indicating a causative relationship between the suppression of hepatic energy metabolism during operation and the enhanced postoperative catabolic response. These results suggest that total surgical stress in major laparotomy can be quantitated and evaluated through the magnitude of decrease in hepatic mitochondrial redox potential, and that this evaluation may provide valuable information for intraoperative and postoperative patient care.

3-Hydroxybutyric Acid↗
PubMed1998

Redox potential of the haem c group in the quinocytochrome, lupanine hydroxylase, an enzyme located in the periplasm of a Pseudomonas sp.

The quinocytochrome c, lupanine hydroxylase, was shown to be located in the periplasm of a Pseudomonas sp. The midpoint redox potential of the haem in the purified enzyme was measured by potentiometric titration and shown to be +193 mV. PQQ was removed from the enzyme by isoelectric focusing to give inactive apoenzyme. This resulted in a shift in the midpoint redox potential of the haem to +98 mV. Full activity was recovered by the addition of PQQ to apoenzyme that also restored the original potential.

Cell Fractionation↗
PubMed2004

Tuning of redox potentials for the design of ruthenium anticancer drugs -- an electrochemical study of [trans-RuCl(4)L(DMSO)](-) and [trans-RuCl(4)L(2)](-) complexes, where L = imidazole, 1,2,4-triazole, indazole.

The electrochemical behavior of [trans-RuCl(4)L(DMSO)](-) (A) and [trans-RuCl(4)L(2)](-) (B) [L = imidazole (Him), 1,2,4-triazole (Htrz), and indazole (Hind)] complexes has been studied in DMF, DMSO, and aqueous media by cyclic voltammetry and controlled potential electrolysis. They exhibit one single-electron Ru(III)/Ru(II) reduction involving, at a sufficiently long time scale, metal dechlorination on solvolysis, as well as, in organic media, one single-electron reversible Ru(III)/Ru(IV) oxidation. The redox potential values are interpreted on the basis of the Lever's parametrization method, and particular forms of this linear expression (that relates the redox potential with the ligand E(L) parameter) are proposed, for the first time, for negatively (1-) charged complexes with the Ru(III/II) redox couple center in aqueous phosphate buffer (pH 7) medium and for complexes with the Ru(III/IV) couple in organic media. The E(L) parameter was estimated for indazole showing that this ligand behaves as a weaker net electron donor than imidazole or triazole. The kinetics of the reductively induced stepwise replacement of chloride by DMF were studied by digital simulation of the cyclic voltammograms, and the obtained rate constants were shown to increase with the net electron donor character (decrease of E(L)) of the neutral ligands (DMSO < indazole < triazole < imidazole) and with the basicity of the ligated azole, factors that destabilize the Ru(II) relative to the Ru(III) form of the complexes. The synthesis and characterization of some novel complexes of the A and B series are also reported, including the X-ray structural analyses of (Ph(3)PCH(2)Ph)[trans-RuCl(4)(Htrz)(DMSO)], [(Ph(3)P)(2)N][trans-RuCl(4)(Htrz)(DMSO)], (H(2)ind)[trans-RuCl(4)(Hind)(DMSO)], and [(Hind)(2)H][trans-RuCl(4)(Hind)(2)].

Antineoplastic Agents↗
PubMed1989

[Changes in the redox potential of serum samples following in vitro irradiation--an indicator of malignant tumor growth].

In serum samples of healthy persons and patients with malignant neoplasia the reduction-oxidation-potentials were determined. Measurements were made in untreated sera and after irradiation with different doses. Sera of healthy persons showed a decrease that of tumor patients an increase of redox-potential values. With this method malignant tumor growth can be demonstrated. It does not yet permit any statements on tumor localisation. On the other hand conclusions seem to be possible on growth speed of neoplasia. To our hitherto existing experiences estimations of redox-potential are applicable to the diagnosis of fast growing recurrences and metastases in tumor after-care, but can also support the therapeutic procedure decisively in defined differential diagnostic problems and in tumors of dignity in question.

Blood↗
PubMed1998

Dislocation of type I membrane proteins from the ER to the cytosol is sensitive to changes in redox potential.

The human cytomegalovirus (HCMV) gene products US2 and US11 dislocate major histocompatibility class I heavy chains from the ER and target them for proteasomal degradation in the cytosol. The dislocation reaction is inhibited by agents that affect intracellular redox potential and/or free thiol status, such as diamide and N-ethylmaleimide. Subcellular fractionation experiments indicate that this inhibition occurs at the stage of discharge from the ER into the cytosol. The T cell receptor alpha (TCR alpha) chain is also degraded by a similar set of reactions, yet in a manner independent of virally encoded gene products. Diamide and N-ethylmaleimide likewise inhibit the dislocation of the full-length TCR alpha chain from the ER, as well as a truncated, mutant version of TCR alpha chain that lacks cysteine residues. Cytosolic destruction of glycosylated, ER-resident type I membrane proteins, therefore, requires maintenance of a proper redox potential for the initial step of removal of the substrate from the ER environment.

Cell Line↗
PubMed2002

Catalytic properties, thiol pK value, and redox potential of Trypanosoma brucei tryparedoxin.

The dithiol protein tryparedoxin is a component of the unique trypanothione/trypanothione reductase metabolism of trypanosomatids and is involved in the parasite synthesis of deoxyribonucleotides and the detoxication of hydroperoxides. Tryparedoxin is a highly abundant protein in all life stages of Trypanosoma brucei, the causative agent of African sleeping sickness. As shown here, its functional properties are intermediate between those of classical thioredoxins and glutaredoxins. The redox potential of T. brucei tryparedoxin of -249 mV was determined by protein-protein redox equilibration with Escherichia coli thioredoxin. The trypanothione/tryparedoxin couple is probably the most significant factor determining the cytosolic redox potential of the parasites. The pK value of Cys(40), the first thiol in the WCPPC motif, is 7.2 as derived from the thiolate absorption at 240 nm and the rate of carboxymethylation. Alteration of the active site into that of thioredoxin (CGPC) did not affect the pK value. In contrast, in the mutant with the glutaredoxin motif (CPYC) the pK dropped to < or =4.0. The fact that the pK value of tryparedoxin coincides with the intracellular pH of the parasite may contribute to the reactivity of tryparedoxin in thiol disulfide exchange reactions.

Alkylation↗
PubMed1978

The mechanism of reduction of the ubiquinone pool in photosynthetic bacteria at different redox potentials.

(1) A flash number dependency of flash-induced absorbance changes was observed with whole cells of Rhodospirillum rubrum and chromatophores of R. rubrum and Rhodopseudomonas sphaeroides wild type and the G1C mutant. The oscillatory behavior was dependent on the redox potential; it was observed under oxidizing conditions only. Absorbance difference spectra measured after each flash in the 275--500 nm wavelength region showed that a molecule of ubiquinone, R, is reduced to the semiquinone (R-) after odd-numbered flashes and reoxidized after even-numbered flashes. The amount of R reduced was approximately one molecule per reaction center. (2) The flash number dependency of the electrochromic shift of the carotenoid spectrum was studied with chromatophores of Rps. sphaeroides wild type and the G1C mutant. At higher values of the ambient redox potential a relatively slow phase with a rise time of 30 ms was observed after even-numbered flashes, in addition to the fast phase (completed within 0.2 ms) occurring after each flash. Evidence was obtained that the slow phase represents the formation of an additional membrane potential during a dark reaction that occurs after flashes with an even number. This reaction is inhibited by antimycin A, whereas the oscillations of the R/R- absorbance changes remain unaffected. At low potentials (E = 100 mV) no oscillations of the carotenoid shift were observed: a fast phase was followed by a slow phase (antimycin-sensitive) with a half-time of 3 ms after each flash. (3) The results are discussed in terms of a model for the cyclic electron flow as described by Prince and Dutton (Prince, R.C. and Dutton, P.L. (1976) Bacterial Photosynthesis Conference, Brussels, Belgium, September 6--9, Abstr. TB4) employing the so-called Q-cycle.

Bacterial Chromatophores↗
PubMed1997

Assignment of the ligand geometry and redox potentials of the trihaem ferricytochrome c3 from Desulfuromonas acetoxidans.

Cytochrome c551.5 is a trihaem cytochrome of the cytochrome c3 family isolated from Desulfuromonas acetoxidans. Although several X-ray structures are available for tetrahaem cytochromes of this family, there is no X-ray structure for trihaem cytochromes. Cytochrome C551.5 was studied in the oxidized form by means of two-dimensional NMR. The pattern of observed interhaem NOESY connectivities is in agreement with the haem core structure previously determined by NMR for the reduced protein [Coutinho, I. B., Turner, D. L., Liu, M. Y., LeGall, J. & Xavier, A. V. (1996) J. Biol. Inorg. Chem. 1, 305-311]. The similarities found between the haem core structure and the amino acid sequence of cytochrome c551.5 and those of tetrahaem cytochromes c3 allows each of the haems to be specifically assigned in the polypeptide sequence, and the attribution of the midpoint redox potentials to the individual haems. This also allows individual redox potentials to be assigned to each haem in the NMR spectrum. The paramagnetic shifts of the 13C resonances of the haem substituents were analyzed in terms of pi molecular orbitals with perturbed D4h symmetry. The parameters of this analysis have been shown to be controlled by the orientation of the axial ligands in several other bis-His-coordinated haems and hence the ligand geometry was deduced for cytochrome C551.5. The structural analogy between the relative haem plane orientations in cytochrome c551.5 and the tetrahaem cytochromes c3 is found to extend to the axial ligands with the largest differences being in the vicinity of the deleted fourth haem, using the numbering of cytochrome c3 haems.

Bacteria↗
PubMed1989

Effect of redox potential on the activation of the NAD-dependent hydrogenase from Alcaligenes eutrophus Z1.

A formal kinetic treatment of the autocatalytic activation cycle of the NAD-dependent hydrogenase from Alcaligenes eutrophus Z1 is presented. The value for the enzyme first-order activation rate constant is estimated to be (2.0 +/- 0.6) s-1 (pH 7.8, 25 degrees C). The effect of the redox potential on the activation properties of the NAD-dependent hydrogenase is studied. Hydrogenase activation is controlled by a midpoint redox potential of approximately -100 mV (pH 7.8). Once activated the enzyme is not immediately transformed back into an inactive state on rapid reoxidation and is able to preserve its catalytic properties for at least 3-4 h of intense oxigenation. Several lines of evidence show that the reductive activation of the NAD-dependent hydrogenase is accompanied by a structural reorganization of the protein. A possible origin of the -100 mV transition is discussed. A model for the activation process of the NAD-dependent hydrogenase is suggested.

Alcaligenes↗
PubMed1991

Hepatomuscular failure in septic catabolism: altered muscular response to plasma proteolytic factor in decreased hepatic mitochondrial redox potential.

To estimate the contribution of muscle protein in whole-body protein catabolism, the muscular contribution index (MCI; urine 3-methylhistidine/urine total nitrogen) was determined in 49 cases of elective laparotomy, together with the arterial blood ketone body ratio (KBR; acetoacetate/beta-hydroxybutyrate), which reflects hepatic mitochondrial redox potential. MCI increased after operation and the occurrence of severe infection, provided KBR was maintained above 0.7. In patients with sepsis, however, MCI decreased dependently with KBR (n = 33; p less than 0.01). In these patients, plasma proteolysis-inducing activity determined by in vitro bioassay increased in inverse proportion to KBR (n = 20, p less than 0.01). Moreover, plasma concentrations of not only aromatic but also branched-chain amino acids markedly increased when KBR decreased to below 0.4 (n = 23; p less than 0.05). Thus the role of muscle protein in septic catabolism is diminished under reduced hepatic mitochondrial redox potential, despite the rapid increase of proteolysis-inducing activity. This finally leads to the failure of amino acid uptake by muscles, as well as liver. These results suggest that the deteriorated substrate exchange may form the metabolic background for multiple systems organ failure, which is often preceded by reduced KBR.

Biomarkers↗
PubMed1997

Importance of a conserved phenylalanine-35 of cytochrome b5 to the protein's stability and redox potential.

Phenylalanine-35, which is a residue of the hydrophobic patch on the surface of cytochrome b5, has been mutated into Tyr35, His35 and Leu35 to elucidate the functions of the Phe35 and give further insight into the roles of the hydrophobic patch and/or aromatic network. The effects of these mutations on the heme environment, denaturation towards heating and the denaturant urea, redox potential and stability of protein were studied. The relative stability of cytochrome b5 and its mutants towards heating has the order Phe35Tyr > wild type > Phe35Leu > Phe35His in the oxidized state and wild type > Phe35Tyr > Phe35Leu > Phe35His in the reduced state. All the mutants exhibit decreased reduction potentials: Phe35Tyr -66 mV, Phe35His -51 mV and Phe35Leu -28 mV, which are more negative than that of the wild type. The order of redox potential reflects the relative stability in the oxidized and reduced states. A method of producing multiple mutants at a single site of a gene is also described for the first time.

Amino Acid Sequence↗
PubMed1976

The primary photoreactions in the complex cytochrome-P-890-P-760 (bacteriopheophytin760) of Chromatium minutissimum at low redox potentials.

Experimental evidence for electron transfer, photosensitized by bacteriochlorophyll, from cytochrome c to a pigment complex P-760 (involving bacteriopheophytin-760 and also bacteriochlorophyll-800) in the reaction centers of Chromatium minutissimum has been described. This photoreaction occurs between 77 and 293 degrees K at a redox potential of the medium between -250 and -530 mV. Photoreduction of P-760 is accompanied by development of a wide absorption band at 650 nm and of an EPR signal with g=2.0025+/-0.0005 and linewidth of 12.5+/-0.5 G, which are characteristic of the pigment radical anion. It is suggested that the photoreduction of P-760 occurs under the interaction of reduced cytochrome c with the reaction center state P+-890-P--760 which is induced by light. The existence of short-lived state P+-890-P--760 is indicated by the recombination luminescence with activation energy of 0.12 eV and t 1/2 less than or equal to 6 ns. This luminescence is exicted and emitted by bacteriochlorophyll and disappears when P-760 is reduced. At low redox potentials, the flash-induced absorbance changes related to the formation of the carotenoid triplet state with t 1/2 = 6 mus at 20 degreesC are observed. This state is not formed when P-760 is reduced at 293 and 160 degrees K. It is assumed that this state is formed from the reaction center state P+-890---760, which appears to be a primary product of light reaction in the bacterial reaction centers and which is probably identical with the state PF described in recent works.

Chromatium↗
PubMed1985

Effect of redox potential on protein degradation in perfused rat heart.

The effect of redox potential on protein degradation was assessed in rat hearts supplied either glucose or pyruvate, and the correlation between redox state and proteolysis was examined after the addition of insulin and leucine. In hearts supplied glucose as the sole energy source, the inhibition of protein degradation by a range of concentrations of insulin was associated with increased ratios of perfusate lactate to pyruvate and intracellular lactate to pyruvate, malate to pyruvate, and NADH to NAD. However, the extent of inhibition did not correlate with the redox state. The inhibitory effect of leucine on protein degradation was not accompanied by any change in redox state of the hearts. In hearts provided with pyruvate, rates of protein degradation continued to be inhibited by insulin even though the perfusate lactate to pyruvate was decreased by 14-fold and the calculated cytosolic NADH-to-NAD ratios were only 3% of those seen in hearts supplied glucose. These results indicated that a correlation between redox state and protein degradation was not apparent in myocardium under the experimental conditions examined.

Animals↗
PubMed1999

Changes in oxidative stress and cellular redox potential during myocardial storage for transplantation: experimental studies.

BACKGROUND: Cardioplegic solutions assure only a sub-optimal myocardial protection during prolonged storage for transplantation. The ultimate cause of myocardial damage during storage is unknown, but oxygen free radicals might be involved. We evaluated the occurrence of oxidative stress and changes in cellular redox potential after different periods of hypothermic storage. METHODS: Langendorff-perfused rabbit hearts were subjected to a protocol mimicking each stage of a cardiac transplantation procedure: explantation, storage and reperfusion. Three periods of storage were considered: Group A = 5 hours, Group B = 15 hours, and Group C = 24 hours. Oxidative stress was determined in terms of myocardial content and release of reduced (GSH) and oxidized (GSSG) glutathione, and cellular redox potential as oxidized and reduced pyridine nucleotides ratio (NAD/NADH). Data on mechanical function, cellular integrity and myocardial energetic status were collected. RESULTS: At the end of reperfusion, despite the different timings of storage, recovery of left ventricular developed pressure (46.1+/-7.0, 54.7+/-6.7, and 45.7+/-7.4% of the baseline pre-ischaemic value), energy charge (0.81+/-0.02, 0.81+/-0.02, and 0.77+/-0.01) and NAD/NADH ratio (8.87+/-1.08, 9.39+/-1.72, and 10.26+/-1.98) were similar in all groups (A, B and C). On the contrary, the rise in left ventricular resting pressure (LVRP) and GSH/GSSG ratio were significantly different between Group C, and Groups A and B (p<0.0001, analyzed by Generalized Estimating Equations model for repeated measures, and p<0.05, respectively). CONCLUSIONS: The pathophysiology of myocardial damage during hypothermic storage cannot be considered as a normothermic ischaemic injury and parameters other than energetic metabolism, such as thiolic redox state, are more predictive of functional recovery upon reperfusion.

Animals↗
PubMedDate not supplied

[Effect of the redox potential on the growth of aerobic microorganisms].

The effect of redox potential was studied on the growth of the following aerobic microorganisms: Candida utilis, Bacillus megaterium, Pseudomonas fluorescens. The action of oxidizing agents (K3Fe(CN)6, KIO3, K2Cr207 and KMnO4) and reducing agents (ascorbic acid, sodium thioglycolate, K4Fe (CN)6 and Na2S2O3) on the growth rate was investigated. K3Fe(CN)6, ascorbic acid, sodium thioglycolate and K4Fe(CN)6 were found to be suitable for buffering the Eh of the medium. The potential could be shifted by 50--200 mV by adding various reducing and oxidizing agents. The rate of growth of C. utilis, Bac. megaterium and Ps. fluorescens did not depend on the potential value.

Aerobiosis↗