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PubMed1998

Oral L-glutamine therapy for sickle cell anemia: I. Subjective clinical improvement and favorable change in red cell NAD redox potential.

Previously, we demonstrated that there is an increased utilization of glutamine by intact sickle red blood cells (RBC) in conjunction with nicotinamide adenine dinucleotide (NAD) metabolism in vitro. In this report, we describe the in vivo effect of L-glutamine supplementation on total NAD, nicotinamide adenine dinucleotide reduced (NADH), and NAD redox potential of sickle RBC. Seven adult sickle cell anemia patients participated in this study. The exclusion criteria were pregnancy, previous or current use of hydroxyurea, and transfusion within 3 months of initiation of the study. After proper consent, L-glutamine was started at a dose of 30 g/day administered orally. Fasting blood samples were drawn at baseline and after 4 weeks of therapy by routine phlebotomy for evaluation of RBC total NAD and NADH levels. We found significant changes in both the NADH level and NAD redox potential (ratio of NADH to NAD+ + NADH). NAD redox potential increased from 47.2 +/- 3.7% to 62.1 +/- 11.8% (P < 0.01). The NADH level increased from 47.5 +/- 6.3 to 72.1 +/- 15.1 nmol/ml RBC (P < 0.01). The total NAD level demonstrated an upward trend (from 101.2 +/- 16 to 116.4 +/- 14.7 nmol/ml RBC) but this was not statistically significant. Our data show that oral L-glutamine can significantly increase the NAD redox potential and NADH level in sickle RBC. These changes may decrease oxidative susceptibility of sickle RBC and result in clinical benefit.

Administration, Oral↗
PubMed1978

Redox potentials in hydro-organic media at normal and subzero temperatures. Ferro-ferricyanide and cytochrome c as models.

Redox potentials of ferro-ferricyanide and cytochrome c were measured in water/ethylene glycol and water/dimethylsulfoxide (volume ratio from 100/0 to 50/50) between 25 and -25 degrees C. For both systems, the midpoint potential decreases in the presence of organic solvents and increases by cooling. The magnitude of these variations is larger in dimethylsulfoxide than in ethylene glycol; moreover in the same solvent mixture it is larger with ferro-ferricyanide than with cytochrome c, so that the difference between the redox potentials of these two systems can be strongly affected and even reversed. While in pure water (cacodylate buffer pH 7.0, NaCl 0.1 M) they are respectively +388 and +265 mV, in 50% dimethylsulfoxide at 25 degrees C they decrease to +112 and +208 mV. Reduction of cytochrome c by ferro-ferricyanide, in this mixture, is then expected and was indeed observed. On the other hand, as (deltaE/deltaT)T, (E being the redox potential) is higher for ferro-ferricyanide than for cytochrome c, the oxidative power of the former for the latter is expected to increase as temperature decreases. This effect was observed in 50% ethylene glycol at -16 degrees C. Organic solvents and large temperature variations appear then as powerful perturbants of redox reactions. Their effects should be taken into account in studies of redox reactions carried out in cooled hydro-organic media.

Cytochrome c Group↗
PubMed2000

Lucigenin: redox potential in aqueous media and redox cycling with O-(2) production.

The use of lucigenin luminescence as a measure of ¿O-(2) has been questioned because lucigenin has been shown to be capable of mediating the production of O-(2). This being the case, lucigenin can signal the presence of O-(2) even in systems not producing it in the absence of lucigenin. The reduction potential of lucigenin should be in accord with its ability to mediate O-(2) production; but it has not heretofore been measured in aqueous media. The problems facing such measurement are the insolubility of the divalently reduced form, which deposits on the electrode, and the slow conformational transition that follows the second electron transfer and which interferes with reversibility. We have now used rapid scan cyclic voltammetry to determine that the reduction potential for lucigenin is -0.14 +/- 0.02 V versus the normal hydrogen electrode. This value applies to both the first and the second electron transfers to lucigenin and it is in accord with the facile mediation of O-(2) production by this compound.

Acridines↗
PubMed2005

Redox potentials of chlorophylls in the photosystem II reaction center.

Water oxidation generating atmospheric oxygen occurs in photosystem II (PSII), a large protein-pigment complex located in the thylakoid membrane. The recent crystal structures at 3.2 and 3.5 A resolutions provide novel details on amino acid side chains, especially in the D1/D2 subunits. We calculated the redox potentials for one-electron oxidation of the chlorophyll a (Chla) molecules in PSII, considering the protein environment in atomic detail. The calculated redox potentials for the dimer Chla (P(D1/D2)) and accessory Chla (Chl(D1/D2)) were 1.11-1.30 V relative to the normal hydrogen electrode at pH 7, which is high enough for water oxidation. The D1/D2 proteins and their cofactors contribute approximately 390 mV to the enormous upshift of 470 mV compared to the redox potential of monomeric Chla in dimethylformamide. The other subunits are responsible for the remaining 80 mV. The high redox potentials of the two accessory Chla Chl(D1/D2) suggests that they also participate in the charge separation process.

Chlorophyll↗
PubMed1997

Effects of redox potential and hydroxide inhibition on the pH activity profile of fungal laccases.

The electronic absorption spectrum, susceptibility to fluoride inhibition, redox potential, and substrate turnover of several fungal laccases have been explored as a function of pH. The laccases showed a single spectrally detectable acid-base transition at pH 6-9 and a fluoride inhibition that diminished by increased pH (indicating a competition with hydroxide inhibition). Relatively small changes in the redox potentials (< or = 0.1 V) of laccase were observed over the pH 2.7-11. Under the catalysis of laccase, the apparent oxidation rates (kcat and kcat/Km) of two nonphenolic substrates, potassium ferrocyanide and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid), decreased monotonically as the pH increased. In contrast, the apparent oxidation rates (kcat and kcat/Km) of three 2,6-dimethoxyphenols (whose pKa values range from 7.0 to 8.7) exhibited bell-shaped pH profiles whose maxima were distinct for each laccase but independent of the substrate. By correlating these pH dependences, it is proposed that the balance of two opposing effects, one generated by the redox potential difference between a reducing substrate and the type 1 copper of laccase (which correlates to the electron transfer rate and is favored for a phenolic substrate by higher pH) and another generated by the binding of a hydroxide anion to the type 2/type 3 coppers of laccase (which inhibits the activity at higher pH), contributes to the pH activity profile of the fungal laccases.

Fungi↗
PubMed1991

The effects of surface charges on the redox potential of cytochrome c2 from the purple phototrophic bacterium Rhodobacter capsulatus.

Four site-directed mutants of Rhodobacter capsulatus cytochrome c2, which substitute lysines at three positions with aspartate or glutamate, have been prepared. Mutations included the single charge substitutions K12D, K14E, and K32E and a double charge substitution K14E/K32E. Characterization of the ionic strength dependence of the wild-type and mutant redox potentials in the "nonbinding" buffer Tris-cacodylate suggests that (i) at zero ionic strength introduction of negatively charged groups stabilizes the oxidized state by 11-14 mV per charge and (ii) at high ionic strengths where the charged groups are masked, the effects of single charge substitutions are overcome; however, the redox potential of the double charge substitution is still affected. These results indicate that at physiological ionic strengths charge distribution only affects redox potential when the heme environment has been perturbed by a structural perturbation and that the determinants of redox potential in c-type cytochromes is primarily due to the local heme environment.

Aspartic Acid↗
PubMed1996

A study of a series of recombinant fungal laccases and bilirubin oxidase that exhibit significant differences in redox potential, substrate specificity, and stability.

A series of fungal laccases (Polyporus pinsitus, Rhizoctonia solani, Myceliophthora thermophila, Scytalidium thermophilum) and one bilirubin oxidase (Myrothecium verrucaria) have been studied to determine their redox potential, specificity, and stability. Polyporus and Rhizoctonia laccases possess potentials near 0.7-0.8 V (vs. NHE), while other oxidases have potentials near 0.5 V. It is observed that higher redox potential correlates with higher activity. By EPR, no significant change in the geometry of type 1 copper (II) site is observed over this series. At the optimal pH, the two substrates studied, 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) and syringaldazine, show Km values ranging form 10 to 120 and from 1 to 45 microM; and kcat values ranging from 50 to 16 000 and 200 to 3000 per min, respectively. The enzymes are more stable in the neutral-alkaline pH range. The thermal stability is in the order of bilirubin oxidase equivalent to Myceliophthora laccase equivalent to Scytalidium laccase > Polyporus laccase > Rhizoctonia laccase. Based on these results and the sequence alignments made against Zucchini ascorbate oxidase it is speculated that structural differences in the substrate-activation site (a 'blue', type 1 copper center) control the redox potential range as well as substrate specificity, and the cystine content contributes to stability.

Electron Spin Resonance Spectroscopy↗
PubMed2000

Desferrioxamine (DFO) conjugated with starch decreases NAD redox potential of intact red blood cells (RBC): evidence for DFO as an extracellular inducer of oxidant stress in RBC.

Desferrioxamine (DFO) is an important iron-chelating agent. It has also been thought of as an agent with anti-oxidant potential as it chelates ferric iron in various parts of the body. However, there is evidence suggesting that it may paradoxically affect red blood cells (RBCs) by inducing intracellular oxidant stress. Recently we observed that incubation of RBCs with DFO decreases NAD redox potential in normal RBC. To further understand the mechanism of DFO's interaction with RBC, we conducted a study to determine the effect of extracellular DFO upon RBC's redox status. We examined NAD redox potential in intact RBC (N = 7) incubated with DFO conjugated to starch. RBCs were incubated with 4 mM DFO for 3(1/2) hr and with 6 mM DFO for 2 and 3(1/2) hr. Significant decreases in NAD redox potential were observed after the incubations. With 4 mM DFO at the 3 (1/2) hr time point the mean decrease was 12.37% +/- 9.96% (P < 0.0085). With 6 mM DFO, the mean decreases were 18.54% +/- 9.79% (P < 0.0013) and 19.16% +/- 8.78% (P < 0.0006) for the 2 and 3 (1/2) hr incubations, respectively. DFO by itself is very poorly permeable to RBC. Conjugation with starch further ensured impermeability of DFO. The data presented here confirm the oxidant effect of DFO on RBC. The data also demonstrate that the effect of DFO on RBC's NAD redox potential originates extracellularly.

Adult↗
PubMed1999

The effect of redox potential changes on reductive dechlorination of pentachlorophenol and the degradation of acetate by a mixed, methanogenic culture

The effect of changes in redox potential on methanogenesis from acetate, and on the reductive dechlorination of pentachlorophenol (PCP), was evaluated using a computer-monitored and feedback-controlled bioreactor. PCP was transformed via 2,3,4, 5-tetrachlorophenol (2,3,4,5-TeCP) to 3,4,5-trichlorophenol (3,4, 5-TCP). In 6- to 12-d experiments, pH, acetate concentration, and temperature were held constant; the redox potential, defined here as the potential measured at a platinum electrode (EPt), was maintained at different set points, while transformation of multiple PCP additions was monitored. Without redox potential control, the value of EPt for the culture was approximately -0.26 V (vs. SHE). The value of EPt was elevated from -0.26 V for periods up to 10 h by computer-controlled addition of H2O2 or K3Fe(CN)6. Methanogenesis continued during a relatively mild shift of EPt to -0.2 V with H2O2, but was halted when EPt was raised to -0.1 V with either H2O2 or K3Fe(CN)6. Methanogenesis resumed when EPt returned to -0.26 V. During periods in which EPt was elevated significantly and methanogenesis stopped, transformation of PCP and 2,3,4,5-TeCP continued at progressively slower rates, but the rate of 2,3,4, 5-TeCP transformation was diminished to a greater extent. When a small volume of pure H2 was added to the reactor headspace, while EPt was maintained at -0.1 V, reductive dechlorination rates increased dramatically. Lower H2 concentrations during periods of oxidant addition, perhaps due to the effect of the oxidant on H2-producing bacteria, may contribute to decreased reductive dechlorination rates. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗
PubMed2005

Calculation of the redox potential of the protein azurin and some mutants.

Azurin from Pseudomonas aeruginosa is a small 128-residue, copper-containing protein. Its redox potential can be modified by mutating the protein. Free-energy calculations based on classical molecular-dynamics simulations of the protein and from mutants in aqueous solution at different pH values were used to compute relative redox potentials. The precision of the free-energy calculations with the lambda coupling-parameter approach is evaluated as function of the number and sequence of lambda values, the sampling time and initial conditions. It is found that the precision is critically dependent on the relaxation of hydrogen-bonding networks when changing the atomic-charge distribution due to a change of redox state or pH value. The errors in the free energies range from 1 to 10 k(B)T, depending on the type of process. Only qualitative estimates of the change in redox potential by protein mutation can be obtained.

Amino Acid Substitution↗
PubMed1982

Characterization of electron donation to cytochrome c-555 in Chromatium vinosum from ferrocyanide, tetramethylphenylenediamine and reduced dimethylquinone. Effects of redox potential, pH and salt concentration.

1. The dependences of the reduction of ferricytochrome c-555 in the reaction center-cytochrome c complex on the redox potential and pH were investigated using N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), ferrocyanide, and reduced 2,5-dimethyl-p-quinone as electron donors. 2. In the reduction of cytochrome c-555 by TMPD, the unprotonated form was the exclusive electron donor to the cytochrome with a second-order rate constant of 1.0 X 10(5) M-1.s-1. 3. Ferrocyanide reduced cytochrome c-555 slowly with a rate constant of 7.8 X 10(3) M-1.s-1 at infinite salt concentration. The value of -5.2 X 10(-4) elementary charge/A2 was estimated as the surface charge density in the vicinity of cytochrome c-555 by analyzing the salt effect on the cytochrome reduction using the Gouy-Chapman theory. 4. The characteristics of the dependences of the reduction of cytochrome c-555 by reduced 2,5-dimethyl-p-quinone on the redox potential and pH were well explained by the redox potential and pH dependences of the formation of the semiquinone. In the neutral-to-alkaline pH range the anionic semiquinone was the main electron-donating species with a second-order rate constant of 6.0 X 10(7) m-1.s-1.

Bacterial Chromatophores↗
PubMed1988

[Changes in the redox potential and the number of accessible sulfhydryl groups in Escherichia coli and Bacillus subtilis cultures during transient processes].

It was shown that changes in the redox potential can be due to the influence of compounds which alter the intracellular pH (acetate or propionate, protonophore carbonyl-cyanide-m-chlorophenyl hydrazone, permeate cation TPP+). A correlation was found between the redox potential changes and the number of SH-groups in the medium and on cell surface. It was shown also that the previously reported redox potential shifts during the transition of E. coli and B. subtilis cultures to the stationary phase under glucose or ammonium exhaustion are due to the increase in the number of SH-groups in the medium and on cell surface. A hypothesis is put forward, according to which the changes in intracellular pH play a trigger role, whereas those in the thiol: disulfide ratio inside and outside the cells are thought to amplify regulatory signals.

Acetates↗
PubMed2004

Green chemistry methods in sulfur dyeing: application of various reducing D-sugars and analysis of the importance of optimum redox potential.

The importance of sulfur dyeing of cellulosic fibers, particularly cotton, is realized economically throughout the dyeing industry. At the present time, dyeing with sulfur dyes requires the use of various auxiliaries, many of which have adverse effects on the environment. The most damaging of these is the reducing agent sodium sulfide, required to reduce the dye molecules to a water-soluble leuco form to enable adsorption and diffusion into the fiber. In this study, attempts have been made to replace the sodium sulfide used within the sulfur dyeing process with a variety of environmentally friendly reducing sugars. The redox potential of various hexose and pentose monosaccharides and reducing disaccharides was recorded and compared. Subsequently, cotton was dyed with the world's most important sulfur dye, C. I. Sulfur Black 1, using the reducing sugars under alkaline conditions, and compared to dyeings secured by employing commercial sulfide reducing agents. It was observed that reducing sugars gave comparable, and in many cases superior, color strength and wash fastness results, with respect to the commercial sulfide-based reducing agents, which still account for the vast majority of sulfur dyeing processes and that pose significant environmental concern. Employment of reducing sugars in sulfur dyeing could provide a sustainable, nontoxic, biodegradable, cost-effective alternative to sodium polysulfide and sodium hydrogen sulfide. Comparison of the redox potential of reducing sugars against the color strength of the dyeings secured demonstrated that there was an optimum redox potential of around -650 mV for maximum color strength achieved. The same redox potential also conferred the lowest color loss upon washing. These observations were attributed to reduction of the polymeric dye molecules to an optimum size for fiber affinity and diffusion into the fiber, but which would also confer maximum wash fastness upon oxidation.

Carbohydrates↗
PubMed1972

Redox potential measurements for determining the disinfecting power of chlorinated water.

The kill of Escherichia coli within 3 min. was studied in chlorine-demand-free water using sodium hypochlorite, monochloramine, dichloramine, halazone, chloramine T, cyanuric acid + sodium hypochlorite and cyanuric acid + monochloramine. The redox potential and the available chlorine were measured. The redox potential was found to be better correlated with the disinfecting property of the water than was the amount of available chlorine. For individual pure chlorine compounds, the measuring of available chlorine showed in general a somewhat better correlation with reduction of the bacteria than the redox potential showed.

Benzoates↗
PubMed2006

Electrochemical modification of the redox potential of pasteurized milk and its evolution during storage.

Several modifications that occur in milk during its processing and storage are driven by different oxidation-reduction reactions. In this study, a smooth electrolytic process was used to modify the redox state of the active species of milk thereby creating a mean to control these reactions. Five electroreduction treatments (2, 4, 6, 8, and 10 V) were applied to pasteurized skim milk. Parameters such as redox potential, dissolved oxygen, pH, conductivity, and current intensity were monitored during the course of each treatment. The proposed technology allows modulation of the redox potential of milk. Significant decreases of redox potential (441-707 mV) and of dissolved oxygen (3.3-8.3 mg L(-1)) were obtained. However, the results suggest that only a short-term modulation is created and that natural "milk equilibrium" is reestablished after 4-5 days of storage depending on the voltage difference applied during the electrochemical treatment.

Animals↗
PubMed1994

Calculation of the redox potentials of iron-sulfur proteins: the 2-/3-couple of [Fe4S*4Cys4] clusters in Peptococcus aerogenes ferredoxin, Azotobacter vinelandii ferredoxin I, and Chromatium vinosum high-potential iron protein.

Calculations of the redox potentials of the 2-/3-couples of [Fe4S*4Cys4] clusters in the iron-sulfur proteins Peptococcus aerogenes ferredoxin (PaFd), Azotobacter vinelandii ferredoxin I (AvFdI) and Chromatium vinosum high potential iron protein (CvHiPIP) based on the Protein Dipoles Langevin Dipoles (PDLD) method are reported. The structures of these proteins have been determined by X-ray crystallography; in the case of PaFd the structure has recently been revised due to a change in the sequence close to Cluster II. The large differences between the potentials of the [Fe4S*4Cys4] clusters of PaFd and AvFdI and the potential of the [Fe4S*4Cys4] cluster of CvHiPIP are successfully modeled and originate principally in differences in the configuration of main-chain amide groups near the clusters. The small difference between the potentials of PaFd and AvFdI is also satisfactorily modeled in the case of Cluster I of PaFd. Solvent dipoles close to the cluster in PaFd are an important contributor to its higher potential. The two X-ray structures of PaFd yield similar results for Cluster I of PaFd. In contrast, the results for Cluster II differ substantially; for reasons not yet clear, the recently revised structure leads to results in worse agreement with experiment.

Amino Acid Sequence↗
PubMed2005

Considerations on the mechanism of photosynthetic water oxidation - dual role of oxo-bridges between Mn ions in (i) redox-potential maintenance and (ii) proton abstraction from substrate water.

Two mechanistic problems of photosynthetic water oxidation at the Mn complex of Photosystem II (PS II) are considered. (I) In the four Mn-oxidizing transitions, any pure Mn oxidation is predicted to cause an increase in redox potential that renders subsequent oxidation steps impossible (redox-potential problem). Formation of unprotonated oxo-bridges may counteract the potential increase. (II) The O-O formation step without any high-pK bases acting as proton acceptors is energetically unfavorable (acceptor-base problem). The pK of oxides in a bridging position between Mn ions may increase drastically upon reduction of Mn in the water-oxidation step (>10 units), thus rendering them favorable proton acceptors. It is proposed that in PS II, in the course of the four oxidizing transitions at least two unprotonated oxo-bridges are formed. Thereby (i) a redox potential increase is prevented and (ii) proton acceptors are prepared for the O-O formation step. Water oxidation in the O-O bond formation step is facilitated by simultaneous Mn reduction and proton transfer to bridging oxides amounting to hydrogen atom or hydride transfer from substrate water to the Mn-oxo core of the Mn complex of PS II.

Manganese↗
PubMed2002

The influence of redox potential on the degradation of halogenated methanes.

To determine the influence of redox potential on the reaction mechanism and to quantify kinetics of the dechlorination by digester sludge, the test compounds trichlorofluoromethane (CFCl3), carbon tetrachloride (CCl4), and chloroform (CHCl3) were incubated in the presence of sludge and variable concentrations of reducing agent. Different sources of dehalogenation were examined, including live sludge and heat-killed sludge, and abiotic mechanisms were quantified in the absence of sludge. Batch incubations were done under redox conditions ranging from +/-534 to -348 mV. The highest rates for the dehalogenation of the three compounds were observed at -348 mV. The dechlorination rate of all the compounds by the heat-resistant catalysts was approximately twofold higher than the live treatments. It was proposed that the higher degradation rates by heat-killed sludge were due to the absence of physical barriers such as cell wall and cell membranes. There was no abiotic dechlorination of CFCl3, whereas CCl4 and CHCl3 were both reduced in the absence of sludge catalyst by Ti (III) citrate at > or =2.5 mM. The degradation pathways of CFCl3 and CHCl3 appeared to be only partially reductive since the production of reduced metabolites was low in comparison with the total amount of original halogenated compounds degraded. For CFCl3, the partial reductive degradation implied that different intra- and extracellular pathways were concurrent. The Gibbs free energy and the redox potential for the dehalogenation reactions utilizing Ti (III) citrate and acetate as electron donors are reported here for the first time.

Carbon Tetrachloride↗