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PubMedDate not supplied

On-line assessment of metabolic activities based on culture redox potential and dissolved oxygen profiles during aerobic fermentation.

We report here on the utility of on-line culture redox potential and dissolved oxygen measurements to identify metabolic changes in fermentation by Corynebacterium glutamicum under aerobic conditions. Metabolic changes were identified by observing discrepancies in the profile of culture redox potential and dissolved oxygen. On the basis of these measurements, we can identify the end of the lag phase, threonine exhaustion, and glucose exhaustion during fermentation.

Aerobiosis↗
PubMed1996

Shift of the special pair redox potential: electrostatic energy computations of mutants of the reaction center from Rhodobacter sphaeroides.

Shifts of the special pair redox potential of the photosynthetic reaction center of Rhodobacter sphaeroides are considered for several point mutations [Lin. X., Murchison, H. A., Nagarijan, V., Parson, W. W., Allen, J. P., & Williams, J. C. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269] in the neighborhood of the special pair. The shifts are calculated from electrostatic energies by solving Poisson's equation for energy-minimized structures of the reaction center. Different conditions for the evaluation of the electrostatic energy are probed. To test the influence of the hydrogen bonding at the acetyl groups of the special pair, the orientation and torsion potential of the acetyl groups are varied. The calculated shifts of the midpoint potential of double and triple mutants can approximately be obtained from the corresponding shifts of the single point mutations. The calculated shifts agree with the measured values for all single and double mutants considered. However, a clear decision between different acetyl group conformations was only possible for the mutants HF(L168) and HF(L168) + LH(L131) where the calculated shifts of the redox potential agree with experiments only if the acetyl oxygen atom at DM points toward the Mg2+ ion of DL. This is corroborated by computations of the interaction energy of the acetyl group at DM, which adopts a lower value in the wild-type reaction center if its oxygen atom is bonded to the Mg2+ ion of DL.

Bacteriochlorophylls↗
PubMed1993

[The significance of arterial redox potential measurement by Vincent's method in evaluating the hemorrhagic shock state of rabbits].

Previously we suggested that the arterial redox potential (ARp) is one of the most reliable indicators to evaluate the severity and outcome of the acutely-ill patients. In this study we attempted to clarify which redox system, intracellular or extracellular, is mainly represented by redox potentials measured from arterial blood in the hemorrhagic shock state rabbits. The arterial pyruvate/lactate, acetoacetate/beta-hydroxybutyrate and oxidized glutathione/reduced glutathione (GSSG/GSH) ratios were measured in hemorrhagic shock rabbits, and correlations between ARp and each of these factors were analyzed. The best correlation was found between ARp and P/L ratio. This indicates that ARp well reflects the cytosolic redox state, i.e. cytosolic [NAD+]/[NADH], and also [ATP]/[ADP][Pi] theoretically. The ARp is a valuable index in evaluating the shock state and can be easily measured with Vincent's method.

Animals↗
PubMed1975

Measurement of redox potential changes in anaerobic culture media caused by addition of blood.

A method has been described whereby the redox potential of unsealed and manipulated samples of solution can be determined. This method includes treating the platinum electrode with strong cleaning solution, adjusting the electrode with a culture of Proteus vulgaris in tryptic soy broth, and doing all manipulations inside a glove box that is continuously flushed with oxygen-free gas. This study has shown that prereduced media are much more reduced than media which have been dispensed only under a partial vacuum. It also has shown that addition of blood to prereduced medium does not eliminate the strongly reducing condition of the medium although there is a slight rise in redox potential.

Anaerobiosis↗
PubMed2005

A new device for measuring kinetics of ruminal pH and redox potential in dairy cattle.

A sampling and measuring device was set up to measure continuously the pH and the redox potential (Eh) of ruminal content in absence of any gaseous contamination (method 1). It was compared with a conventional suction device in which no precaution was taken to prevent air from coming into contact with the surface of collected samples (method 2). Two fistulated dry cows were used and fed a total mixed ration. Redox potential and pH measurements were performed repeatedly on collected samples using these 2 methods during a 9-h period; each period started 1 h before feeding. The partial pressure of oxygen (log fO2) was calculated from Nernst's equation using pH and Eh values. Results indicated that pH, Eh, and log f(O2) were affected by sampling method. In method 1, pH values ranged from 6.7 to 6.37 and Eh from -173.5 to -216.8 mV. In method 2, pH and Eh values varied, respectively, from 6.93 to 6.49 and from -111.3 to -139.5 mV. The partial pressure of oxygen was 10(6) times lower in samples that were continuously collected than in hand-samples. As a result, method 1 could make accurate measurements of pH and Eh of ruminal content.

Animals↗
PubMed2000

Photoinhibition as a function of the ambient redox potential in Tris-washed PS II membrane fragments.

The mode of photoinhibition as a function of the ambient redox potential (E(ambient)) in suspensions of Tris-washed PS II membrane fragments has been analyzed by monitoring flash-induced absorption changes at 830 nm. It was found: (a) the detectable initial amplitude, DeltaA (830) (total) , as a measure of the capacity to form the 'stable' radical pair, P680(+c) Q (A) (-c) , drastically decreases during a 10 min photoinhibition at E(ambient) values below +350 mV; (b) conversely, the normalized extent of the 18 mus relaxation kinetics, DeltaA (830) (18 mus) as a measure of the electron transfer from Y(Z) to P680(+c) becomes highly susceptible to light stress when E(ambient) exceeds values of about +350 mV; (c) effects of the ambient redox potentials are highly pronounced during light exposure under anaerobic conditions, while much smaller differences arise under aerobic conditions; (d) the extent of damage does not correlate with the total concentration of K(3)[Fe(CN)(6)] and K(4)[Fe(CN)(6)] in the suspension during photoinhibition but rather depends on the E( m )-values; (e) qualitatively similar features are observed when the redox buffer system K(3)[Fe(CN)(6)]/Na(2)S(2)O(4) is replaced by K(2)[IrCl(6)]/Na(2)S(2)O(4); (f) the characteristic E(ambient)-dependence of photoinhibition is observed only under anaerobic conditions. The results are discussed with respect to different redox components that might be involved, including brief comments on a possible role of Cyt b559.

Journal Article↗
PubMed2000

Redox potential is a determinant in the Escherichia coli anaerobic fermentative growth and survival: effects of impermeable oxidant.

Decrease of redox potential (Eh) down to -550-600 mV in the Escherichia coli culture is observed during growth in either anaerobic or aerobic conditions. The E. coli growth and survival under anaerobic fermentative conditions were found to be strongly inhibited by potassium ferricyanide in the concentration of 1 mM, when Eh was decreased to -50-100 mV. This oxidant also resulted in approximately 2-fold decrease of total and N,N'-dicyclohexylcarbodiimide (DCCD)-inhibited H+ efflux, 2.5-fold inhibition in K+ influx, 1.5-fold less K+ accumulation, and delayed a decrease in Eh to negative values by bacteria. K3[Fe(CN)6] was shown to block an ATP-dependent increase in the amount of accessible thiol groups of membrane vesicles that was inhibited by DCCD, and this inhibition by the oxidant could be recovered by dithiothreitol. These effects were not observed with cells growing under aerobic conditions. The effects of K3[Fe(CN)6], an impermeable oxidant, might be explained by the fact that redox potential is a determinant in the E. coli anaerobic fermentative growth and survival that has a regulatory role in maintaining H+ and K fluxes and the number of accessible thiol groups on membrane.

Dicyclohexylcarbodiimide↗
PubMed1997

Copper-62-ATSM: a new hypoxia imaging agent with high membrane permeability and low redox potential.

UNLABELLED: An ideal hypoxia imaging agent should have high membrane permeability for easy access to intracellular mitochondria and low redox potential to confer stability in normal tissue, but it should be able to be reduced by mitochondria with abnormally high electron concentrations in hypoxic cells. In this context, nitroimidazole residues are not considered to be essential. In this study, Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM), a 62Cu-bisthiosemicarbazone complex, with high membrane permeability and low redox potential, was evaluated as a possible hypoxia imaging agent, using electron spin resonance spectrometry and the Langendorff isolated perfused rat heart model as well as rat heart left anterior descending occlusion model. METHODS: Nonradioactive Cu-ATSM was incubated with rat mitochondria, after which reduction of Cu(II) to Cu(I) was measured with electron spin resonance. As a model of hypoxic mitochondria, rotenone (Complex I inhibitor)-treated mitochondria were used. RESULTS: In this study, Cu-ATSM was reduced by hypoxic but not by normal mitochondria. CONCLUSION: Thus, retention of 62Cu-ATSM was studied serially in perfused rat hearts under conditions of normoxia (95% O2 + 5% CO2), hypoxia (95% N2 + 5% CO2) and reoxygenation (95% O2 + 5% CO2). In normoxia and reoxygenation, 62Cu-ATSM injected as a single bolus showed low retention (23.77% and 22.80%, respectively) 15 min after injection, but retention was increased markedly under hypoxic conditions (81.10%). Also, in the in vivo left anterior descending occluded rat heart model, 62Cu-ATSM retention was inversely correlated with accumulation of 201Tl, a relative myocardial blood flow marker.

Animals↗
PubMed2000

Combined action of redox potential and pH on heat resistance and growth recovery of sublethally heat-damaged Escherichia coli.

The combined effect of redox potential (RP) (from -200 to 500 mV) and pH (from 5.0 to 7.0) on the heat resistance and growth recovery after heat treatment of Escherichia coli was tested. The effect of RP on heat resistance was very different depending on the pH. At pH 6.0, there was no significant difference, whereas at pH 5.0 and 7.0 maximum resistance was found in oxidizing conditions while it fell in reducing ones. In sub-lethally heat-damaged cells, low reducing and acid conditions allowed growth ability to be rapidly regained, but a decrease in the redox potential and pH brought about a longer lag phase and a slower exponential growth rate, and even led to growth failure (pH 5.0, < or =-100 mV).

Culture Media↗
PubMed1997

Photoinduced cyclic electron transfer in Rhodocyclus tenuis cells: participation of HiPIP or cyt c8 depending on the ambient redox potential.

We demonstrate the participation of a cytochrome c8 and a high-potential iron-sulfur protein (HiPIP) in the photoinduced electron transfer in whole cells of Rhodocyclus tenuis depending on the redox state or background continuous illumination. At high redox potentials (above 350 mV) or under a strong background illumination (5 W m-2), the cytochrome c8 acts as the physiological electron donor to the photo-oxidized high-potential hemes of the tetraheme cytochrome bound to the reaction center. For redox potentials ranging from 200 to 310 mV or under weak background illumination (1. 25 W m-2), the electron carrier is the HiPIP. The electron transfer between cyt c8 and HiPIP and the tetraheme cytochrome has half-times of 300 and 480 micros, respectively. A slow electrogenic phase of the membrane potential is linked to their rereduction. This phase is sensitive to a specific inhibitor of the cyt bc1 complex, indicating involvement of cyt c8 and HiPIP in the photoinduced cyclic electron transfer at these two redox conditions.

Absorption↗
PubMed1985

Amino acid sequence of high-redox-potential ferredoxin (HiPIP) isozymes from the extremely halophilic purple phototrophic bacterium, Ectothiorhodospira halophila.

The amino acid sequences of high-redox-potential ferredoxin (HiPIP) isozymes from Ectothiorhodospira halophila have been determined. These are: isozyme I, EPRAEDGHAHDYVNEAADPSHGRYQEGQLCENCAFWGEAVQDGWGRCTHPDFDEVLVKAEGWCSVYAPA S, and isozyme II, GLPDGVEDLPKAEDDHAHDYVNDAADTDHARFQEGQLCENCQFWVDYVNGWGYCQHPDFTDVLVRGEGW CSVYAPA. Isozyme II is the major form of HiPIP produced by the bacterium (65-80%) and is the most acidic of the known HiPIPs. The two isozymes are 72% identical to one another and require only a single residue deletion for alignment. Comparison of these HiPIPs with seven previously determined sequences revealed only 27% average identity. Both E. halophila HiPIP isozymes are likely to be functional since their sequences are equally distant from those of other species. The E. halophila HiPIP sequences show that H-bonding patterns recognized in Chromatium vinosum HiPIP are likely to be conserved and therefore cannot explain the unusually low redox potentials which have been reported.

Amino Acid Sequence↗
PubMed1998

Malate-aspartate shuttle, cytoplasmic NADH redox potential, and energetics in vascular smooth muscle.

The effect of inhibition of the malate-aspartate shuttle on the cytoplasmic NADH/NAD ratio and NADH redox state and its corresponding effects on mitochondrial energetics in vascular smooth muscle were examined. Incubation of porcine carotid arteries with 0. 4 mmol amino-oxyacetic acid an inhibitor of glutamate-oxaloacetate transaminase and, hence the malate-aspartate shuttle, inhibited O2 consumption by 21%, decreased the content of phosphocreatine and inhibited activity of the tricarboxylic acid cycle. The rate of glycolysis and lactate production was increased but glucose oxidation was inhibited. These effects of amino-oxyacetic acid were accompanied by evidence of inhibition of the malate-aspartate shuttle and elevation in the cytoplasmic redox potential and NADH/NAD ratio as indicated by elevation of the concentration ratios of the lactate/pyruvate and glycerol-3-phosphate/dihydroxyacetone phosphate metabolite redox couples. Addition of the fatty acid octanoate normalized the adverse energetic effects of malate-aspartate shuttle inhibition. It is concluded that the malate-aspartate shuttle is a primary mode of clearance of NADH reducing equivalents from the cytoplasm in vascular smooth muscle. Glucose oxidation and lactate production are influenced by the activity of the shuttle. The results support the hypothesis that an increased cytoplasmic NADH redox potential impairs mitochondrial energy metabolism.

Aminooxyacetic Acid↗
PubMed1981

The effect of redox potential on the kinetics of fluorescence induction in pea chloroplasts. I. Removal of the slow phase.

The effect of alteration of redox potential on the kinetics of fluorescence induction in pea chloroplasts has been investigated. Potentiometric titration of the initial (Fi) level of fluorescence recorded upon shutter opening gave a two component curve, with Em(*7) at -20 mV and -275 mV, almost, identical to results obtained using continuous low intensity illumination (Horton, P. and Croze, E. (1979) Biochim. Biophys. Acta 545, 188--201). The slow or tail phase of induction observed in the presence of DCMU can be eliminated by poising the redox potential at approx. 0 to +50 mV. At this potential Fi was increased by less than 10% and the higher potential quencher described above was only marginally reduced. The disappearance of the slow phase titrated as an n = 1 component with an Em(7) of +120 mV. Therefore it seems unlikely that the slow phase of fluorescence induction is due to photoreduction of the -20 mV quencher. These results are discussed with reference to current ideas concerning heterogeneity on the acceptor side of Photosystem II.

Chloroplasts↗
PubMed1998

[Effect of aeration and redox potential on the biosynthesis of the antibiotic imbricin].

The relationship between imbricin biosynthesis by Streptomyces imbricatus and the medium aeration and redox potential (Eh) was studied. The influence of the oxygen dissolution velocity within the ranges of 2.9 to 0.5 g O2/l.h was investigated and it was shown that the highest yield of the antibiotic was provided by the maximum velocity. At the background of the intensive aeration (2.9 g O2/l.h) decreasing of Eh by reducing agents such as ascorbic acid, L-thyrosin or K4Fe(CN)6 stimulated the biosynthesis whereas at the lower velocities the process proved to be inhibited. Under conditions of insufficient aeration the biosynthesis stimulation could be provided by increasing the medium Eh by acidifying agents such as K2Cr2O7, K3Fe(CN)6 or KMnO4. It was concluded that intensive synthesis of imbricin required not only efficient aeration but also definite levels of the medium redox potential.

Aerobiosis↗
PubMed2000

Protein redox potential measurements based on kinetic analysis with mediated continuous-flow column electrolytic spectroelectrochemical technique. Application to TTQ-containing methylamine dehydrogenase.

Kinetic determination of protein redox potentials with a mediated continuous-flow column electrolytic spectroelectrochemical technique (CFCESET) is described. In this method, the redox state of the mediator is completely regulated by the continuous-flow column electrolysis, and the homogeneous redox reaction between the mediator and a protein sample in the column is monitored spectroscopically at the downstream of the column. The protein/mediator reaction is in the pseudo-first-order kinetics, and then the rate equation is analytically solved. The kinetic analysis provides the protein redox potential as well as the homogeneous rate constant. In the kinetic measurements, equilibration of the system within the column is not required, which allows the use of increased kinds of mediators. This method was successfully applied to quinoprotein methylamine dehydrogenase containing tryptophan tryptophylquinone (TTQ) as a prosthetic group. The kinetic aspect is also valuable for the thermodynamic analysis with the mediated CFCESET. The half-life time of the kinetics can be utilized to optimize the system for the attainment of the equilibrated state within the column and can provide the assurance that the system is in equilibrium.

Electrochemistry↗
PubMed1976

Redox potential of plastoquinone A in spinach chloroplasts.

The redox potential of plastoquinone A in spinach chloroplasts was determined. The midpoint potential of the quinone is about +80 mV at pH 7.0 with an n value of 2. The pH-dependence of the potential is -30 mV per pH between pH 4.0 and 5.7, and -60 mV per pH between pH 5.7 and 8.0. The change of the slope at pH 5.7 is interpreted as the protonation of the oxidized plastoquinone A.

Borohydrides↗
PubMed2001

Synthesis, electrochemistry, and molluscicidal activity of nitroaromatic compounds: effects of substituents and the role of redox potential.

Abstract-Molluscicidal bioassays and electrochemical studies (measurement of first wave reduction potential, Epcl) were performed on several synthetic nitroaromatics, in relation to possible correlation between biological activity, redox potential and structural effects. Five of them presented a significant molluscicidal activity on Biomphalaria glabrata (LD50 < 20 ppm). The Epc1 values ranged from -0.532 to -0.857 V versus Ag/AgCl (0.1 M) (-0.260 to -0.585 V versus NHE), all of them, in the favorable range for reduction in vivo. Data comparison between Epc1 and molluscicidal activity indicates that the presence of the electroactive nitro group is important for the biological activity. Correlation with redox potential, however, was not evident. Structural effects seem to be the most important parameter. Higher activity is noticeable for phenols, including the para-nitro azo or hydrazo-containing compounds. No activity was observed for compounds having the benzylic substituent in meta position to the nitro group. These results suggest that activity undoubtedly involves more than reduction characteristics and that the possible formation of electrophilic species, after nitro reduction, can play an important role in molluscicidal activity against B. glabrata.

Animals↗
PubMedDate not supplied

[Effect of ligand orientation on the redox potential of homologous proteins].

Using experimental g-values of homologous cytochromes isolated from the horse heart and bacterial cyt-c-551 from Pseudomonas aeruginosa, the electron energy difference of redox-orbital of Fe(III) ion of heme was calculated during reduction. Data are in a good accordance with experimental redox-potential values for these proteins. The model gives opportunity to predict redox-potential values for other homologous proteins.

Animals↗