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At least 19 recordsLinked to original sources
PubMed1977

[Aqueous chloride and bromine solutions as disinfectants: composition, redox potential, differences of reactivity (author's transl)].

A method is given to calculate the equilibrium concentrations of the molecules and ions emerging from the hydrolysis and dissociation of chlorine and bromine in aqueous soltuion. The differing influence the pH value and the initial (total) halogene concentration exerts to the HOX- and X2-equilibrium concentration is discussed. From the calculated equilibrium concentrations and tabulated standard reduction potentials the redox potentials of chlorine and bromine solutions at various pH values are calculated. No correlation between the reactivity and the redox potential of the two halogens was observed. Two possible explanations for the differing reactivity of chlorine and bromine against proteins are presented.

Bromine↗
PubMed1978

Redox potentials of the photosynthetic bacterial cytochromes c2 and the structural bases for variability.

The cytochromes c2 of the Rhodospirillaceae show a much greater variation in redox potential and its pH dependence than the mitochondrial cytochromes c that have been studied. It is proposed that the range of redox potential for cytochromes c2 functioning as the immediate electron donor to photo-oxidised bacteriochlorophyll may be 345-395 mV at pH 5. Closely related cytochromes c2 with different redox potentials show patterns of amino acid substitution which are consistent with changes in hydrophobicity near the haem being at least a partial determinant of redox potential. More distantly related cytochromes are difficult to compare because of the large number of amino acid substitutions and the probability that there are subtle changes in overall peptide chain folding. The redox potential versus pH curves can be analysed in terms of either one ionisation in the oxidised form or two in the oxidised form and one in the reduced. The pK in the oxidised form at higher pH values can be correlated with the pK for the disappearance or shift of the near infrared absorption band located near 695 nm. The structural bases of these ionisations are not known but the possible involvement of the haem propionate residues is discussed.

Amino Acids↗
PubMed1976

[Effects of technological additives and heating range on some chemical and physical changes in canned meat. 2. Changes in redox potentials and selected quality characteristics].

The influence of technological additives and the range of heating on the redox potential, as well as on some quality features of canned meat was examined. The experiments showed, that the time of storage and the degree of heating of model preserves of meat influence on the redox potential. The technological additions as polyphosphates, ascorbic acid, gelatine and mixtures of these substances influence less on the redox potential. The analysis of each experimental factor showed, that on the secretion of meat juice occurring during can pasteurization or sterilization influence all experimental factors, as the kind of heating, the time of storage as well as the kind and the quantity of technological additives. The highest secretion of meat juice was found in cans with addition of ascorbic acid. Cans with addition of gelatine had the smallest content of jelly and consequently the lowest secretion of meat juice. It was also found a certain relation between the level of redox potential and the tested quality features of the model meat preserves.

Ascorbic Acid↗
PubMed1976

Determination of the redox potential of deazariboflavin by equilibration with flavins.

The redox potential of deazariboflavin has been determined for pH values from 5.5 to 9.2 by equilibration with riboflavin and lumiflavin 3-acetate. The position of the equilibrium with riboflavin was measured spectrophotometrically and fluorimetrically; the equilibrium potential with lumiflavin 3-acetate was measured spectrophotometrically and potentiometrically. The Em7 for deazariboflavin was found to be--0.273 +/- 0.003 V against the standard hydrogen electrode. Equilibrium with flavodoxin at pH 9.5 and 10.0 was also used to determine the redox potential of deazariboflavin at high pH values. The pK of dihydrodeazariboflavin was found from the break in the potential vs. pH diagram and from spectrophotometric pH titration. The pK value obtained by both methods is 7.00 +/- 0.05. We found that borate, a product of the reducing agent borohydride, complexed with the ribityl sidechain of deazariboflavin, causing a shift in the pK for the reduced form to values of about 8.

Flavins↗
PubMed1976

The size pH, and redox potential of the cecum in mice associated with various microbial floras.

Cecal size and in situ redox potential and pH of cecal contents were determined in conventionally reared mice and mice reared under a variety of gnotobiotic conditions: germfree, monoassociated with a cecal Clostridium sp., hexaflora-associated and thermoduric polyflora-associated. The mean Eh was approximately +200 mV in germfree and -200 mV in conventional mice. The Eh was close to zero in the monoassociated mice, thus occupying a position intermediate between the germfree and conventional mice. The potentials observed in the hexaflora and the thermoduric flora groups were indistinguishable from those of conventional animals. The degree of normalization was more advanced with respect to the redox potential than to the cecal size in the various gnotobiotic groups. In the thermoduric polyflora-associated group, normalization was observed in both cecal size and redox potential. This demonstrates that normalization can be accomplished with a relatively simplified microflora, at least with regard to the parameters studied.

Animals↗
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↗
PubMed2025

Decoding the distribution, structure-function-redox potential relationship and recent advances in fungal laccases: a systematic approach.

Laccases, categorized as multicopper oxidases, are recognized for their multifaceted roles in ecosystems and their utility in diverse industrial applications. Laccases from higher fungi, specifically Ascomycota and Basidiomycota, have garnered significant research interest due to their elevated redox potentials and their capacity to degrade lignin in decaying wood, alongside other industrial uses. Here, we have conducted a comprehensive and systematic analysis on fungal laccases using Web of Science, Scopus, PubMed, and ScienceDirect. The genomic distribution, phylogenetic affiliation, and structural organization of laccase-encoding genes in higher fungal species were investigated, as were the catalytic mechanisms of the corresponding enzymes. Additionally, the study explores the correlation between structural domains and redox potential, as well as the impact of post-translational modifications like glycosylation on enzyme activity. Furthermore, the recent advancements in laccase engineering, employing strategies such as rational design, directed evolution, and heterologous expression are discussed. The review also explores the scope of "artificial intelligence and machine learning" in deducing the structure-function relationships, optimizing codon usage, predicting signal peptides, enhancing enzymatic performance, and developing host-specific genetic engineering techniques is also discussed for tailoring fungal laccases to meet the demands of industrial biocatalysis for improved activity and stability.

Laccase↗
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↗
PubMed1979

Equilibrium and kinetic measurements of the redox potentials of cytochromes c2 in vitro and in vivo.

The equilibrium oxidation-reduction mipoint potential (Em) of isolated Rhodopseudomonas sphaeroides cytochrome c2 exhibits a pH-dependent behavior which can be ascribed to a pK on the oxidized form at pH 8.0 (Pettigrew et al. (1975) Biochim. Biophys. Acta 430, 197-208). However, as with mammalian cytochrome c (Brandt, K.G. Parks, P.C., Czerlinski, G.H. and Hess, G.P. (1966) J. Biol. Chem. 241, 4180-4185) this pK can more properly be attributed to the combination of a pK beyond pH 11, and a slow conformational change of the ferricytochrome. This has been demonstrated by resolving the Em of cytochrome c2 before and after the conformational change. The Em of the unaltered form is essentially pH independent between pH 7 and 11.5, and the lower equilibrium Em is due solely to the conformational change. In vivo the conformational change is prevented by the binding of the cytochrome c2 to the photochemical reaction center, and the cytochrome exhibits an essentially pH-independent Em from pH 5 to 11. The alkaline transition thus has little physiological significance, and it is unlikely that the redox reactions of cytochrome c2 in vivo involve protons.

Cytochrome c Group↗
PubMed1979

Characterization of two quenchers of chlorophyll fluorescence with different midpoint oxidation-reduction potentials in chloroplasts.

The properties of two redox quenchers of chlorophyll fluorescence in chloroplasts at room temperature have been investigated. (1) Redox titration of the fluorescence yield reveals two n = 1 components with Em7.8 at--45 and --247 mV, accounting for approx. 70 and 30% of the total yield, respectively. (2) Neutral red, a redox mediator often used at redox potentials below --300 mV, preferentially quenches the fluorescence controlled by the --247 mV component. Titrations using neutral red artifactually create an n = 2 quenching component with Em7.8 = --375 mV. (3) Analysis of fluorescence induction curves recorded at different redox potentials indicates that both the --45 and --247 mV components can be photochemically reduced. The reduction of the --247 mV component corresponds to a fast phase of the induction curve whilst the slower reduction of the 45 mV component accounts for the tail phase. (4) The excitation spectra for the fluorescence controlled by the two quenchers show small differences in the ratio of chlorophyll a and b. (5) Whereas the --247 mV component readily shows a 60 mV per pH unit dependency on solution pH, the ability of the --45 mV component to respond to pH change is restricted. (6) Triton Photosystem II particles contain both quenchers but the --247 mV component accounts for approx. 70% of the fluorescence and the high component has an Em7.8 of +48 mV. The relative merits of sequential and parallel models in explaining the presence of the two quenchers are considered.

Chlorophyll↗
PubMed1976

Methionine sulfoxide cytochrome c.

Cytochrome c has been chemically modified by methylene blue mediated photooxidation. It is established that the methionine residues of the protein have been specifically converted to methionine sulfoxide residues. No oxidation of any other amino acid residues or the cysteine thioether bridges of the molecule occurs during the photooxidation reaction. The absorbance spectrum of methionine sulfoxide ferricytochrome c at neutrality is similar to that of the unmodified protein except for an increase in the extinction coefficient of the Soret absorbance band and for the complete loss of the ligand sensitive 695 nm absorbance band in the spectrum of the derivative. The protein remains in the low spin configuration which implies the retention of two strong field ligands. Spin state sensitive spectral titrations and model studies of heme peptides indicate that the sixth ligand is definitely not provided by a lysine residue but may be methionine-80 sulfoxide coordinated via its sulfur atom. Circular dichroism spectra indicate that the heme crevice of methionine sulfoxide ferri- and ferrocytochrome c is weakened relative to native cytochrome c. The redox potential of methionine sulfoxide cytochrome c is 184 mV which is markedly diminished from the 260 mV redox potential of native cytochrome c. The modified protein is equivalent to native cytochrome c as a substrate for cytochrome oxidase and is not autoxidizable at neutral pH but is virtually inactive with succinate-cytochrome c reductase. These results indicate that the major role of the methionine-80 in cytochrome c is to preserve a closed hydrophobic heme crevice which is essential for the maintainance of the necessary redox potential.

Amino Acids↗
PubMed1977

Mitochondrial and cytosolic NADPH systems and isocitrate dehydrogenase indicator metabolites during ureogensis from ammonia in isolated rat hepatocytes.

1. Citrate isocitrate and 2-oxoglutarate levels were determined in isolated rat hepatocytes and in particulate and soluble fractions, thereof, obtained by the digitonin and silicone oil fractionation technique. 2. Caculated from isocitrate/2-oxoglutarate ratios ("indicator metabolite method"), the redox potential of mitochondrial free NADPH is -402 mV, whereas that of the extramitochondrial (cytosolic) space is about 10 mV more positive, -392 mV. 3; Addition of ammonia (either as ammonium chloride or from urea plus urease) to isolated hepatocytes causes preferential oxidation of mitochondrial NADPH, is demonstrated by spectrophotometry of the dihydro band and by the changes in the isocitrate/2-oxoglutarate ratios. The redox potential difference of free NADPH between mitochondria and cytosol is abolished or even reserved. 4. It is concluded that during urogenesis from ammonia mitochondrial isocitrate oxidation is shifted largely in favor of the NADP-linked as opposed to the NAD-linked enzyme; isocitrate concentration under these conditions is less than 10 muM, below the Km (isocitrate) of the NAD-linked enzyme but in the range of that for the NADP-linked enzyme. 5. Both in the absence and in the presence of ammonia there is a concentration gradient across the mitochondrial inner membrane (from mitochondria to cytosol) for citrate, isocitrate, and also, to a smaller extent, for 2-oxoglutarate. 6. These results and data in the literature on enzyme activity are in agreement with the assumption of near-equilibrium of NADP-dependent isocitrate dehydrogenases in the mitochondrial matrix and cytosolic spaces in the absence of ammonia; accordingly, during urea formation from added ammonia the redox potential of mitochondrial free NADPH is increased to -391 mV or possibly even higher if there exists an indicator error under this condition.

Ammonia↗
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↗