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At least 883 records · Page 49Linked to original sources
PubMed1994

Type-2 astrocytes have much greater susceptibility to heat stress than type-1 astrocytes.

The present investigations were undertaken to examine the susceptibility of type-2 astrocytes to elevated temperature. Type-2 astrocytes are much more easily injured by temperature elevation than type-1 astrocytes. This may be related to cellular redox potential. Type-1 astrocytes have a greater cytosolic NAD redox potential (i.e., higher NADH:NAD levels) than type-2 astrocytes as evidenced by a 9-fold higher ratio of lactate to pyruvate released into the medium by type-1 astrocytes than type-2 astrocytes. Heat stress causes the induction of hsp-72 in both type-2 and type-1 astrocytes; however, hsp-72 protein expression is retained for a longer period of time by the type-2 astrocyte. A possible basis for the greater sensitivity of type-2 astrocytes to stress may be a poorer ability to scavenge free radicals. This differential sensitivity of one neural cell type relative to another to elevated temperature may be of significance in understanding the effects of hyperthermia on the developing brain.

Animals↗
PubMed1987

Mutagenicity of nitracrine analogues in Salmonella typhimurium: mutational specificity and activation by bacterial enzymes and rat-liver S9.

The mutagenic potential of 9-[(3-dimethylaminopropyl)amino]-acridine and its 1-(nitracrine), 2-, 3- and 4-nitro derivatives was studied in several strains of Salmonella typhimurium, using a plate-incorporation assay. In view of the potential importance of DNA binding and nitro group reduction, binding constants and redox potentials were determined. The parent compound was mutagenic only in the frameshift tester strain TA1537, and this effect was not enhanced by the plasmid pKM101. Each of the nitroarenes showed significant activity in S. typhimurium strains TA1537 and TA1538, and this mutagenicity was enhanced by the presence of plasmid pKM101. All caused reversion of the base-pair substitution allele in hisG46 in strain TA100 and this effect was either largely or totally dependent upon the plasmid. The frameshift mutagenic effects of the 3-nitro and 4-nitro compounds appeared to be little dependent upon the classical nitroreductase which is deficient in strain TA98NR, or transacetylase enzyme lacking in strain TA98/1,8-DNP6, whereas the activity of the 1-nitro compound depended partly on that nitroreductase enzyme, and that of the 2-nitro compound on having both activities present. In the latter two cases, the mutagenic effects of the compounds could not be restored by the addition of an S9 mix of mammalian enzymes. Mutagenicity data were compared with physicochemical parameters. The results do not distinguish between the view that the orientation of the nitro group with respect to the aromatic plane dictates mutagenic potential, and the earlier view that the nitro group redox potential is important. However, the extraordinary mutagenic potency of the 1-NO2 derivative is not explainable by its physicochemical properties alone.

Aminoacridines↗
PubMedDate not supplied

Multiple mechanisms in hepatic microsomal azoreduction.

1. Microsomal reduction of azo dyes related to dimethylaminoazobenzene (DAB) is catalysed by at least two types of cytochrome P-450. The first is selectively induced by clofibrate. The second is induced by phenobarbital, beta-naphthoflavone, isosafrole, and pregnenolone-16 alpha-carbonitrile, as well as clofibrate. 2. Azoreduction by the first type of P-450 is insensitive to both O2 and CO and involves dyes with only electron-donating substituents (I substrates). 3. Azoreduction by the second type of P-450 is inhibited by both O2 and CO and involves dyes with electron-withdrawing as well as donating substituents (S substrates). 4. All azo dye substrates exhibit two negative and one positive redox potential, as measured anaerobically by cyclic voltammetry. The negative potentials reflect one- and two-electron reductions while the positive potential permits electron transfer from microsomal P-450, the redox potential for which is reported to be negative (approximately 0.35 V). The positive potential is associated with a polar electron-donating group para to the azo linkage, which is an absolute requirement for microsomal reduction. Dyes without this functional group do not exhibit positive potentials and are not reduced. 5. The first negative potential of S substrates is quenched upon admitting air to the system, whereas this potential is unaffected in I substrates. The relative stability of the one-electron reduced state may be an explanation for the differential O2 sensitivity of I and S substrate reduction.

Animals↗
PubMed1987

Oxidation-reduction potential studies: a new method in pharmacology principles, materials, and methods.

Oxidation-reduction (redox) potential measurement is not used in pharmacology at the present time. However, it represents a physicochemical parameter that may be as important as the other currently used physicochemical parameters, such as pH and pKa. Redox potential variations include conformational modifications that may influence bioavailability of drugs. We report here an original and convenient equilibrium method to determine this potential in biological fluids, especially in blood.

Female↗
PubMed1980

Effects of surface potential on the equilibrium and kinetics of redox reactions of membrane components with external reagents in chromatophores from Rhodopseudomonas sphaeroides.

The characteristics of the salt and pH dependences of the redox levels of cytochrome c2 and reaction center bacteriochlorophyll were studied in chromatophores from Rhodopseudomonas sphaeroides. They could be explained in terms of the difference of redox potential in the membrane from that in the bulk aqueous phase due to the electrostatic potential difference arising from charges fixed on the membrane surface. The midpoint potentials (Em) became lower when the surface potential (the electrostatic potential at the surface with reference to the bulk aqueous phase) had large negative values at lower salt concentrations at neutral pH, as predicted by the Gouy-Chapman theory. The rate of oxidation of cytochrome c2 in chromatophores by ferricyanide also depended on salt and pH levels. The rate was low at low salt concentrations, probably because of the lower surface concentration of ferricyanide compared with the bulk concentration, due to the surface potential.

Bacterial Chromatophores↗
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↗
PubMed1988

Effect of nitrate and its reduction products on the growth and activity of the rumen microbial population.

1. The nature of the digestion-inhibiting substance in Kikuyu grass (Pennisetum clandestinum, Hochst), containing high levels of nitrate, was investigated using in vitro digestibility techniques. 2. Nitrite, which accumulated during the reduction of nitrate to ammonia, seemed to be the primary factor reducing digestibility. Nitrate and ammonia did not affect digestion in vitro. 3. Nitrite caused a reduction in the cellulolytic, xylanolytic and total microbial population, with a concomitant reduction in cellulase and xylanase activity of the digesta. 4. The mode of action of nitrite on rumen microbial growth was investigated. 5. The possibility that the growth of cellulolytic rumen microbes was depressed by a reduction in concentration of essential branched-chain volatile fatty acids by nitrite was discounted. 6. Although nitrite caused a marked increase in the redox potential, due to its oxidizing properties, the more-positive redox potential did not reduce the digestibility of the grass. 7. The growth of three of the four major cellulolytic bacteria commonly found in the rumen was severely depressed by nitrite, while some rumen bacteria were relatively insensitive to nitrite. 8. Growth inhibition seemed to depend primarily on the extent to which these microbes derive their energy from electron-transport-mediated processes. 9. It was suggested that, due to the sensitivity of some rumen bacteria to nitrite, digestibility and therefore animal performance could be affected long before clinical symptoms of nitrite toxicity become apparent.

Animals↗
PubMed1975

An analysis of the drugs acting on cerebral energy metabolism.

The behaviour of (a) the redox potential of the lactate/pyruvate system and the changes of the redox potential of the lactate/pyruvate system across the brain; (b) the energy charge potential of the adenylate pool, was studied in the brain of curarized beagle dogs. The influence of certain drugs (amobarbital, nicergoline, theophylline, papaverine, bamethan, dipyridamole, bemegride) on these parameters was evaluated under control conditions, during hypoxemia and during post-hypoxiemic recovery. On the whole, the action on energetic metabolism appears to be unrelated to the action believed to be exerted by drugs on cerebral vessels.

Adenine Nucleotides↗
PubMed1994

Lactate monooxygenase. I. Expression of the mycobacterial gene in Escherichia coli and site-directed mutagenesis of lysine 266.

Lactate monooxygenase utilizes oxygen in the conversion of L-lactate to acetate, CO2, and water. The gene for the enzyme from Mycobacterium smegmatis had been cloned into Escherichia coli (Giegel, D. A., Williams, C. H., Jr., and Massey, V. (1990) J. Biol. Chem. 265, 6626-6632) and the derived amino acid sequence compared to glycolate oxidase and flavocytochrome b2, enzymes of known three-dimensional structure (Lindqvist, Y., and Brändén, C. I. (1989) J. Biol. Chem. 264, 3624-3628; Xia, Z. X., and Mathews, S. F. (1990) J. Mol. Biol. 212, 837-863). There is strong homology, especially around residues in the active site. The mechanism proposed for lactate monooxygenase involves an intermediate having a negative charge at the N(1)-position of the FMN. Based on the homology, lysine 266 is the residue suggested to neutralize that charge. Wild type enzyme and several forms of the enzyme altered at active site residues by site-directed mutagenesis have been expressed in E. coli and purification procedures developed. The properties determined for the recombinant wild type enzyme were, in every case, the same as those previously determined for the enzyme isolated from M. smegmatis. Mutation of lysine 266 to a methionine created K266M. The semiquinone showed spectral features different from those found in the wild type enzyme and was no longer thermodynamically stable. This indicates a redox potential for the enzyme-bound semiquinone/reduced flavin couple that is higher than the midpoint potential for the oxidized flavin/semiquinone couple. The two-electron redox potential was determined to be -180 mV at 25 degrees C, pH 7.0. In wild type enzyme, attack of the flavin ring by sulfite creates a negative charge at the FMN N(1)-position. In K266M, the stabilization of the sulfite adduct was 17,000-fold weaker (Kd approximately 10(-3) M) than in the wild type enzyme, with a rate of association that is lowered by 10,000-fold (kon = 1.2 M-1 s-1). The rate of reduction with L-lactate is significantly decreased in K266M. Unexpectedly, binding of substrate and inhibitors is significantly weaker in K266M than in the wild type enzyme. In all properties involving a negative charge at position N(1) of the FMN, K266M is distinctly different from wild type enzyme. This makes it quite likely that lysine 266 serves the postulated role of interacting with this negative charge.

Amino Acid Sequence↗
PubMed2004

Effect of structure on the reduction potentials of films of constitutional isomers of iron-sulfur cluster core dendrimers.

The thermodynamic redox potentials of films of constitutional isomers of iron-sulfur cluster core dendrimers were measured and compared. It was determined that the primary structure of the dendrimer influences its reduction potential. Dendrimers containing so-called backfolded linkages were more difficult to reduce than their extended analogues. This behavior is rationalized by suggesting that the backfolded isomers pack more tightly around the iron-sulfur cluster, creating a more hydrophobic local microenvironment. Also, all of these molecules are easier to reduce in the film than in dimethyl formamide solution. The variation in redox potential between film and solution environment was compared to that of dendrimers of differing generations and correlated with the amount of hydrophobic dendron surrounding the cluster.

Journal Article↗
PubMed2000

Eukaryotically encoded and chloroplast-located rubredoxin is associated with photosystem II.

We analyzed a eukaryotically encoded rubredoxin from the cryptomonad Guillardia theta and identified additional domains at the N- and C-termini in comparison to known prokaryotic paralogous molecules. The cryptophytic N-terminal extension was shown to be a transit peptide for intracellular targeting of the protein to the plastid, whereas a C-terminal domain represents a membrane anchor. Rubredoxin was identified in all tested phototrophic eukaryotes. Presumably facilitated by its C-terminal extension, nucleomorph-encoded rubredoxin (nmRub) is associated with the thylakoid membrane. Association with photosystem II (PSII) was demonstrated by co-localization of nmRub and PSII membrane particles and PSII core complexes and confirmed by comparative electron paramagnetic resonance measurements. The midpoint potential of nmRub was determined as +125 mV, which is the highest redox potential of all known rubredoxins. Therefore, nmRub provides a striking example of the ability of the protein environment to tune the redox potentials of metal sites, allowing for evolutionary adaption in specific electron transport systems, as for example that coupled to the PSII pathway.

Biological Transport↗
PubMed2003

An amperometric biosensor for glucose based on electrodeposited redox polymer/glucose oxidase film on a gold electrode.

In this paper, we described a glucose biosensor based on the co-electrodeposition of a poly(vinylimidazole) complex of [Os(bpy)2Cl](+/2+) (PVI-Os) and glucose oxidase (GOX) on a gold electrode surface. The one-step co-electrodeposition method provided a better control on the sensor construction, especially when it was applied to microsensor construction. The modified electrode exhibited the classical features of a kinetically fast redox couple bound to an electrode surface and the redox potential of the redox polymer/enzyme film was 0.14 V (vs. SCE). For a scan rate of up to 200 mV s(-1), the peak-to-peak potential separation was less than 25 mV. In the presence of glucose, a typical catalytic oxidation current was observed, which reached a plateau at 0.25 V (vs. SCE). Under the optimal experimental conditions, the steady-state electrooxidation current measured at 0.30 V (vs. SCE) was linear to the glucose concentration in the range of 0-30 mM. Successful attempts were made in blood sample analysis.

2,2'-Dipyridyl↗
PubMed2005

Sulphur partitioning in sediments and biodeposits below mussel rafts in the Ria de Arousa (Galicia, NW Spain).

Forty four core samples were analyzed to determine sediment particle size, total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen and total sulphur. Sequential extraction of S was also carried out, differentiating AVS (acid volatile sulphide), elemental S, organic S and pyrite S. The results obtained show that the presence of mussel rafts causes intense changes in the physicochemical composition and properties of the sea floor in the Ria de Arousa. The percentage of silt and clay, TOC, TIC and total N were significantly higher in the biodeposit than in the sediment. In contrast, there were no differences between the biodeposit and the sediment in terms of pH (8.0-8.7) and redox potential. The sediment and biodeposit were always anoxic, with values of redox potentials below -100 mV. In accordance with these conditions, the dominant fraction of S was pyrite S (FeS(2)). The AVS fraction and elemental S were present at low concentrations, except in the uppermost part of each core. Pyrite was relatively stable when the biodeposit and sediment were maintained in suspension for 8 days in oxic sea water; unlike the AVS fraction, which disappeared within a few hours.

Analysis of Variance↗
PubMed2005

Embryopathy in experimental diabetic gestation: assessment of oxidative stress and antioxidant defence.

Maternal diabetes is associated with an increased rate of congenital fetal anomaly. In the present study, diabetes was induced by streptozotocin in female rats one week prior to conception and the embryos were examined during organogenesis. Experimental diabetes is associated with over-production of free radicals and disturbed antioxidant defence, particularly in malformed embryos. Oxidative stress is demonstrated by increased MDA accumulation and reduced glutathione levels. Despite large differences in the reduced/oxidised glutathione ratios during organogenesis in the control, diabetic non-malformed and malformed embryo groups, the half-cell redox potential was constant for each group during the experimental period. Calculated redox potentials indicated that although embryo cells from the control and diabetic mother groups were of the same chronological age, the stages of development were different. Increased oxidative stress in rat embryos was associated with increased glutathione peroxidases and glutathione-S-transferase activity. This may, in part, provide an explanation for the observed accumulation of oxidised glutathione in malformed embryos. Moreover, decreased levels of vitamin C and selenium were observed. Increased oxidative stress and perturbations in antioxidant defence contribute to the high incidence of congenital anomalies in experimental diabetic gestation.

Animals↗
PubMed2001

Polyionic fusion peptides function as specific dimerization motifs.

The de novo design of a molecular adapter for directed association and covalent linkage of two polypeptides is presented. Using peptides containing charged amino acid residues and an additional cysteine residue (AlaCysLys(8) and AlaCysGlu(8)) we demonstrate that the electrostatic interaction promotes the association of two synthetic peptides and, subsequently, disulfide bond formation. The reaction depends on both the redox potential and on the ionic strength of the buffer. Varying the redox potential, the interaction of the peptides was quantified by a Delta G(0') of 6.6 +/- 0.2 kcal/mol. Heterodimerization of the peptides is highly specific, a competition of association by other cysteine containing compounds could not be observed. Two proteins comprising cysteine-containing polyionic fusion peptides, a modified Fab fragment and an alpha-glucosidase fusion, could be specifically conjugated by directed association and subsequent disulfide bond formation. Both proteins retain their functional characteristics within the bifunctional conjugate: enzymatic activity of the alpha-glucosidase and antigen-binding capacity of the Fab fragment are equivalent to the non-conjugated components.

Animals↗
PubMed2006

The synechocystis sp PCC 6803 oxa1 homolog is essential for membrane integration of reaction center precursor protein pD1.

Synechocystis sp PCC 6803 Slr1471p, an Oxa1p/Alb3/YidC homolog, is an essential protein for cell viability for which functions in thylakoid membrane biogenesis and cell division have been proposed. Using a fusion of green fluorescent protein to the C terminus of Slr1471p, we found that the mutant slr1471-gfp is photochemically inhibited when light intensities increase to 80 micromol x m(-2) x s(-1). We show that photoinhibition correlates with an increased redox potential of the reaction center quinone Q(A)(-) and a decreased redox potential of Q(B)(-). Analysis reveals that membrane integration of the D1 precursor protein is affected, leading to the accumulation of pD1 in the membrane phase. We show that Slr1471p interacts directly with the D1 protein and discuss why the accumulation of pD1 in two reaction center assembly intermediates is dependent on Slr1471p.

Bacterial Proteins↗
PubMed1992

NMR and EPR studies on a monoheme cytochrome c550 isolated from Bacillus halodenitrificans.

A c-type monoheme ferricytochrome c550 (9.6 kDa) was isolated from cells of Bacillus halodenitrificans sp.nov., grown anaerobically as a denitrifier. The visible absorption spectrum indicates the presence of a band at 695 nm characteristic of heme-methionine coordination. The midpoint redox potential was determined at several pH values by visible spectroscopy. The redox potential at pH 7.6 is 138 mV. When studied by 1H-NMR spectroscopy as a function of pH, the spectrum shows a pH dependence with pKa values of 6.0 and 11.0. According to these pKa values, three forms designated as I, II and III can be attributed to cytochrome c550. The first pKa is probably associated with protonation of the propionate groups. The second pKa value introduces a larger effect in the 1H-NMR spectrum and is probably due to the ionisation of the axial histidine. Studies of temperature variation of the 1H-NMR spectra for both the ferrous and ferri forms of the cytochrome were performed. Heme meso protons, the heme methyl groups, the thioether protons, two protons from a propionate and the methylene protons from the axial methionine were identified in the reduced form. The heme methyl resonances of the ferri form were also assigned. EPR spectroscopy was also used to probe the ferric heme environment. A signal at gmax approximately 3.5 at pH 7.5 was observed indicating an almost axial heme environment. At higher pH values the signal at gmax approximately 3.5 converts mainly to a signal at g approximately 2.96. The pKa associated with this change is around 11.3. The N-terminal sequence of this cytochrome was determined and compared with known amino acid sequences of other cytochromes.

Amino Acid Sequence↗