Oxidation-reduction states

Oxidation-reduction titrations revealed the existence of two other oxidation-reduction states, EPR silent, designated as Ni-Si (Ni-Si-lent) and Ni-R (Ni-Reduced) (178, 180). A detailed study of the oxidation-reduction pattern involved enabled the following sequence of events (in the oxidation direction) to be written ... 

Throughout this book a major stress is on catalysis in organisms. Catalysis is confined to non-metals and metal ions of attacking power, either as Lewis acids or in oxidation/reduction and this excludes the simplest ions such as Na+, K+ and Ca2+ (and Cl- among anions). The transition metal ions and zinc are the most available powerful catalysts. The metals in a transition series are known to have selective binding properties, exchange rates and oxidation/reduction states, which can be put to use in catalysis in quite different ways (Table 2.13). It is noticeable that especially the complexes of metal elements... 

Criaud, A., C. Fouillac and B. Marty, 1989, Low enthalpy geothermal fluids from the Paris basin, 2 - oxidation-reduction state and consequences for the prediction of corrosion and sulfide scaling. Geothermics 18, 711-727. 

Vermilion, J.L. and Coon, M.J. (1978) Purified liver microsomal NADPH-cytochrome P-450 reductase. Spectral characterization of oxidation-reduction states. Journal of Biological Chemistry, 253 (8), 2694-2704. 

Surface fluorescence of NADH/NADPH can be recorded continuously with a DC fluorimeter and correlated with changes in experimental conditions. A mercury arc lamp (with a 340-375 nm filter in front) is used as a hght source for fluorescence excitation. The fluorescence response of reduced NADH/NADPH was measured at 450-510 nm. The DC fluorimeter and the Hg arc lamp are connected to the kidney by a trifurcated fiber optics light guide. NADH/NADPH fluorescence emission can be corrected for changes in tissue opacity by a 1 1 subtraction of reflectance changes at 340-375 nm from the fluorescence. To determine NADH/NADPH redox state of the total surface area of kidney cortex and to evaluate whether certain areas were insufficiently perfused, fluorescence photographs of the total surface area were taken. The study demonstrated that the surface fluorescence method is simple and provides specific information about the mitochondrial oxidation-reduction state. 

Mitochondrial oxidation-reduction state, NADH/NADPH SURFACE FLUORESCENCE IN LIVING TISSUES MITOGEN-ACTIVATED PROTEIN KINASE... 

It is remarkable that the nitrogen cycle employs extreme oxidation-reduction states of nitrogen. Nitrification carries N from 3 to 5, whereas denitrification reduces N from 5+ to 0. A more direct cycle using only redox states of N between... 

On the other hand, Feigelson and his associates169,170,172-175 have reported that not only heme but also copper is an essential cofactor in both Pseudomonad and hepatic enzymes and that there are three different oxidation-reduction states of the enzyme, namely, a fully reduced form, E(Cu+, Fe2+) a half-reduced form, E(Cu+, Fe3+) or its valence isomer E(Cu2+, Fe2+) and a fully-oxidized form,... 

The Fe atoms of the cytochromes undergo oxidation and reduction during respiration, cycling between the ferrous (Fe2+) and ferric (Fe3+) oxidation states. The absorption spectra of the oxidized and reduced forms differ (fig. 14.4). In the 1930s, David Keilin used this property to measure the oxidation-reduction states of cytochromes in living cells. Under anaerobic conditions, the cytochromes rapidly became reduced in the presence of 02, they became oxidized. Certain molecules that inhibited respiration (CO, N3, or CN ) blocked the oxidation other inhibitors (amy-tal, rotenone, and malonate) blocked the reduction. Keilin found that the transfer of electrons from cytochrome c to 02... 

The second proton transfer mechanism involves protonation of carboxyl or histidyl groups associated with electron carriers in the membrane and release of protons from these sites through proposed channels when the electron carrier is oxidized. This is essentially a proton channel system with movement through the channel gated by the oxidation-reduction state of the prosthetic group on the electron transport protein. The classical example of this is seen in cytochrome c oxidase (Figure 3). 

Kushnareva Y, Murphy AN, Andreyev A (2002) Complex i-mediated reactive oxygen species generation Modulation by cytochrome c and nad(p)(+) oxidation-reduction state. Biochem J 368 545-553... 

Answer As shown in Figure 19-6, the oxidation-reduction state of the carriers in the electron-transfer system varies with the conditions. 

Redox titrations involve determination of equilibrium between the enzyme and a redox agent of known redox potential. The method requires a redox agent with redox potential close to the protein of interest, to ensure reversibility. The protein is exposed to different concentrations of the redox agent, and once equilibrium is attained, the half cell potential is measured with electrodes and the oxidation-reduction state of the proteins is measured by some physical technique, usually UV-Vis spectrophotometry. The concentration of the oxidized and reduced forms is determined at isosbestic points, and thus spectral characterization of redox species (ferric enzyme,... 

While the redox titration method is potentiometric, the spectroelectrochemistry method is potentiostatic [99]. In this method, the protein solution is introduced into an optically transparent thin layer electrochemical cell. The potential of the transparent electrode is held constant until the ratio of the oxidized to reduced forms of the protein attains equilibrium, according to the Nemst equation. The oxidation-reduction state of the protein is determined by directly measuring the spectra through the tranparent electrode. In this method, as in the redox titration method, the spectral characterization of redox species is required. A series of potentials are sequentially potentiostated so that different oxidized/reduced ratios are obtained. The data is then adjusted to the Nemst equation in order to calculate the standard redox potential of the proteic species. Errors in redox potentials estimated with this method may be in the order of 3 mV. 

Redox potential is the measure of the oxidation-reduction state of a soil, and is determined by redox reactions involving the transfer of electrons from one chemical species to another. A generalized redox reaction can be written as... 

Figure 9. Multicolor performance of conducting PANi at different oxidation/reduction states.

F. E. Sulphide and carbonate equilibrium and the oxidation-reduction state of sulfur in the mineral regions of the Crimean mineral waters. Dokl. Akad. Nauk. SSSR 142(1) (1962). 

Petronilli, V., Costantini, P., Scorrano, L., Colonna, R., Passamonti, S., and Bemardi, P. (1994). The voltage sensor of the mitochondrial permeability transition pore is tuned by the oxidation-reduction state of vicinal thiols. Increase of the gating potential by oxidants and its reversal by reducing agents. J Biol Chem 269, 16638 2. 

The oxygen evolving system is referred to as a clock because it involves five oxidation-reduction states that must be completed in order. 

The dependence of the electrical resistivity of chromic oxide on the oxidation-reduction state of the surface has been investigated. The resistivity of oxidized chromia at 500 varies with the total excess oxygen according to the relation p = On addition of hydrogen at 500 ... 

R.J. Paul, FI. Schneckenburger, Oxygen concentration and the oxidation-reduction state of yeast Determination of free/bound NADH and flavins by time-resolved spectroscopy, Naturwissenschaften 83, 32-35 (1996)... 

Predict the oxidation-reduction states of NAD", NADH-Q reductase, ubiquinone, cytochrome Cl, cytochrome c, and cytochrome a in liver mitochondria that are amply supplied with isocitrate as substrate, Pj, ADP, and oxygen but are inhibited by... 

Besides the iron concentration, a wine s oxidation-reduction state and the possible presence of oxidation catalysts are also involved. The quantity of soluble complexes with organic acids, i.e. iron that is not involved in the casse mechanism, is also significant. This factor is, however, impossible to measure. 

Once the appropriate dose has been established, the entire batch of wine can be treated. It is essential that it should be in the same oxidation-reduction state as the sample used for the preliminary trial. Treatment should therefore take place shortly after the test and the wine must not be handled in the meantime. If the wine to be treated is kept in several containers, separate trials must be carried out for each one. 

The forms and concentration of selenium in the soil solution are governed by various physical-chemical factors expressed in terms of chemical ligands, pH, dissociation constants, solubility products, and oxidation-reduction states. In acid soils (pH 5-6.5), selenium is usually bound as a basic ferric selenite of extremely low solubility and is essentially unavailable to plants. In alkaline soils (pH 7.5-S.5), selenium may be present as selenate ions and become water soluble. 

Horok V, Gillette JR (1971) A Study of the Oxidation-Reduction State of Synthetic 3,4-Dihydroxy-DL-phenylalanin Melanin. Molec Pharmacol 7 429... 

Manipulation in the analysis of biological samples (plasma, urine, tissue samples) is designed to decrease the amount of protein and other interfering material, and it may be necessary also to control the oxidation/reduction state of the vitamin. The chemical characteristics of the vitamins (Table 1) are of... 

Lehninger AL, Vercesi A, Bababunmi EA (1978) Regulation of Ca " release from mitochondria by the oxidation-reduction state of pyridine nucleotides. Proc Natl Acad Sd USA 75 1690-1694... 

Chance, B., Cohen, M., JObsis, F. F., and Schoener, B., 1962, Intracellular oxidation reduction states in vivo, Science 137 449-508. 

In selective inhibition, the electron transport chain is blocked with specific inhibitors, and the oxidation-reduction states of the components below and above the block are studied. Those below the block are reduced, and those above the block are oxidized. The kinetic studies are based on the assumption that the sequence of the spectrophotometric changes resulting from the oxidation and reduction of each component of the electron transport chain reflects the sequence of the chemical reactions. On the basis of such spectrophotometric studies on phosphorylating particles, intact mitochondria, and intact cells, the following sequence has been obtained NADH, cytochrome b, cytochrome Cj, cytochrome c, cytochrome a, cytochrome a3, O2. 

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