Effect Of Redox State Research Articles

Redox‐Independent Low Water Solubility in Quartz and Implications for Water Storage in the Crust

AbstractQuartz is an important mineral constituent of the continental crust, which commonly contains trace amounts of water as hydroxyl in the lattice. Despite considerable efforts to document the roles of pressure, temperature, and chemistry on water storage in quartz, the effect of redox state, a key thermodynamic factor in Earth sciences, has not been well established. We assessed the redox effect on water solubility in quartz at 2 and 10 kbar and 800°C, by equilibrating two natural gem‐quality crystals with water over a range of redox conditions. Recovered samples show infrared absorption bands at 3,100–3,600 cm−1. Dehydration experiments at 1200°C (room pressure) suggest that the two bands at ∼3,197 and 3,293 cm−1 are linked to Si‐O overtones, with the other bands to hydroxyl. The water solubility, ∼3.7–32.2 ppm wt. H2O, is redox‐independent, differing from other minerals such as feldspar, pyroxenes, garnet, rutile, and olivine in which the water solubility is significantly redox‐dependent. This provides evidence that the water incorporation in quartz is not controlled by polyvalent elements and/or other redox‐linked mechanisms. Considering the roles of Al, Li, and B in incorporating water and its low solubility over remarkable variations in the abundances of those elements in most natural samples, quartz is not a major water carrier compared to other nominally anhydrous minerals (NAMs) in the crust. The partitioning of water between quartz and other crustal NAMs such as feldspar, pyroxenes, rutile, and garnet is redox‐influenced, and is unlikely to be constant in the crust.

Effects of Redox State on the Efficient Uptake of Cell Permeable Peptide in Mammalian Cells

We investigated whether a cell-penetrating peptide linked via a disulfide bond to a fluorophore-labeled cargo peptide can be used to interrogate changes in cellular redox state. A fluorescence resonance energy transfer (FRET) pair was constructed so that the cargo peptide was labeled with fluorescein amidite (FAM) and the cell-penetrating peptide was attached to a quencher. Incubation of cells in culture with the FRET construct was visualized using live-cell, time-lapse imaging, which demonstrated earlier cellular uptake of the construct when cells were treated with the reducing agent n-acetylcysteine (NAC). The FRET peptide construct was easily detected in cells cultured in 96-well plates using a plate-reader. Treatment of cells with various classes of reducing or oxidizing agents resulted in an increase or decrease in FAM fluorescence, respectively. Changes in FAM fluorescence correlated significantly with redox-sensitive green fluorescent protein ratios in cells treated with hydrogen peroxide but not NAC. Detection of relative changes in cellular redox state was enhanced by the fact that uptake of the cell-penetrating peptide occurred more quickly in relatively reduced compared with oxidized cells. We conclude that cell-penetrating peptides coupled via disulfide bonds to detectable cargo is a novel and specific approach for assessment of relative changes in cellular thiol redox state.

Comparisons of (±)-Benzo[a]pyrene-trans-7,8-Dihydrodiol Activation by Human Cytochrome P450 and Aldo−Keto Reductase Enzymes: Effect of Redox State and Expression Levels

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants that are metabolically activated to proximate carcinogenic trans-dihydrodiols. PAH trans-dihydrodiols are further activated in humans by cytochrome P450 (P450) 1A1 and 1B1 to yield diol-epoxides or by aldo-keto reductases (AKR) 1A1 and 1C1-1C4 to yield reactive and redox-active o-quinones. Reconstituted in vitro systems were used to compare the steady-state kinetic constants for human P450 (P450 1A1 and 1B1) and AKR (AKR1A1, AKR1C1-1C4) mediated metabolism of (+/-)- trans-7,8-dihydroxy-7,8-dihydrobenzo[ a]pyrene ((+/-)-B[ a]P-7,8-diol) at physiological pH. It was found that P450 isoforms yielded much greater k cat/ K m values than AKR enzymes. Initial rates of (+/-)-B[ a]P-7,8-diol oxidation were measured for AKR1A1, AKR1C2, P450 1A1, and P450 1B1 as the ratio of NADPH/NAD (+) cofactors was varied to determine the redox state necessary for AKRs to successfully compete for trans-dihydrodiols. P450 and AKR enzymes equally competed for (+/-)-B[ a]P-7,8-diol substrate at an NADPH/NAD (+) ratio equal to 0.001. The resting NADPH/NAD (+) ratio was determined in A549 human lung adenocarcinoma cells to be 0.28. These data suggest that the P450 pathway would be favored over the AKR pathway if the enzymes were equally expressed. Basal mRNA transcript levels of AKR1C1-1C3 exceed those of both basal and 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD)-induced P450 1A1 and 1B1 by up to 90-fold in A549 cells as measured by real-time reverse transcriptase polymerase chain reaction (RT-PCR) methods. AKR expression levels were comparable to TCDD-induced P450 1A1 and 1B1 in HBEC-KT immortalized normal human bronchial epithelial cells. Functional assays of both A549 and HBEC-KT cell lysates demonstrated a lack of TCDD-inducible P450 1A1/1B1 activity but robust basal expression of AKR1A1 and AKR1C activities, where the functional assay for P450 detection is 300-fold more sensitive than the functional assay for AKR isoforms. These data suggest that AKR enzymes may effectively compete with P450 1A1/1B1 for PAH trans-dihydrodiol activation in human lung cells.

Sirtuin to Become Astrocytes?

Although neural progenitor cells (NPCs) can differentiate into neurons, astrocytes, or oligodendrocytes, brain injury typically stimulates production of astrocytes in preference to neurons (see Libert et al .). Noting that various neurological diseases are associated with inflammation, which promotes oxidative conditions, Prozorovski et al . investigated the effects of redox state on NPC differentiation. Pharmacological inhibition of antioxidative enzymes (oxidative conditions) decreased proliferation of mouse cortical NPCs cultured in the presence of basic fibroblast growth factor (bFGF), whereas reducing conditions enhanced NPC proliferation. The fraction of cells that differentiated into astrocytes after bFGF withdrawal was greater when NPCs had been cultured under oxidative conditions, whereas the fraction that differentiated into neurons was smaller. In contrast, cells that had been cultured under reducing conditions were more likely to differentiate into neurons and less likely to differentiate into astrocytes. Expression of the histone deacetylase Sirt1 was increased in NPCs cultured under oxidative conditions, and Sirt1 knockdown with siRNA blocked the effects of oxidation on NPC differentiation. Oxidative conditions promoted association of Sirt1 with the transcription factor Hes1 and with the promoter of Mash1 , which encodes a neurogenic transcription factor, and led to decreased acetylation of histone H3, residue Lys9, and a Sirt1-dependent decrease in Mash1 expression. Mouse pups injected with a pro-oxidant showed an increase in Sirt1 immunoreactivity in a germinal region of the brain, along with a decrease in neurogenesis; in utero electroporation with shRNA directed against Sirt1 increased neurogenesis in such oxidant-treated pups. Thus, the authors conclude that nontoxic manipulation of redox conditions can influence NPC fate and that Sirt1 plays a critical role in this process. T. Prozorovski, U. Schulze-Topphoff, R. Glumm, J. Baumgart, F. Schröter, O. Ninnemann, E. Siegert, I. Bendix, O. Brüstle, R. Nitsch, F. Zipp, O. Aktas, Sirt1 contributes critically to the redox-dependent fate of neural progenitors. Nat. Cell Biol. 10 , 385-394 (2008). [PubMed] S. Libert, D. Cohen, L. Guarente, Neurogenesis directed by Sirt1. Nat. Cell Biol. 10 , 373-374 (2008). [PubMed]

Structure-Property Relationships in Industrial and Natural Glasses

The structure and properties of both natural and industrial glasses are influenced by the presence of small amounts of specific elements. Selected examples illustrate the roles of various elements in controlling properties such as coloration, stability, and optical and thermal properties, as well as the effect of redox state of multivalent elements (Ni, Fe, Zn, Zr, Mo) on chemical properties.

The effect of redox state on the local structural environment of iron in silicate glasses: a combined XAFS spectroscopy, molecular dynamics, and bond valence study

A series of 27 silicate glasses of various compositions containing 0.2–2 at.% iron were synthesized at various oxygen fugacity values. The glasses were examined using X-ray absorption fine structure (XANES) spectroscopy at the Fe K-edge in order to determine iron oxidation state and first-neighbor coordination number. Spectral information extracted from the pre-edge region and principal component analysis (PCA) of the XANES region, together with a spectral inversion, were used to derive the end-member spectral components for Fe(II) and Fe(III). Linear trends in the pre-edge features were observed for most compositional series of the glasses examined as a function of Fe(II)/Fe(III) content. These linear trends are believed to be due to the similarity of average coordination numbers for both Fe(II) and Fe(III) end-members in each series. This result is consistent with model simulations of the XANES region and molecular dynamics (MD) simulations for the two end-member compositions which also show that Fe(II) and Fe(III) have similar average coordination numbers. These simulations also suggest the presence of five-coordinated Fe(III) in the melt phase. Based on a bond valence analysis of these MD simulations, a simple model is proposed to help predict the speciation of iron in oxide and silicate glasses and melts.

Mitochondrial Metabolism Sets the Maximal Limit of Fuel-stimulated Insulin Secretion in a Model Pancreatic Beta Cell: A SURVEY OF FOUR FUEL SECRETAGOGUES

The precise metabolic steps that couple glucose catabolism to insulin secretion in the pancreatic beta cell are incompletely understood. ATP generated from glycolytic metabolism in the cytosol, from mitochondrial metabolism, and/or from the hydrogen shuttles operating between cytosolic and mitochondrial compartments has been implicated as an important coupling factor. To identify the importance of each of these metabolic pathways, we have compared the fates of four fuel secretagogues (glucose, pyruvate, dihydroxyacetone, and glycerol) in the INS1-E beta cell line. Two of these fuels, dihydroxyacetone and glycerol, are normally ineffective as secretagogues but are enabled by adenovirus-mediated expression of glycerol kinase. Comparison of these two particular fuels allows the effect of redox state on insulin secretion to be evaluated since the phosphorylated products dihydroxyacetone phosphate and glycerol phosphate lie on opposite sides of the NADH-consuming glycerophosphate dehydrogenase reaction. Based upon measurements of glycolytic metabolites, mitochondrial oxidation, mitochondrial matrix calcium, and mitochondrial membrane potential, we find that insulin secretion most tightly correlates with mitochondrial metabolism for each of the four fuels. In the case of glucose stimulation, the high control strength of glucose phosphorylation sets the pace of glucose metabolism and thus the rate of insulin secretion. However, bypassing this reaction with pyruvate, dihydroxyacetone, or glycerol uncovers constraints imposed by mitochondrial metabolism, each of which attains a similar maximal limit of insulin secretion. More specifically, we found that the hyperpolarization of the mitochondrial membrane, related to the proton export from the mitochondrial matrix, correlates well with insulin secretion. Based on these findings, we propose that fuel-stimulated secretion is in fact limited by the inherent thermodynamic constraints of proton gradient formation.

Effect of redox state on unfolding energetics of heme proteins

Both the enthalpic and entropic contributions to unfolding of three heme proteins, cytochrome b 562, cytochrome c and myoglobin, are larger for the reduced than for the oxidized form. Thus, the higher thermodynamic stability of a reduced, as compared to an oxidized, heme protein is the net result of a large increase of favorable enthalpy and a small increase in unfavorable entropy. Upon comparing the unfolding energetics of the heme proteins to those of other single-domain proteins I find that protein length is the primary determinant of the thermodynamics.

A neutron reflectivity study of [Os(bipy) 2(PVP) 10Cl] + polymer film modified electrodes: effect of redox state and counter ion

The effects of redox state (Os[II] vs. Os[III]) and counter ion (perchlorate vs. p-toluenesulphonate) on the polymer and solvent density distributions in films of electroactive [Os(bipy) 2(PVP) 10Cl] + were determined using neutron reflectivity. The changes in polymer structure upon immersion in solvent and upon redox cycling the film in these electrolytes were also investigated. The as-prepared dry polymer film swelled appreciably upon immersion in aqueous solutions. Using p-toluenesulphonate as the counter ion caused pronounced changes to film structure upon both redox cycling and holding it in a fixed oxidation state; the perchlorate anion was found to be much less disruptive. Surprisingly, the effect on film structure of changing anion was much more pronounced than the effect of changing film redox state, i.e. charge density.

The effect of redox state on the folding free energy of azurin

The unfolding of oxidized and reduced azurin by guanidine hydrochloride has been monitored by circular dichroism. Dilution experiments showed the unfolding to be reversible, and the equilibrium data have been interpreted in terms of a two-state model. The protein is stabilized by the strong metal binding in the native state, so that the folding free energy is as high as –52.2 kJ mol–1 for the oxidized protein. The reduced protein is less stable, with a folding free energy of –40.0 kJ mol–1. A thermodynamic cycle shows, as a consequence, that unfolded azurin has a reduction potential 0.13 V above that of the folded protein. This is explained by the bipyramidal site in the native fold stabilizing Cu(II) by a rack mechanism, with the same geometry being maintained in the Cu(I) form. In the unfolded protein, on the other hand, the coordination geometries are expected to differ for the two oxidation states, Cu(I) being stabilized by the cysteine thiol group in a linear or trigonal symmetry, whereas Cu(II) prefers oxygen ligands in a tetragonal geometry.

Effect of redox state on the response of poly-N-(2-cyanoethyl)pyrrole coated thickness-shear mode acoustic wave sensors to organic vapours

Different redox states of poly-N-(2-cyanoethyl)pyrrole (PCPY) films were prepared by electropolymerization and subsequent oxidation or reduction on the surface of thickness-shear mode (TSM) acoustic wave sensors. The resulting films were characterized by cyclic voltammetry, impedance spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The response of the coated sensors to organic vapours consisting of 9-carbon chains with different functionalities was also studied. The observed responses were dependent on both film redox state and organic vapour properties. All films showed high sensitivity to nona-3,6-dien-1-ol, an aroma component characteristic of early degradation of fresh fish. Principal components analysis allowed all five analytes to be distinguished in the discriminant plane using only different redox state PCPY films.

Significance of iron and cobalt partitioning between plagioclase and biotite for problems concerning the Eu2+/Eu3+ ratio, europium anomaly, and magnetite-/ilmenite-series designation for granitic rocks from the Inner Zone of southwestern Japan

Abundances of REEs and other trace elements were determined for granitic rocks and their mineral separates from the Sanin, Sanyo, and Ryoke belts in the Inner Zone of southwest Japan. Among those data obtained, the Fe and Co partition coefficients between plagioclase and biotite were found to be specially important. The partition coefficients for Fe are negatively correlated with those for Co, and values for the magnetite-series granites from Sanin belt are clearly separated from those for the ilmenite-series granites of Ryoke belt. The Sanyo belt samples, which include both types of granites, fall within the range of the Ryoke ilmenite-series granites. The variation of Fe and Co partition coefficients can be interpreted by the difference in redox states, crystal chemistry of these minerals, and kinetic disequilibrium effect. The Sanyo belt data suggest that the ilmenite-series granites were converted from a magma with magnetite-series affinity during later solidification stages. Moreover, the Eu2+/Eu3+ ratios in minerals were calculated by the Philpotts' method in which the equivalence of Eu2+ and Sr2+ partitioning is assumed. The Eu2+/Eu3+ ratio in plagioclase from the Sanyo and Ryoke belt granites seems to be correlated with the whole-rock Fe2+/Fe3+, though the Sanin belt granites tend to show high plagioclase Eu2+/Eu3+ ratios probably due to a disequilibration caused by rapid solidification. Furthermore, effect of redox states on the size of the Eu anomaly in plagioclase/melt partition coefficient was examined from the plagioclase Eu2+/Eu3+ data of the granites.

Effect of redox state on the dynamics Photosystem II during steady-state photosynthesis in eucaryotic algae

Using a pump and probe-flash technique we simultaneously measured changes in fluorescence yields (ΔΦ) and the yield of oxygen produced by the pump flash ( Y) during steady-state photosynthesis in continuous background light in two species of eucaryotic algae, Chlorella pyrenoidosa, a chlorophyte, and Chaetoceros gracilis, a diatom. By varying the pump-flash intensity, we examined the flash-intensity saturation curves for ΔΦ and Y. When a small fraction of Photosystem (PS) II traps is closed by a blue-green background light the flash-intensity saturation curves for ΔΨ and Y closely followed a cumulative one-hit Poisson function. However, in cells exposed to a far-red background light (more than 720 nm) the flash-intensity saturation curve for ΔΦ (but not Y) rose faster than predicted by a one-hit Poisson model. These results suggest that energy transfer between PS II reaction centers is moderated by the spectral quality of a continuous photon flux. Using saturating pump flashes we calculated the relative fraction of open/closed PS II reaction centers as perceived from the donor and acceptor sides as the background irradiance was changed. The relative changes in ΔΦ and Y were highly correlated at low and moderate levels of continuous background light, regardless of spectral quality. At high continuous photon fluxes, however, Y declined faster with increasing background irradiance than ΔΦ. Based on kinetic data is appears that the uncoupling between Y and ΔΦ at high photon flux densities is largely due to cyclic electron flow around PS II, which is negligible at subsaturating background irradiance levels. Cyclic electron flow around PS II accounted for 15–28% of the linear electron flow and may reduce damage to PS II reaction centers at supraoptimal irradiance levels.

Control of gluconeogenesis in chick ( Gallus domesticus) isolated hepatocytes: Effect of redox state and phosphoenolpyruvate carboxykinase (EC 4.1.1.32) location

1. 1. Hepatocytes isolated from 3- to 5-week old chicks synthesized glucose from a variety of precursors. Laetate and fructose proved the most effective with pyruvate less so and glycerol and alanine relatively poor. 2. 2. Oleate inhibited gluconeogenesis from lactate, pyruvate and glycerol. 3. 3. Ethanol inhibited gluconeogenesis from lactate, glycerol, glyceraldehyde and fructose but stimulated gluconeogenesis from pyruvate. All these effects were abolished by pyrazole. 4. 4. Phosphoenolpyruvate carboxykinase was located almost exclusively within the mitochondria. Quinolinate produced inhibition of gluconeogenesis by hepatocytes at high concentration (20–50 mM) whereas the enzyme was inhibited at much lower concentration (2–4 mM). 5. 5. The aminotransferase inhibitor, aminooxyaeetate, inhibited gluconeogenesis from lactate, glycerol and to a small extent from fructose but not from pyruvate.