SEARCH · PubMed Health

Results for “Redox adaptation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed2003

Role of redox imbalance in the molecular mechanisms responsible for immunosenescence.

The elderly suffer impairments to their immune system, evidenced by higher susceptibility to infections, cancer, and many diseases believed to be autoimmune in nature. A dysregulated overexpression of many proinflammatory cytokines also occurs with aging, as does the synthesis of enzymes that control expression of inflammatory lipid mediators and reactive oxygen species. An inappropriate activation of redox-controlled transcription factors, like nuclear factor-kappaB, occurs in many tissues from aged donors, and has been linked to excesses in cellular oxidative stress. Recently, the peroxisome proliferator-activated receptor-alpha (PPARalpha) has been evaluated for its effects on inflammatory and adaptive immune processes. PPARalpha provides redox-balancing influences on various lymphoid cell types and their inducible responses. We recently discovered that PPARalpha transiently suppresses the transcription of gamma-interferon (IFNgamma) by inhibiting the induction of T-bet. We now report that PPARalpha expression in CD4+ T cells is affected by the aging process. Lower PPARalpha levels are present in aged CD4+ T cells, and appear responsible for the suppressed interleukin-2 and exaggerated IFNgamma responses by these cells. Restoration of PPARalpha, T-bet, interleukin-2, and IFNgamma responses was found in T cells from aged animals supplemented with vitamin E, suggesting that interventions that focus on restoring redox balance might benefit the ailing aged immune system.

Administration, Oral↗

PubMed1980

Binary oscillations in the rate of reoxidation of the primary acceptor of photosystem II.

The decay of fluorescence yield following each of a series of saturating laser flashes has been used to monitor the kinetics of reoxidation of the primary acceptor of Photosystem II under conditions of varied redox potential. 1. In dark-adapted chloroplasts, a damped binary oscillation as a function of flash number was observed in the kinetics of the decay of the fluorescence yield. The decay was faster on odd than on even-numbered flashes. 2. In the presence of low concentrations of 1,4-benzoquinone, the oscillation was more marked, and over the range approx 200--350 mV, independent of redox potential. The decay following flash 1 under these conditions had a half-time of approx. 200--400 microseconds. The decay following flash 2 was decelerated; the initial rate was up to 10-fold slower than after flash 1. 3. We suggest that the kinetics following a single flash reflect the rate of the reaction Q-B leads to QB-, and following the second flash, Q-B- leads to QB2-. Benzoquinone at low concentrations oxidises a residual fraction of B- which is usually reduced in the dark before the flash sequence. 4. A faster component in the decay (t u/2 approximately 140 microseconds) following the first flash titrated in over the range Eh greater than 350 mV. The binary oscillation was still apparent but delayed by one flash. 5. We discuss the relative redox potentials of the couples B/B- and B-/B2-, and the role of the component which titrates in at Eh greater than 350 mV.

Chloroplasts↗

PubMed2007

Thyroid hormone calorigenesis and mitochondrial redox signaling: upregulation of gene expression.

Thyroid hormone (TH, T3) is required for the normal function of most tissues, with major effects on O2 consumption and metabolic rate. These are due to transcriptional activation of respiratory genes through the interaction of T3-liganded TH receptors with TH response elements or the activation of intermediate factors, with the consequent higher rates of mitochondrial oxidative phosphorylation and reactive O2 species (ROS) generation and antioxidant depletion. The genomic effects of TH are accompanied by redox upregulation of the liver expression of cytokines (tumor necrosis factor-alpha [TNF-alpha]), enzymes (manganese superoxide dismutase), and anti-apoptotic proteins (Bcl-2), via a cascade initiated by TNF-alpha produced by Kupffer cells and involving inhibitor of kappa-B phosphorylation and nuclear factor-kappa-B activation. Thus, TH calorigenesis triggers non-genomic effects leading to an expression pattern that may represent an adaptive mechanism to re-establish redox homeostasis and promote cell survival under conditions of ROS toxicity secondary to TH-induced oxidative stress. Mechanisms of expression of respiratory and redox-sensitive genes may be functionally integrated, which could be of importance to understand the complexities of TH action and the outcome of thyroid gland dysfunction.

Animals↗

PubMed2002

Oxygen homeostasis, thiol equilibrium and redox regulation of signalling transcription factors in the alveolar epithelium.

There is growing evidence linking the pathophysiology of lung disease to an imbalance state of reduction-oxidation (redox) equilibrium. The therapeutic potential of glutathione, an ubiquitous sulfhydryl thiol, and its immunopharmacological properties in the airway epithelium bears clinical consequences for the paediatric treatment of respiratory distress (RD). Dynamic variation in alveolar pO(2) and its effect on redox state may impose a direct role in modulating the pattern of gene expression in lung tissues and, accordingly, could be pivotal in determining cellular fate under these conditions. Hypoxia-inducible factor-1alpha (HIF-1alpha) and nuclear factor-kappaB (NF-kappaB) are redox-sensitive transcription factors of particular importance because their differential activation by reducing and oxidizing signals, respectively, regulate the expression/suppression of O(2)-responsive genes. The regulation of these transcription factors, therefore, which is redox sensitive, is consistent with their roles in coordinating adaptive homeostatic responses to oxidative stress. Functionally, the relationship between O(2), glutathione biosynthesis and transcription factor activity bears typical implications for the pattern of cellular survivorship and alveolarization on exposure to O(2)-linked stresses. In this review, I discuss (1) the HIF-1alpha/NF-kappaB responsiveness to dynamic changes in pO(2) characteristic of the transition period from placental to pulmonary-based respiration, (2) the capacity of the alveolar epithelium to engage in glutathione biosynthesis and redox shuttling, effectively forming a feedback mechanism governing gene expression, (3) the restitution of antioxidant/prooxidant equilibrium following oxidative challenge and its dependency on the adaptive coordination of responses between redox-associated signalling pathways controlling apoptosis and genetic regulatory factors and (4) a likely association between oxidative stress and the evolution of an inflammatory signal through the pleiotropic O(2)-sensitive cytokines.

Homeostasis↗

PubMed1995

Oxygen consumption in the rat outer and inner retina: light- and pharmacologically-induced inhibition.

Biochemical, physiological and histological data have established that 55-65% of retinal mitochondria are located in the photoreceptor inner segments and suggested that photoreceptors have at least a two-fold greater oxygen consumption (QO2) than the remaining inner retina. QO2 in isolated whole rat retina (QWR), outer retina (QOR) and inner retina (QIR) was measured during dark and rod-saturating light adaptation. The effects of function-specific chemical agents on QWR, QOR and QIR during dark and light adaptation were determined. In addition, the oxidation-reduction (redox) potential of cytochrome a3 of whole, outer and inner retina was measured during dark and light adaptation. During dark adaptation, the mean QWR was 1.62 mumol O2 (mg dry wt)-1 hr-1 and whole retinal level of reduced cytochrome a3 was 19%. They decreased by 24% and 37% during light adaptation, respectively. To determine QOR and QIR during dark and light adaptation, the outer retina was pharmacologically-isolated from inner retina using L-2-amino-4-phosphonobutyric acid plus kynurenic acid (APB/Kyn). Experiments in the presence or absence of APB/Kyn revealed that: (i) QOR, but not QIR, of the dark-adapted retina was decreased 37% during light adaptation, (ii) the outer and inner retina consumed 65% and 35% of the QWR during dark adaptation, respectively, and 54% and 46% of the QWR during light adaptation, respectively, (iii) the level of reduced retinal cytochrome a3 in the outer, but not inner, retina was decreased 34% during light adaptation, (iv) during light adaptation, the rate of QO2 was equal in the outer and inner retina, and (v) the effects of APB/Kyn were reversible. These results establish that the mean rate of QIR and retinal cytochrome a3 are unchanged during dark or light adaptation. In addition, they suggest that QOR:QIR in the rat may be modeled using a 65%:35% model during DA and a 55%:45% model during LA. All the function-specific agents--IBMX, lead, diltiazem, ouabain, CO2+ plus Mg2+ and verapamil--significantly decreased QWR during dark and light adaptation. A more detailed analysis revealed that IBMX and lead each selectively reduced (> or = 90%) QOR during dark adaptation whereas CO2+ plus Mg2+ and verapamil each selectively reduced (> or = 93%) QIR during dark and light adaptation. These results are consistent with the known pharmacological sites and mechanisms of these agents. Additional experiments determined that the IBMX- and lead-induced inhibition of QOR during dark adaptation resulted, either wholly or partially, from the influx of extracellular Ca2+. During dark adaptation in Ca(2+)-free medium: (i) QWR and QOR increased while QIR was unchanged, (ii) QOR was not decreased in the presence of IBMX and (iii) QOR was only partially decreased in the presence of lead.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Methyl-3-isobutylxanthine↗

PubMed2002

Regulation of Saccharomyces cerevisiae FET4 by oxygen and iron.

Saccharomyces cerevisiae expresses two distinct iron transport systems under aerobic and anaerobic conditions. The high affinity transporters, Ftr1p and Fet3p, are primarily expressed in oxygenated cultures, whereas anaerobic conditions induce the low affinity iron transporter, Fet4p. The oxygen regulation of FET4 was found to involve the Rox1p transcriptional repressor. The physiological significance of this control by Rox1p is twofold. First, FET4 repression by Rox1p under oxygenated conditions helps minimize metal toxicity. Sensitivity towards cadmium was high in either anaerobically grown wild-type yeast or in oxygenated rox1Delta strains, and in both cases cadmium toxicity was reversed by FET4 mutations. Secondly, the loss of Rox1p repression under anaerobic conditions serves to induce FET4 and facilitate continual accumulation of iron. We noted that fet4 mutants accumulate lower levels of iron under anaerobic conditions. Regulation of FET4 was examined using FET4-lacZ reporters. We found that FET4 contains a complex promoter regulated both by oxygen and iron status. The region surrounding approximately -960 to -490 contains two consensus Rox1p binding sites and mediates Rox1p, but not iron control of FET4. Sequences downstream of -490 harbor a consensus binding site for the iron regulatory factor Aft1p that is essential for iron regulation in wild-type strains. In addition, a secondary mode of iron regulation becomes evident in strains lacking AFT1. The induction by iron limitation in conjunction with low oxygen is more than additive, suggesting that these activities are synergistic. Fet4p is not the only metal transporter that is negatively regulated by oxygen; we find that Rox1p also represses S. cerevisiae SMF3, proposed to function in vacuolar iron transport. This oxygen control of iron transporter gene expression is part of an adaptation response to changes in the redox state of transition metals.

Anaerobiosis↗

PubMed2003

Role of PKC-delta activity in glutathione-depleted neuroblastoma cells.

Protein kinases C (PKCs) are a family of isoenzymes sensitive to oxidative modifications and involved in the transduction signal pathways that regulate cell growth. As such, they can act as cellular sensors able to intercept intracellular redox changes and promote the primary adaptive cell response. In this study, we have demonstrated that PKC isoforms are specifically influenced by the amount of intracellular glutathione (GSH). The greatest GSH depletion is associated with a maximal reactive oxygen species (ROS) production and accompanied by an increase in the activity of the delta isoform and a concomitant inactivation of alpha. ROS generation induced early morphological changes in GSH-depleted neuroblastoma cells characterized, at the intracellular level, by the modulation of PKC-delta activity that was involved in the pathway leading to apoptosis. When cells were pretreated with rottlerin, their survival was improved by the ability of this compound to inhibit the activity of PKC-delta and to counteract ROS production. These results define a novel role of PKC-delta in the cell signaling pathway triggered by GSH loss normally associated with many neurodegenerative diseases and clinically employed in the treatment of neuroblastoma.

Acetophenones↗

PubMed2006

Part of the series: from dietary antioxidants to regulators in cellular signalling and gene expression. Role of reactive oxygen species and (phyto)oestrogens in the modulation of adaptive response to stress.

There is increasing evidence that reactive oxygen species (ROS) are not only toxic but play an important role in cellular signalling and in the regulation of gene expression. We, here, discuss two examples of improved adaptive response to an altered cellular redox state. First, differences in longevity between males and females may be explained by a higher expression of antioxidant enzymes in females resulting in a lower yield of mitochondrial ROS. Oestrogens are made responsible for these phenomena. Oestradiol induces glutathione peroxidase-1 and MnSOD by processes requiring the cell surface oestrogen receptor (ER) and the activation of pathways usually involved in oxidative stress response. Second, oxygen radicals produced during moderate exercise as performed during training up-regulate the expression of antioxidant enzymes in muscle cells. An increased level of these enzymes might prevent oxidative damage during exhaustive exercise and should, therefore, not be prevented by antioxidants. The relevance of these findings is discussed in the context with observations made in transgenic animals overexpressing MnSOD or catalase.

Aging↗

PubMed2000

Cell-surface NAD(P)H-oxidase: relationship to trans-plasma membrane NADH-oxidoreductase and a potential source of circulating NADH-oxidase.

The surface of mammalian cells faces an oxidizing environment that has the potential to damage proteins, lipids, and carbohydrates to which it is exposed. In contrast, the cytoplasm is reducing and its redox state is tightly regulated. Trans-plasma membrane oxidoreductases that shift electrons from cytosolic NADH to external electron acceptors such as oxygen are widely involved in cellular redox control. They reduce oxygen to water and may generate reactive oxygen species such as superoxide and hydrogen peroxide. In addition, external NAD(P)H-oxidases have been demonstrated on intact cells and as eluted proteins, but the relationship between trans-plasma membrane NADH-oxidoreductases and cell-surface NAD(P)H-oxidases is not known. To investigate further the relationship between plasma membrane NAD(P)H-oxidoreductases, and to gain insight into the physiological functions of these redox active membrane proteins, we have adapted a simple colorimetric assay for measuring the trans-plasma membrane NADH-oxidoreductase activity of viable cells to measure NAD(P)H-oxidase at the cell surface in real time. Using the cell-impermeable tetrazolium salt WST-1 in the presence of NADH or NADPH, but in the absence of an intermediate electron acceptor, we show that cell-surface NAD(P)H-oxidase is widely expressed on mammalian cells, being more abundant on rapidly proliferating cells than on resting neutrophils and spleen cells. The ratio of cofactor dependence of NAD(P)H-oxidase (NADH:NADPH) varied widely between different cells (0.7-5.2), suggesting a family of cell surface oxidases or that the activity of these enzymes may be modulated in various ways. Comparison of NAD(P)H-oxidase on the surface of viable cells with trans-membrane NADH-oxidoreductase, measured with WST-1 in the presence of 1-methoxy PMS, showed that cell-surface NAD(P)H-oxidase was differentially inhibited by the cell-impermeable thiol-blocking agent pCMBS, but was unaffected or stimulated by other thiol blocking agents. Capsaicin, which inhibits trans-plasma membrane NADH-oxidoreductase activity, stimulated surface NAD(P)H-oxidase. Metabolic inhibitors had little effect on surface NAD(P)H-oxidase activity but inhibited trans-plasma membrane activity. These results do not support the view the surface NAD(P)H-oxidase is a terminal oxidase for trans-plasma membrane NADH-oxidoreductase.

4-Chloromercuribenzenesulfonate↗

PubMed1990

Defining hypoxia: a systems view of VO2, glycolysis, energetics, and intracellular PO2.

The necessity for defining hypoxia as O2-limited energy flux rather than low partial pressure is explored from a systems perspective. Oxidative phosphorylation, the Krebs cycle, glycolysis, substrate supply, and cell energetics interact as subsystems; the set point is a match between ATP demand and aerobic ATP production. To this end the transport subsystem must match the transcapillary and mitochondrial O2 fluxes. High transcapillary O2 flux requires intracellular PO2 in the range 1-10 Torr. In this range the O2 drive on electron transport must be compensated by adaptive changes in the phosphorylation and redox drives. Thus the metabolic subsystem supports diffusive O2 transport by maintaining O2 flux at intracellular partial pressures required for O2 release from blood. Since responses to stress are distributed according to the state of the entire system, several simultaneous metabolic measurements, including intracellular PO2 (or a known direction of change in intracellular PO2) and the O2 dependence of a measurable function are required to judge the adequacy of O2 supply. ATP demand and aerobic capacity must also be evaluated, because the hypoxic threshold depends on the ratio of ATP demand to aerobic capacity. The application and limitation of commonly used criteria of hypoxia are discussed, and a more precise terminology is proposed.

Adenosine Triphosphate↗

PubMed1982

The relationship of biliary glutathione disulfide efflux and intracellular glutathione disulfide content in perfused rat liver.

The intracellular glutathione redox state was estimated using newly adapted methods for tissue analysis. Under standard perfusion conditions of rat liver perfused in situ, intracellular GSH content was 5.5 mumol X g of liver-1, and intracellular GSSG content was 18 nmol X g of liver-1, resulting in a GSH/GSSG ratio of 300. GSSG was transported from the cells into bile. The control rate of release amounts to 0.4 nmol X min-1 X g of liver-1 and corresponds to the rate of release previously observed in anesthetized animals (Sies, H., Koch, O., Martino, E., and Boveris, A. (1979) FEBS Lett. 103, 287-290). No GSSG was released into the caval perfusate. In contrast, GSH release occurs both into bile and into the sinusoidal space, the rates of release being 1 and 14 nmol X min-1 X g of liver-1, respectively. Biliary GSH release in very low in isolated perfused liver. The relationship between intracellular GSSG levels and the rate of biliary GSSG transport was studied. This was achieved in experiments in which internal hydrogen peroxide formation was stimulated with substrates for monoamine oxidase (pargyline-sensitive), or by addition of t-butyl hydroperoxide, or of nitrofurantoin. The apparent concentration ratio, GSSG in bile/GSSG intracellular, was about 50 over the range of intracellular GSSG examined.

Animals↗

PubMed1993

Pneumocystis carinii pneumonia in HIV infected patients: effects of the diseases on glutathione and glutathione disulfide.

Human immunodeficiency virus (HIV) infection is associated with altered levels of glutathione (GSH) in cells and extracellular fluids. GSH is essential for lymphocyte proliferation and inhibits HIV replication. Therefore, determination of GSH and glutathione disulfide (GSSG) levels could be useful as indicators of the progression of the disease. Thyroid hormone levels are altered in acquired immuno-deficiency syndrome (AIDS), such that thyroid hormone might be a useful prognostic indicator of the severity of AIDS. Pneumocystis carinii pneumonia (PCP) is a debilitating disease of the lung that can accompany HIV infection. The effects of pulmonary infections were assessed in AIDS patients on thyroid hormone, GSH, GSSG levels and other parameters. Two groups of AIDS patients were selected, a group with PCP and a control group with other respiratory diseases. GSH was evaluated in plasma, pulmonary lavage fluid, pulmonary biopsy tissue and buccal cells. Levels of GSSG in pulmonary lavage fluid were higher in PCP patients than in controls, which suggests that PCP patients suffer from oxygen radical toxicity in their lungs. PCP patients may have altered plasma GSH utilization such that damaged lung tissue may become less efficient at using plasma GSH. Patients with PCP may have altered CD4 cell functions such that thyroid hormone levels do not correlate with CD4 cell counts. Patients with AIDS and secondary infections of the lung were found to have altered GSH redox states, probably indicative of physiologic adaptation to AIDS.

AIDS-Related Opportunistic Infections↗

PubMed2004

Redox-regulated turnover of Nrf2 is determined by at least two separate protein domains, the redox-sensitive Neh2 degron and the redox-insensitive Neh6 degron.

The Nrf2 transcription factor is more rapidly turned over in cells grown under homeostatic conditions than in those experiencing oxidative stress. The variable turnover of Nrf2 is accomplished through the use of at least two degrons and its redox-sensitive interaction with the Kelch-repeat protein Keap1. In homeostatic COS1 cells, the Neh2 degron confers on Nrf2 a half-life of less than 10 min. Analyses of deletion mutants of a Gal4(HA)mNeh2 fusion protein and full-length mNrf2 indicate that full redox-sensitive Neh2 destabilizing activity depends upon two separate sequences within this N-terminal domain. The DIDLID element (amino acids 17-32) is indispensable for Neh2 activity and appears necessary to recruit a ubiquitin ligase to the fusion protein. A second motif within Neh2, the ETGE tetrapeptide (amino acids 79-82), allows the redox-sensitive recruitment of Nrf2 to Keap1. This interaction, which occurs only in homeostatic cells, enhances the capacity of the Neh2 degron to direct degradation by functioning downstream of ubiquitination mediated by the DIDLID element. By contrast with the situation under homeostatic conditions, the Neh2 degron is neither necessary nor sufficient to account for the characteristic half-life of Nrf2 in oxidatively stressed cells. Instead, the previously uncharacterized, redox-insensitive Neh6 degron (amino acids 329-379) is essential to ensure that the transcription factor is still appropriately turned over in stressed cells, albeit with an increased half-life of 40 min. A model can now be proposed to explain how the turnover of this protein adapts in response to alterations in cellular redox state.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Protein glutathionylation in human central nervous system: potential role in redox regulation of neuronal defense against free radicals.

Neuronal defense against free radicals is mediated primarily by the glutathione system. A cerebral defect of this system gives rise to the oxidative stress occurring in some neurological diseases. Glutathione provides a means of regulating protein function by glutathionylation, consisting of the formation of mixed disulfides between cysteines and glutathione. The glutathionylation of proteins, during both constitutive metabolism and oxidative stress, represents for the cell a mechanism to link physiological processes, and/or adaptive stress responses, to changes in intracellular redox states. In this study, we analyzed the topographic distribution of the protein glutathionylation normally occurring in human central nervous system. Constitutively glutathionylated proteins appeared uniformly distributed throughout all cortical layers of the cerebral and cerebellar cortex as well as throughout the gray matter of the spinal cord. The degree of immunocytochemical staining was clear in neurons, mild in oligodendrocytes, and weaker in astrocytes. The proteins preferentially glutathionylated were cytoskeletal proteins. Our results suggest a potential role of glutathionylation in the redox regulation of neuronal survival and in the control of axon/dendrite stability.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed2006

Comparison of the blood redox status between long-distance and short-distance runners.

Exercise increases the production of reactive oxygen species, which may damage a number of cell constituents. Organisms have developed a sophisticated antioxidant system for protection against reactive oxygen species. Our aim was to compare the adaptive responses of antioxidant mechanisms and the blood redox status of two groups of athletes, long-distance and short-distance runners. Thiobarbituric acid reactive substances, catalase activity and total antioxidant capacity was measured in the serum, while reduced and oxidized glutathione as well as their ratio were determined in blood hemolysates. Serum catalase activity (P<0.001) was found to be three times higher in long-distance compared to short-distance runners (25.4 vs. 8.9 micromol x min(-3) x ml(-1)), whereas the two groups did not differ in the other markers. Catalase activity also correlated significantly with maximal oxygen consumption in long-distance runners. In conclusion, we report here that long-distance and short-distance runners exhibit similar blood redox status judged by several oxidative stress indices, except for the much higher activity of catalase in long-distance runners. This different effect of the two training modules on catalase activity of long-distance runners might be partly due to the high oxygen load imposed during their repeated prolonged exercise bouts.

Adaptation, Physiological↗

PubMedDate not supplied

[Role of oxygen in the vital activity of aerobic organisms].

New experimental data that underlie construction of an adaptive-metabolic conception as to curative effect of hyperbaric oxygenation are systematized in the aspect of evolution. Oxygen under high pressure (300 kPa, 60 min) exerts a specific effect on functions of redox and antiredox systems and nonspecific effect determining adaptation mechanisms of functional (regulatory, effector), metabolic (bioenergy, detoxication, biosynthetic) and morphogenetic (cellular and intracellular regeneration) types at different (hyper-, normo- and hypobiotic) levels of vital activity as dependent on the metabolic activity of the functional structures under pathology conditions.

Adaptation, Physiological↗

PubMed1986

Glutathione redox cycle enzyme activities in erythrocytes of multiple sclerosis patients.

The erythrocytes of multiple sclerosis patients with elevated superoxide dismutase levels were tested for the activities of glutathione redox cycle enzymes. No differences were observed between multiple sclerosis and normal control erythrocytes when the activities were referred to either hemoglobin concentration or lactate dehydrogenase content. Our results indicate that no adaptative changes occur in the activities of glutathione redox cycle enzymes in erythrocytes of multiple sclerosis subjects as a consequence of an elevated superoxide dismutase level.

Adult↗

PubMed2003

Redox potentials of the oriented film of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins.

The redox potentials of the oriented films of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins (bR), prepared by adsorbing purple membrane (PM) sheets or its mutant on a Pt electrode, have been examined. The redox potentials (V) of the wild-type bR were -470 mV for the 13-cis configuration of the retinal Shiff base in bR and -757 mV for the all-trans configuration in H(2)O, and -433 mV for the 13-cis configuration and -742 mV for the all-trans configuration in D(2)O. The solvent isotope effect (DeltaV=V(D(2)O)-V(H(2)O)), which shifts the redox potential to a higher value, originates from the cooperative rearrangements of the extensively hydrogen-bonded water molecules around the protonated C=N part in the retinal Schiff base. The redox potential of bR was much higher for the 13-cis configuration than that for the all-trans configuration. The redox potentials for the E194Q mutant in the extracellular region were -507 mV for the 13-cis configuration and -788 mV for the all-trans configuration; and for the E204Q mutant they were -491 mV for the 13-cis configuration and -769 mV for the all-trans configuration. Replacement of the Glu(194) or Glu(204) residues by Gln weakened the electron withdrawing interaction to the protonated C=N bond in the retinal Schiff base. The E204 residue is less linked with the hydrogen-bonded network of the proton release pathway compared with E194. The redox potentials of the D96N mutant in the cytoplasmic region were -471 mV for the 13-cis configuration and -760 mV for the all-trans configuration which were virtually the same as those of the wild-type bR, indicating that the D to N point mutation of the 96 residue had no influence on the interaction between the D96 residue and the C=N part in the Schiff base under the light-adapted condition. The results suggest that the redox potential of bR is closely correlated to the hydrogen-bonded network spanning from the retinal Schiff base to the extracellular surface of bR in the proton transfer pathway.

Bacteriorhodopsins↗