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PubMed1999

Thiol oxidation and reduction in MHC-restricted antigen processing and presentation.

Major histocompatibility complex (MHC) class I molecules are assembled in the endoplasmic reticulum (ER) as a trimer of the class I heavy chain, beta2 microglobulin (beta2m), and a short peptide. Assembly occurs in a complex with additional noncovalently associated proteins, which include the thiol oxidoreductase, ERp57. This molecule facilitates the formation of the correct disulfide bonds in glycoproteins as they fold in the ER and may play a key role in assembling a stable MHC class I-peptide complex. In the endocytic pathway, reduction of protein disulfide bonds is important for the generation of MHC class II-peptide complexes. This process is catalyzed by a gamma-interferon-inducible thiol reductase (GILT). The possible requirement for catalysis of disulfide bond formation in MHC class I-restricted antigen processing and the known requirement for disulfide bond reduction in MHC class II-restricted antigen processing present interesting examples of the adaptation of cellular "housekeeping" functions to facilitate immune responses.

Animals↗
PubMed1995

Oxidative and reductive pathways of estrogens in hormone responsive and non-responsive human breast cancer cells in vitro.

In order to measure the formation and degradation rates of estradiol by human breast cancer cells, after assessing the biochemical basis of hormone responsiveness and growth response to estrogens, we considered both responsive, estrogen receptor (ER) positive, and non-responsive, ER-negative, breast cancer cell lines, i.e. MCF7, ZR75-1 and MDA-MB231. To this end, we employed a novel "intact cell" approach which allows us, after 24 h incubation, to analyze several enzyme activities in sequence, concurrently with the monitoring of labeled precursor degradation. Our investigations led to the following evidence: (a) the reductive activity of the 17 beta-hydroxysteroid oxoreductase (17 beta-HSOR) appears to be higher than the oxidative only in responsive, ER-rich MCF7 and ZR75-1 cells, as also previously observed by others; (b) this activity is, on the contrary, much lower in MDA-MB231 cells and other unresponsive, ER-poor breast cancer cell lines; (c) conversely, the oxidative activity shows an opposite pattern, being limited in MCF7 and ZR75-1 cells and much higher in MDA-MB231 cells. Overall, a 17 beta-HSOR reductive pathway prevails in both MCF7 and ZR75-1 cells, whilst the oxidative pathway is prevalent in MDA-MB231 cells, leading to a large formation of estrone that is no further metabolized, at least in the experimental conditions used. Our results may provide a likely explanation of previous data on the different estrogen content of breast tumor tissues.

Breast Neoplasms↗
PubMed2003

Electron transfer reactions of redox cofactors in spinach photosystem I reaction center protein in lipid films on electrodes.

Thin film voltammetry was used to obtain direct, reversible, electron transfer between electrodes and spinach Photosystem I reaction center (PS I) in lipid films for the first time. This reaction center (RC) protein retains its native conformation in the films, and AFM showed that film structure rearranges during the first several minutes of rehydration of the film. Two well-defined chemically reversible reduction-oxidation peaks were observed for native PS I in the dimyristoylphosphatidylcholine films, and were assigned to phylloquinone, A(1) (E(m) = -0.54 V) and iron-sulfur clusters, F(A)/F(B) (E(m) = -0.19 V) by comparisons with PS I samples selectively depleted of these cofactors. Observed E(m) values may be influenced by protein-lipid interactions and electrode double-layer effects. Voltammetry was consistent with simple kinetically limited electron transfers, and analysis of reduction-oxidation peak separations gave electrochemical rate constants of 7.2 s(-)(1) for A(1) and 65 s(-)(1) for F(A)/F(B). A catalytic process was observed in which electrons were injected from PS I in films to ferredoxin in solution, mimicking in vivo electron shuttle from the terminal F(A)/F(B) cofactors to soluble ferredoxin during photosynthesis.

Catalysis↗
PubMed1995

Reduction of oxidative tissue injury and endothelial dysfunction by graduated reperfusion after cardioplegic arrest in isolated rat hearts.

The aim of this study was to investigate whether or not a graduated resumption of the perfusion pressure after cardioplegic ischaemic arrest will reduce the impact of oxygen free radicals on myocardium and the cardiovasculature. Langendorff-perfused rat hearts were subjected to cardioplegia and subsequent 40 min of global ischaemia at 25 degrees C. Reperfusion was carried out either abruptly (AR) or gradually (i.e., perfusion pressure stepwise increased from 40 to 75 mmHg within 30 min -GR). GR resulted in a significant improvement of percentage recovery of left ventricular systolic pressure as compared to AR. A marked increase of thiobarbituric acid reactive substances (TBARS) was detected in the effluent during AR, accompanied by an impaired release of the endothelial vasodilator NO and diminished coronary flow rates compared to the baseline values. GR resulted in a significant reduction of TBARS in the effluent and promoted a better recovery of coronary flow as well as endothelial release of NO during the later phase of reperfusion. It is concluded that graduated reperfusion is beneficial in reducing free radical mediated peroxidative tissue injury and endothelial dysfunction upon reoxygenation.

Animals↗
PubMed1962

Evaluation of factors affecting the survival of Escherichia coli in sea water. VI. Cysteine.

The relationship between death of cells of Escherichia coli in artificial sea water and time was established as linear, and statistical tests demonstrated that the most suitable measure of survival was log per cent after 24 hr. Survival of E. coli in water supplemented with cysteine at levels of 0.284 x 10(-6) to 284 x 10(-6)m was increased greatly over that in untreated water. To provide an insight into the mode of action of cysteine, the effect of concentration of various sulfhydryl and disulfide compounds was measured, and the influence of several compounds that lack a functional sulfur group but which are capable of affecting oxidation-reduction potential was determined. Moreover, a number of substances related structurally to cysteine were tested to ascertain their influence on the survival of cells of E. coli in artificial sea water. It appeared that the beneficial effect of cysteine was not due to the sulfhydryl group of the amino acid or to the ability of the compound to influence oxidation-reduction potential. Some sulfhydryl compounds had no favorable effect and, in general, disulfides were more active than the corresponding sulfhydryl compounds. Substances that lack a functional sulfur group but influence oxidation-reduction potential had no significant activity. The beneficial effect of a number of compounds related structurally to cysteine indicates that both an amino and carboxyl group are required for activity. It is suggested that cysteine and other amino acids act to increase survival of cells of E. coli in sea water by a chelation mechanism.

Amino Acids↗
PubMed2004

Oxidation and reduction of pyridine nucleotides in alamethicin-permeabilized plant mitochondria.

The inner mitochondrial membrane is selectively permeable, which limits the transport of solutes and metabolites across the membrane. This constitutes a problem when intramitochondrial enzymes are studied. The channel-forming antibiotic AlaM (alamethicin) was used as a potentially less invasive method to permeabilize mitochondria and study the highly branched electron-transport chain in potato tuber (Solanum tuberosum) and pea leaf (Pisum sativum) mitochondria. We show that AlaM permeabilized the inner membrane of plant mitochondria to NAD(P)H, allowing the quantification of internal NAD(P)H dehydrogenases as well as matrix enzymes in situ. AlaM was found to inhibit the electron-transport chain at the external Ca2+-dependent rotenone-insensitive NADH dehydrogenase and around complexes III and IV. Nevertheless, under optimal conditions, especially complex I-mediated NADH oxidation in AlaM-treated mitochondria was much higher than what has been previously measured by other techniques. Our results also show a difference in substrate specificities for complex I in mitochondria as compared with inside-out submitochondrial particles. AlaM facilitated the passage of cofactors to and from the mitochondrial matrix and allowed the determination of NAD+ requirements of malate oxidation in situ. In summary, we conclude that AlaM provides the best method for quantifying NADH dehydrogenase activities and that AlaM will prove to be an important method to study enzymes under conditions that resemble their native environment not only in plant mitochondria but also in other membrane-enclosed compartments, such as intact cells, chloroplasts and peroxisomes.

Alamethicin↗
PubMed1973

Separate intramolecular pathways for reduction and oxidation of cytochrome c in electron transport chain reactions.

The monoiodotyrosine 74, formyltryptophan 59, mononitrotyrosine 67, and carboxymethylmethionine 80 derivatives of horse cytochrome c are defective in their ability to accept electrons from the succinate-cytochrome c reductase system, while their reactions with purified cytochrome c oxidase are essentially those of the native protein. The 4-nitrobenzo-2-oxa-1,3-diazole derivative of lysine 13 of horse cytochrome c and the bis-phenylglyoxal derivative of arginine 13 of Candida krusei cytochrome c have the opposite properties, in that they are readily reduced by the succinate-cytochrome c reductase (EC 1.3.99.1) system but are defective in their capability of transferring electrons to cytochrome c oxidase (EC 1.9.3.1). We conclude that electrons from mitochondrial cytochrome c reductase are transmitted to ferricytochrome c by a different pathway than electrons from ferrocytochrome c to cytochrome c oxidase. The present results are compatible with the concept that the mechanism of reduction involves an aromatic ring channel comprising residues 74, 59, 67, and 80, leading from the "left back" part of the protein to the heme iron. On the other hand, since residue 13 is immediately above the edge of the heme that is at the "front surface" of the molecule, we suggest that the electron leaves ferrocytochrome c to cytochrome c oxidase by way of the edge of pyrrole ring II or the adjacent surface-located sulfur of cysteinyl residue 17, which is thioether bonded to the heme. On this basis, the sites of electron entry and exit in cytochrome c would appear to be some 110 degrees of arc away from each other along the surface of the protein, explaining several previously observed phenomena.

Animals↗
PubMed2000

The oxidation and reduction reactions of bovine serum amine oxidase. A kinetic study.

The presteady-state and steady-state kinetics of bovine serum amine oxidase (BSAO) were analyzed by stopped-flow transient spectroscopy. A simplified model of the catalytic cycle was found to describe the experimental data and the rate constants of the individual steps were used to calculate Michaelis parameters that agree with the direct determinations. In spite of many studies on selected reactions from the catalytic cycle, this is amongst the first efforts to provide a comprehensive kinetic description of the reactions of BSAO, whose results can be compared with the steady-state parameters. The reoxidation reaction by dioxygen is more complex than previously thought, in agreement with a recent report [Su, Q. & Klinman, J.P. (1998) Biochemistry 37, 12513-12525], and occurs in at least two steps whose rate constants, previously undetermined, have been measured. The reaction of the oxidized enzyme with the amine substrate is poorly determined in this type of experiment, thus irreversible combination with aromatic hydrazine inhibitors was used as a model system, demonstrating that the mechanism and rate constants of their reaction is fully compatible with an accurate description of the catalytic cycle with the physiological substrate. These results constitute a simplified, yet complete and consistent, description of the catalytic cycle and offer an interesting comparison with those obtained on plant amine oxidases; two steps of the catalytic cycle are significantly slower in BSAO than in pea seedling or lentil seedling amine oxidases, namely the reoxidation and the trans-iminative proton abstraction occurring in the enzyme-substrate complex. The former difference is rationalized as being due to the low to zero concentration of the semiquinolamine-radical intermediate, while the latter is less easily interpreted.

Amine Oxidase (Copper-Containing)↗
PubMed1998

Role of amino acids in cochlear degeneration: deprivation of cystine induces death of cochlear hair cells of guinea pigs in vitro.

Redox regulation reportedly plays a role in maintaining cochlear homeostasis. However, little is known about the roles of oxidation-reduction systems in the cochlea. We examined the role of the cystine/cysteine oxidation-reduction system in survival of cochlea hair cells in vitro. The survival of hair cells was evaluated in cochlea specimens following incubation with the medium supplemented with various concentrations of cystine. Dying hair cells were detected by the trypan blue extrusion method. The rates of cell death for both outer and inner hair cells increased significantly with a decrease in the concentration of cystine. In addition, the rate of cell death of IHCs tended to be higher than that of OHCs. These findings suggest that the cystine/cysteine system might be required for maintenance of homeostasis in cochlear hair cells, especially in IHCs.

Animals↗
PubMed1997

Mutations in the CYS4 gene provide evidence for regulation of the yeast vacuolar H+-ATPase by oxidation and reduction in vivo.

The vma41-1 mutant was identified in a genetic screen designed to identify novel genes required for vacuolar H+-ATPase activity in Saccharomyces cerevisiae. The VMA41 gene was cloned and shown to be allelic to the CYS4 gene. The CYS4 gene encodes the first enzyme in cysteine biosynthesis, and in addition to cysteine auxotrophy, cys4 mutants have much lower levels of intracellular glutathione than wild-type cells. cys4 mutants display the pH-dependent growth phenotypes characteristic of vma mutants and are unable to accumulate quinacrine in the vacuole, indicating loss of vacuolar acidification in vivo. The vacuolar proton-translocating ATPases (V-ATPase) is synthesized at normal levels and assembled at the vacuolar membrane in cys4 mutants, but its specific activity is reduced (47% of wild type) and the activity is unstable. Addition of reduced glutathione to the growth medium complements the pH-dependent growth phenotype, partially restores vacuolar acidification, and restores wild type levels of ATPase activity. The CYS4 gene was deleted in a strain in which the catalytic site cysteine residue implicated in oxidative inhibition of the yeast V-ATPase has been mutagenized (Liu, Q., Leng, X.-H., Newman, P., Vasilyeva, E., Kane, P. M., and Forgac, M. (1997) J. Biol. Chem. 272, 11750-11756). This catalytic site point mutation suppresses the effects of the cys4 mutation. The data indicate that the acidification defect of cys4 mutants arises from inactivation of the vacuolar ATPase in the less reducing cytosol resulting from loss of Cys4p activity and provide the first evidence for the modulation of V-ATPase activity by the redox state of the environment in vivo.

Catalysis↗
PubMed2003

Protective effect of ascorbic acid in experimental gastric cancer: reduction of oxidative stress.

AIM: Oxidative stress participates in the cell carcinogenesis by inducing DNA mutations. Our aim was to assess whether ascorbic acid, an antioxidant, could have a role in preventing ROS (Reactive Oxygen Species) generation in experimental gastric carcinoma in a rat model. METHODS: Experimental gastric cancer was induced in twelve Wistar male rats (weighting 250-350 g) by profound duodeno-gastric reflux throught split gastrojenunostomy. The rats were allocated to the following groups: Group I (n=6) was the control; Group II (n=6) which was mantained with daily intake of tape water with Vitamin C (30 mg/Kg). After 6 or 12 months, samples of gastric tumor or non tumor mucosa were taken from the anastomosis of both groups. Oxidative stress was measured by superoxide quantification through lucigenin-amplified chemiluminescence base and by staining with Nitrobluetetrazolium. The histopathologic confirmation of adenocarcinoma was made by eosin-hemathoxilin method. RESULTS: The intestinal type of gastric adenocarcinoma was microscopically identified in all animals of group I whereas only 3 rats of group II showed an adenocarcinoma without macroscopic evidence of them. The cancers were located in the anastomosis in all cases. Basal luminescence from tumor gastric tissue generated 38.4+/-6.8 count per minute/mg/X10(6) (mean+/-SD) and 14.9+/-4.0 count per minute/mg/X10(6), respectively, in group I and II animals (P<0.05). The Nitrobluetetrazolium method showed intense staining in tumor tissues but not in non neoplasic mucosa. CONCLUSION: Experimental gastric tumors seem to produce more reactive oxygen species than non neoplasic gastric tissue. The reduction of oxidative stress and gastric tumor incidence in rats were induced by the intake of ascorbic acid. Therefore, it may have a role in the prevention of gastric carcinoma.

Animals↗
PubMed2006

Reduction in oxidative stress by superoxide dismutase overexpression attenuates acute brain injury after subarachnoid hemorrhage via activation of Akt/glycogen synthase kinase-3beta survival signaling.

Recent studies have revealed that oxidative stress has detrimental effects in several models of neurodegenerative diseases, including subarachnoid hemorrhage (SAH). However, how oxidative stress affects acute brain injury after SAH remains unknown. We have previously reported that overexpression of copper/zinc-superoxide dismutase (SOD1) reduces oxidative stress and subsequent neuronal injury after cerebral ischemia. In this study, we investigated the relationship between oxidative stress and acute brain injury after SAH using SOD1 transgenic (Tg) rats. SAH was produced by endovascular perforation in wild-type (Wt) and SOD1 Tg rats. Apoptotic cell death at 24 h, detected by a cell death assay, was significantly decreased in the cerebral cortex of the SOD1 Tg rats compared with the Wt rats. The mortality rate at 24 h was also significantly decreased in the SOD1 Tg rats. A hydroethidine study demonstrated that superoxide anion production after SAH was reduced in the cerebral cortex of the SOD1 Tg rats. Moreover, phosphorylation of Akt and glycogen synthase kinase-3beta (GSK3beta), which are survival signals in apoptotic cell death, was more enhanced in the cerebral cortex of the SOD1 Tg rats after SAH using Western blot analysis and immunohistochemistry. We conclude that reduction in oxidative stress by SOD1 overexpression may attenuate acute brain injury after SAH via activation of Akt/GSK3beta survival signaling.

Animals↗
PubMed1975

Enzymatic oxidation and reduction of C19-delta5-3beta-hydroxysteroids by hepatic microsomes. IV. Induction of DHA hydroxylases and aminopyrine N-demethylase in immature male rats by androgens.

The capacities of various C19 steroids for prematurely inducing the normal metabolic patterns of rat liver in adulthood (70 days old) have been studied with hepatic microsomes of 42-day-old males castrated on day 24, 30, 32, or 34 of life. Dehydroepiandrosterone 16alpha-hydroxylase activity was significantly reduced (P less than 0.05) by castration during this 10-day interval but the 7alpha- and 7beta-hydroxylases, the N-demethylation of aminopyrine, and cytochrome P-450 concentration were unaffected. Daily administration of testosterone stimulated the DHA 16-alpha- and 17beta-hydroxylases, aminopyrine N-demethylation, and increased the P-450 content, but suppressed the 7alpha-hydroxylase. These effects only appeared with more than 1 week of the continuous treatment. Testosterone was the most active of the androgens studied; dihydrotestosterone (DHT) increased the DHA 16alpha-hydroxylase to a lesser extent, but this steroid and etiocholanolone stimulated DHA 7alpha-hydroxylation; androsterone was totally ineffective. These data suggest that testosterone rather than DHT from pubertal testes plays a significant role in control of hepatic oxidative enzyme activities during puberty.

Age Factors↗
PubMed1967

Effects of light and temperature on the monoterpenes of peppermint.

Peppermint (Mentha piperita L.) was grown in a growth chamber under several combinations of temperature and illumination, and the monoterpenes of each leaf pair were analyzed by gas chromatography. Effects on the monoterpenes could be seen in the new leaves after a few days in the growth chamber. Long-day conditions enhanced growth, with a corresponding increase in the total amount of monoterpenes. Either short nights or cool nights, combined with full light intensity during the day, enhanced the formation of menthone and depressed the accumulation of menthofuran and pulegone. Experiments with interrupted night and with low light intensity indicated that photoperiod, as such, does not directly influence the terpene composition. It is suggested that the oxidation-reduction level of the monoterpenes reflects the oxidation-reduction state of the respiratory coenzymes of the terpene-producing cells, and that this, in turn, depends on the concentrations of respiratory substrates in the cells. This suggestion is based on the likelihood that warm nights cause depletion of respiratory substrates, resulting in oxidizing conditions, while cool nights preserve high levels of respiratory substrates, and thus maintain reducing conditions.

Journal Article↗
PubMed2005

NosX function connects to nitrous oxide (N2O) reduction by affecting the Cu(Z) center of NosZ and its activity in vivo.

The effect of loss of the 34-kDa periplasmic NosX protein on the properties of N2O reductase was investigated with an N2O-respiration negative, double mutant of the paralogous genes nosX and nirX of Paracoccus denitrificans. In spite of absence of whole-cell N2O-reducing activity, the purified reductase was catalytically active, which attributes NosX a physiological role in sustaining the reaction cycle. N2O reductase exhibited the spectroscopic features of Cu(A) and the redox-inert, paramagnetic state, Cu(Z)*, of the catalytic center. Cu(Z)*, hitherto considered the result of spontaneous reaction of the reductase with dioxygen, attains cellular significance.

Bacterial Proteins↗
PubMed1989

Chemically induced Parkinson's disease. II: Intermediates in the oxidation and reduction reactions of the 1-methyl-4-phenyl-2,3-dihydropyridinium ion and its deprotonated form.

The one-electron reduction product of 1-methyl-4-phenyl-2,3-dihydropyridinium ion has been generated by pulse radiolysis and its absorption spectrum recorded. This radical was found to decay by second-order kinetics (2k = 9.5 x 10(8) M-1 s-1) to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 1-methyl-4-phenyl-2,3-dihydropyridinium ion. Reactions of the above radical species and that formed by one-electron reduction of 1-methyl-4-phenylpyridinium ion, which can also be generated by one-electron oxidation of 1-methyl-4-phenyl-1,2-dihydropyridine, with a number of molecules of biochemical interest have been studied. The one-electron reduction product of oxidised nicotinamide adenine dinucleotide efficiently reduced 1-methyl-4-phenyl-2,3-dihydropyridinium ion (k = 2.2 x 10(9) M-1 s-1). The relevance of these results in relation to redox cycling, a possible mechanism for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity, is discussed.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1995

Oxidation and reduction of cytochrome c by mitochondrial enzymes of Setaria cervi.

A mitochondria-rich fraction isolated from the cuticle-hypodermis-muscle system of Setaria cervi, a bovine filarial parasite, possessed substrate-coupled cytochrome c reductases and cytochrome c oxidase in appreciable activities. All these activities were located predominantly in the membranes. NADH-coupled cytochrome c reductase was more prominent than NADPH- and succinate-coupled reductases. All the three reductases exhibited marked sensitivity to rotenone and antimycin A. Salicylhydroxamic acid strongly inhibited succinate requiring reductase and cytochrome c oxidase, but the other two reductases only mildly. Sodium azide activated the reductases but substantially inhibited the oxidase activity. Potassium cyanide activated the succinate requiring reductase but did not cause any noticeable change in the activities of pyridine nucleotide linked reductases. Anthelmintics also influenced these activities but no definite correlation could be drawn regarding their mode of action.

Animals↗