MACROION INTERACTIONS INVOLVING COMPONENTS OF THE CYTOCHROME SYSTEM. IV. POLYION-INDUCED REVERSIBLE OXIDATIONS AND REDUCTIONS OF CYTOCHROME C.
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Aspartic Acid↗
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Oxidation and reduction of 4-hydroxyalkenals catalyzed by isozymes of human alcohol dehydrogenase.
4-Hydroxyalkenals, natural cytotoxic products of lipid peroxidation, are substrates for human alcohol dehydrogenases (ADH). Class I and II ADHs reduce aliphatic 4-hydroxyalkenals with chain lengths of from 5 to 15 carbons at pH 7 with kcat and Km values comparable to simple aliphatic aldehydes of the same chain length. Class II is particularly effective in the reduction with kcat values as high as 3300 min-1 for 4-hydroxyundecenal. Class III ADH is essentially inactive toward all of these substrates. The class I and II isozymes also catalyze the oxidation of the 4-hydroxy group at pH 10. However, during the reaction, an NAD(+)-dependent irreversible partial inactivation of the alpha beta 1 isozyme is observed which is attributed, with the aid of computer graphics modeling, to selective modification of the alpha subunit. Both ethanol and 1,10-phenanthroline, known to compete with conventional substrates, instantaneously, reversibly, and competitively inhibit 4-hydroxyalkenal reduction and oxidation, indicating that 4-hydroxyalkenals bind at the same site as do conventional substates. The fact that the class II enzyme pi pi-ADH so far is found only in the liver and that the 4-hydroxyalkenals are the best substrates known for this isozyme suggest that it may play a significant role in cellular defenses in the conversion of the cytotoxic aldehydes to the less reactive alcohols.
Alcohol Dehydrogenase↗
Proton stoichiometry in the reduction of the FAD and disulfide of Escherichia coli thioredoxin reductase. Evidence for a base at the active site.
The oxidation-reduction midpoint potentials, Em, of the FAD and active site disulfide couples of Escherichia coli thioredoxin reductase have been determined from pH 5.5 to 8.5. The FAD and disulfide couples have similar Em values and thus a linked equilibrium of four microscopic enzyme oxidation-reduction states exists. The binding of phenylmercuric acetate to one enzyme form could be monitored which allowed solving the four microscopic Em values. The Em values at pH 7.0 and 12 degrees C of the four couples of thioredoxin reductase are: (S)2-enzyme-FAD/FADH2 = -0.243 V, (SH)2-enzyme-FAD/FADH2 = -0.260 V, (FAD)-enzyme-(S)2/(SH)2 = -0.254 V, and (FADH2)-enzyme-(S)2/(SH)2 = -0.271 V. Thus, at pH 7.0, the FAD and disulfide moieties have a 0.017-V negative interaction and Em values which are different by 0.011 V. The delta Em/delta pH of the FAD couples E2m and E3m are about 0.060 V/pH throughout the pH range studied, showing an approximately 2-proton stoichiometry of reduction of the enzyme FAD. The delta Em/delta pH of the disulfide couples E1m and E4m are about 0.052 V/pH from pH 5.5 to 8.5, showing an apparently nonintegral proton stoichiometry of reduction of 1.8 in this pH range. This proton stoichiometry suggests the presence of a base with an ionization behavior that is linked to the oxidation-reduction state of the disulfide. A novel method is presented for determining the pK values on oxidized and reduced enzyme which agrees with the less accurate classical method. The proton stoichiometry results are consistent with the presence of a thiol-base ion pair in which the pK of the base is elevated from 7.6 in disulfide containing enzyme to greater than 8.5 upon forming an ion pair with a thiol anion of pK 7.0 generated upon reduction of the disulfide. The fluorescence of the FAD in thioredoxin reductase decreases as the pH is lowered with a pK of 7.0, direct evidence for a base near the FAD probably distinct from the base interacting with the dithiol.
Binding Sites↗
Metabolism of geraniol in grape berry mesocarp of Vitis vinifera L. cv. Scheurebe: demonstration of stereoselective reduction, E/Z-isomerization, oxidation and glycosylation.
The metabolism of deuterium labeled geraniol in grape mesocarp of Vitis vinifera L. cv. Scheurebe was studied by in vivo-feeding experiments. Stereoselective reduction to (S)-citronellol, E/Z-isomerization to nerol, oxidation to neral/geranial and glycosylation of the corresponding monoterpene alcohols could be demonstrated. Time course studies including the determination of conversion rates revealed that the activity of these secondary transformations of monoterpenes is dependent on the ripening stage and can be distinguished from the development of the primary monoterpene synthase activities by the sharp increase at the end of the ripening period. The stereoselective biosynthesis of the potent odorant cis-(2S,4R)-rose oxide from labeled geraniol in grape berry mesocarp is demonstrated as well. Since (S)-citronellol is the precursor of cis-(2S,4R)-rose oxide it can be concluded that especially the last part of the ripening period is important for the generation of this potent odorant. This finding confirms the conclusion that a higher concentration of flavor compounds could be established in the berries by leaving the fruit on the vine for extended periods.
Acyclic Monoterpenes↗
Reduction and release of ferritin iron by plant phenolics.
The reductive release of ferritin iron by several naturally occurring o-diphenols was studied. The initial rate of iron release was quantified by spectrophotometric measurement of the Fe(ferrozine)3(2+) complex, which absorbs maximally at 562 nm. The initial rate of iron release was dependent upon o-diphenol concentration, but not on the concentration of the chromophoric chelating agent, ferrozine, Stoichiometric measurements resulted in a ratio of 2Fe(II) released per molecule of o-diphenol. The series of o-diphenols studied included, caffeic acid, chlorogenic acid, dihydrocaffeic acid, 3,4-dihydroxybenzoic acid, and several analogs. These reductants represent an oxidation reduction potential range of 0.38 volts. A direct correlation between reducing power of the o-diphenols and rate of ferritin iron release was observed. Superoxide dismutase, catalase, mannitol, or general radical traps had no effect on the rate of iron removal; however, EDTA and oxalate inhibited iron release. A mechanism for ferritin iron reduction and release by o-diphenols consistent with the experimental observations is discussed.
Animals↗
DIHYDROSTREPTOMYCIN, VITAMIN K2-COUPLED TETRAZOLIUM REDUCTION, AND OXIDATIVE PHOSPHORYLATION IN ESCHERICHIA COLI.
Bragg, P. D. (University of British Columbia, Vancouver, B.C., Canada). Dihydrostreptomycin, vitamin K(2)-coupled tetrazolium reduction, and oxidative phosphorylation in Escherichia coli. J. Bacteriol. 88:1019-1023. 1964.-Dihydrostreptomycin inhibited the vitamin K(2)-coupled pyruvate-triphenyltetrazolium (TTC) reductase system in extracts from antibiotic-sensitive cells, but stimulated this reaction with extracts from a dependent mutant. The effects of nucleotides, phosphate, and uncoupling agents on the vitamin K(2)-TTC system are consistent with the linkage of reduction of the dye through intermediates of oxidative phosphorylation.
Anti-Bacterial Agents↗
Rapid reaction studies on the reduction and oxidation of chicken liver xanthine dehydrogenase by the xanthine/urate and NAD/NADH couples.
Chicken liver xanthine dehydrogenase can be partially reduced by either xanthine or NADH. Reduction to approximately the 2-electron-reduced level occurs with NADH, and reduction beyond the 2-electron level occurs with xanthine. In both cases, the reaction is triphasic. The first and third phases are dependent on reductant concentration, whereas the second phase is not. Oxidation of fully (6-electron) reduced xanthine dehydrogenase by either urate or NAD is monophasic and dependent on the oxidant concentration. Oxidation stops at about the same level of reduction that was reached by the corresponding reductant. The position of this end point is sensitive to the potential of the reactants but is relatively insensitive to excess concentrations of oxidant or reductant. NADH binding to 2-electron-reduced enzyme is implicated in fixing the end point position in those reactions involving pyridine nucleotides, whereas urate binding is involved in fixing the end point of those reactions involving xanthine and urate.
Animals↗
Asymmetric reduction and oxidation of aromatic ketones and alcohols using W110A secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus.
An enantioselective asymmetric reduction of phenyl ring-containing prochiral ketones to yield the corresponding optically active secondary alcohols was achieved with W110A secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus (W110A TESADH) in Tris buffer using 2-propanol (30%, v/v) as cosolvent and cosubstrate. This concentration of 2-propanol was crucial not only to enhance the solubility of hydrophobic phenyl ring-containing substrates in the aqueous reaction medium, but also to shift the equilibrium in the reduction direction. The resulting alcohols have S-configuration, in agreement with Prelog's rule, in which the nicotinamide-adenine dinucleotide phosphate (NADPH) cofactor transfers its pro-R hydride to the re face of the ketone. A series of phenyl ring-containing ketones, such as 4-phenyl-2-butanone (1a) and 1-phenyl-1,3-butadione (2a), were reduced with good to excellent yields and high enantioselectivities. On the other hand, 1-phenyl-2-propanone (7a) was reduced with lower ee than 2-butanone derivatives. (R)-Alcohols, the anti-Prelog products, were obtained by enantiospecific oxidation of (S)-alcohols through oxidative kinetic resolution of the rac-alcohols using W110A TESADH in Tris buffer/acetone (90:10, v/v).
Alcohol Dehydrogenase↗
Ammonia formation in isolated rat liver mitochondria.
Studies of isolated rat liver mitochondria were undertaken in order to evaluate the importance of glutamate transport, oxidation reduction state, and product inhibition on the rates of formation of ammonia from glutamate. Uptake and efflux of glutamate across the mitochondrial membrane were measured isotopically in the presence of rotenone. Efflux was stimulated by H+ in the mitochondrial matrix and was found to be first order with respect to matrix glutamate except when the matrix pH was unphysiologically low. The data suggest that the Km of matrix glutamate for efflux is decreased by H+. Matrix H+ also appeared to stimulate glutamate uptake, but the effect was to increase both the Km of medium glutamates and Vmax. Mitochondria were incubated at 15 and 28 degrees C with glutamate and malonate. Under these conditions, glutamate was metabolized only by the deamination pathway. Flux was evaluated by assay of ammonia formation. Oxidation reduction state was varied with ADP and uncoupling agents. Matrix alpha-ketoglutarate was varied either by the omission of malonate from the incubation media or by adding alpha-ketoglutarate to the external media. Influx and efflux of glutamate could be calculated from previously determined transport parameters. The difference between calculated influx and efflux was found to be equal to ammonia formation under all conditions. It was, therefore, possible to evaluate the relative contributions of oxidation reduction state, transport, and product inhibition as effectors of ammonia formation. The contribution of transport was relatively small while oxidation reduction state exerted a large influence. alpha-Ketoglutarate was found to be a potent competitive inhibitor of ammonia production and glutamate dehydrogenase. Inhibition of glutamate dehydrogenase by alpha-ketoglutarate was judged to be a potentially important modulator of metabolic fluxes.
Ammonia↗
Quinone-enhanced ascorbate reduction of nitric oxide: role of quinone redox potential.
The quinones 1,4-naphthoquinone (NQ), methyl-1,4-naphthoquinone (MNQ), trimethyl-1,4-benzoquinone (TMQ) and 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ-0) enhance the rate of nitric oxide (NO) reduction by ascorbate in nitrogen-saturated phosphate buffer (pH 7.4). The observed rate constants for this reaction were determined to be 16+/-2,215+/-6,290+/-14 and 462+/-18 M-1 s-1, for MNQ, TMQ, NQ and UQ-0, respectively. These rate constants increase with an increase in quinone one-electron redox potential at neutral pH, E1(7). Since NO production is enhanced under hypoxia and under certain pathological conditions, the observations obtained in this work are very relevant to such conditions.
Ascorbic Acid↗
[A relationship between insulin resistance and reduction in oxidative stress in vivo by atorvastatin].
OBJECTIVES: To examine the relationship between insulin resistance (IR) and the reduction of oxidative stress in vivo by the statin atorvastatin. METHODS: This study included 40 patients with hypercholesterolemia without a history of diabetes mellitus (21 males, 19 females, mean age 62 +/- 11 years). Homeostasis assessment insulin resistance (HOMA-IR) was used as a marker for insulin resistance. The patients were divided into two groups [IR group (n = 24) and non-IR group (n = 16), using the cut off level of 1.73]. Urinary 8-iso-prostaglandin F2alpha (U-8-iso) excretion was used as an oxidative stress marker. The subjects were treated with atorvastatin (10 mg/day) for 12 weeks. RESULTS: The IR group had significantly higher U-8-iso levels than the non-IR group before atorvastatin administration (211 +/- 112 vs 137 +/- 33 pg/mg Cr, p = 0.01). Low-density lipoprotein cholesterol, triglyceride, and 8-iso levels were significantly reduced in both groups after 12 weeks, U-8-iso levels were significantly higher in the IR group than the non-IR group (178 +/- 61 vs 110 +/- 38 pg/mg Cr, p = 0.003), and HOMA-IR showed no significant change. Multiple regression analysis after 12 weeks showed that HOMA-IR and triglyceride levels were independent variables for U-8-iso levels (standard regression coefficient = 0.60, 0.59, p < 0.0001, p = 0.0002). CONCLUSIONS: Insulin resistance is important in the occurrence of oxidative stress in patients with hypercholesterolemia. Since atorvastatin does not reduce insulin resistance, further therapy to reduce insulin resistance is necessary for early prevention of cardiovascular events during atorvastatin treatment.
Aged↗
Modulation of the mitochondrial permeability transition pore by pyridine nucleotides and dithiol oxidation at two separate sites.
After accumulation of a Ca2+ load, the addition of uncoupler to respiring rat liver mitochondria is followed by opening of the permeability transition pore (MTP), a voltage-dependent channel sensitive to cyclosporin A. The channel's voltage threshold is profoundly affected under conditions of oxidative stress, with a shift to more negative values that may cause MTP opening at physiological membrane potentials. In this paper we further clarify the mechanisms by which oxidative agents affect the apparent voltage dependence of the MTP. We show that two sites can be experimentally distinguished. (i) A first site is in apparent oxidation-reduction equilibrium with the pyridine nucleotide (PN) pool (NADH/NAD + NADPH/NADP); PN oxidation is matched by increased MTP open probability under conditions where the glutathione pool is kept in the fully reduced state; this site can be blocked by N-ethylmaleimide but not by monobromobimane, a thiol-selective reagent. (ii) A second site coincides with the oxidation-reduction-sensitive dithiol we have recently identified (Petronilli, V., Costantini, P., Scorrano, L., Colonna, R., Passamonti, S., and Bernardi, P. (1994) J. Biol. Chem. 269, 16638-16642); dithiol cross-linking at this site by arsenite or phenylarsine oxide is matched by increased MTP open probability under conditions where the PN pool is kept in the fully reduced state; at variance from the first, this site can be blocked by both N-ethylmaleimide and monobromobimane and is probably in equilibrium with the glutathione pool. Based on these findings, we reassess the mechanisms by which many oxidative agents affect the MTP and resolve conflicting reports on the relative role of PN and glutathione oxidation in the permeability transition within the framework of MTP (dys)regulation at two separate sites.
3-Hydroxybutyric Acid↗
[Reduction of carotenoid oxides with lithium alanate].
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Aluminum↗
Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface.
The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.
Journal Article↗
Molecular biology of nitric oxide synthases. Reduction of complications of cardiopulmonary bypass from platelets and neutrophils by nitric oxide generation from L-arginine and nitric oxide donors.
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Animals↗
Studies in the chemotherapy of tuberculosis: Part VII. The oxidation and reduction products of thiosemicarbazones.
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Oxidation-Reduction↗
Effects of oxidation and reduction on the binding of transcription factors to cis-regulatory elements located in the FGF-4 gene.
Previous studies have shown that the addition of reducing agents to the culture medium of embryonic cell lines stimulates their growth. Moreover, recent studies have shown that the redox state of several transcription factors affects their binding to DNA. In light of these findings, we employed gel mobility shift analysis to examine the effects of oxidation and reduction on the ability of transcription factors to bind cis-regulatory elements located in the FGF-4 gene, which is expressed during early mammalian development. In this study, we demonstrate that both the oxidizing agent diamide and the alkylating agent N-ethylmaleimide inhibit the ability of Oct-1, Oct-3, Sp1, and several Sp1-related nuclear proteins to bind important cis-regulatory elements located in the FGF-4 gene. We also demonstrate that not all transcription factors are affected by oxidation. Specifically, we show that the binding of the transcription factor NF-YA, which binds to a critical CCAAT box, and the binding of a high mobility group (HMG) protein(s), which binds to a critical HMG motif, are not affected by diamide or N-ethylmaleimide. Taken together, our findings and those of others support the hypothesis that the redox state of the cell can regulate gene transcription and, thus, can influence important physiological processes.
Alkylating Agents↗
Catalysis of the oxidation and reduction reactions of steroid and stilbene estrogens by nuclear enzymes.
We demonstrated for the first time that nuclei were able to convert a stilbene estrogen (diethylstilbestrol) to reactive metabolites, which covalently bind to nuclear proteins and DNA. Depending on the cofactor used, nuclear enzymes catalyzed oxidation and/or reduction of stilbene and steroid estrogens. 2-Hydroxyestradiol (a major metabolite of steroidal estrogen, 17 beta-estradiol) and diethylstilbestrol (DES) were oxidized to 2,3-estradiol quinone and DES quinone, respectively, by peroxide-supported nuclear cytochromes P450. A Lineweaver-Burk plot of rate of formation of DES quinone at various substrate concentrations yielded a Km = 15 microM and Vmax = 10 nmol/mg protein/min. The oxidation of DES to DES quinone by nuclei was drastically decreased by known inhibitors of cytochromes P450. DES quinone was reduced back to DES by nuclei in the presence of NADPH, presumably through cytochrome P450 reductase. The reduction of DES quinone to DES by nuclei was significantly inhibited by antibodies and inhibitors of cytochrome P450 reductase. Under reaction conditions similar to oxidation of DES to DES quinone by nuclei, it was observed that nuclear metabolic products of DES were able to covalently bind to nuclear proteins and DNA. The data reported here establish that DES and a catechol estrogen can be oxidized to quinones and that the quinones may be reduced back to the hydroquinones by nuclear preparations when fortified with an appropriate cofactor and that reactive intermediates are involved based on observed covalent binding to macromolecules. The significance of these events, and their possible role in toxicity/cancer/teratogenicity, however, is not at all clear.
Animals↗