Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Dithionite”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 19 recordsLinked to original sources
PubMed2001

Abiotic transformation of perchloroethylene in homogeneous dithionite solution and in suspensions of dithionite-treated clay minerals.

The reductive dechlorination of perchloroethylene (PCE) in homogeneous solutions of dithionite and at the surfaces of dithionite-citrate-bicarbonate (DCB) treated ferruginous smectite and Na-montmorillonite was studied. Transformation products of PCE identified in dosed dithionite-treated samples included TCE, DCE, 1,1,2-trichloroethane (TCA), 1,1-dichloroethane (DCA), chloroacetylene, acetylene, ethene, and ethane. The decomposition of dithionite to sulfate yielded both protons and electrons necessary for hydrodechlorination (hydrogenolysis) of PCE. Dithionite treatment of the Fe-poor Na-montmorillonite enhanced reductive dechlorination of PCE relative to dithionite-treated Fe-rich ferruginous smectite, within the range of 11.5-137.8 mM dithionite. For the same dithionite concentration, the kinetics of the heterogeneous reactions of PCE was generally faster than that of the homogeneous reaction, and higher concentrations of TCE were measured in the heterogeneous reactions. Interestingly, increases in the mass of the clay minerals used, the Fe2+ content in the clay mineral structure, or the dithionite concentration used did not necessarily enhance the abiotic transformation of PCE, as would otherwise be predicted. The most efficient reductive dechlorination of PCE was observed with 0.5% clay (m/v) treated with 34.5 mM dithionite buffered at pH 8.5. The solid-state transfer of electrons to surfaces and edges, rather than the redox capacity, limited the dechlorination of PCE by reduced ferruginous smectite and/or suspensions containing a higher clay mass. The greater reactivity of dithionite-reduced montmorillonite than similarly treated ferruginous smectite is attributed to (i) the well-documented layer collapse and aggregation of chemically reduced clays that increases with the clay's iron content, (ii) the location of solid-phase Fe2+ in the reduced clay mineral and whether it is accessible or inaccessible for reaction with PCE at the mineral edges and surfaces where the reactions are thought to occur, and (iii) the greater swellability of montmorillonite versus ferruginous smectite. The faster dechlorination rate of PCE observed with dithionite-reduced Fe-poor montmorillonite than similarly reduced iron-rich ferruginous smectite suggests that the use of dithionite barriers for in-situ treatment of chlorinated solvent plumes should not be limited to aquifers with Fe-rich sediments.

Aluminum Silicates↗
PubMed1995

Dithionite increases radical formation and decreases vasoconstriction in the lung. Evidence that dithionite does not mimic alveolar hypoxia.

Dithionite is a powerful reducing agent used to deoxygenate hemoglobin and create anaerobic conditions in vitro. Recently, dithionite has been used as a convenient means of creating "hypoxia" in experiments studying the O2 sensor in the pulmonary circulation and carotid body. We evaluated the hypothesis that hypoxia created by hypoxic ventilation and that created by dithionite have different effects on the pulmonary circulation. In vitro, dithionite (10(-5) to 10(-3) mol/L), added to oxygenated Krebs' solution, rapidly created superoxide anion in a dose-dependent manner. Dithionite consumed O2 in parallel with the generation of superoxide radical, with both processes peaking within seconds. Anoxia was sustained only if resupply of O2 was prevented. In isolated rat lungs (whether perfused with autologous blood or Krebs' solution), hypoxic ventilation alone lowered perfusate PO2 from approximately 140 to 40 mm Hg and decreased lung levels of activated oxygen species (AOS), measured by luminol-enhanced chemiluminescence, before the onset of hypoxic pulmonary vasoconstriction. Constrictor responses to angiotensin II and KCl were not impaired by intermittent hypoxic challenges, and lung weight did not increase. In contrast, dithionite impaired constrictor responses of the Krebs' solution-perfused lungs to all vasoconstrictors tested and increased lung weight. When given as a bolus (5 x 10(-3) mol/L) into the pulmonary artery during normoxic ventilation, dithionite caused no vasoconstriction and only briefly lowered PO2 (because of constant resupply of O2 from the alveoli). When superimposed on hypoxic ventilation, dithionite further lowered PO2 from approximately 40 to approximately 0 mm Hg and caused additional constriction. Unlike hypoxic ventilation, dithionite increased AOS production. Antioxidant enzymes diminished dithionite-induced radical production and diminished the loss of vascular reactivity and lung edema. In conclusion, unlike hypoxic ventilation, dithionite causes edema and loss of vascular reactivity in the lung by generating superoxide anion and hydrogen peroxide. Hypoxia elicited by dithionite is not equivalent to authentic hypoxia because of the obligatory associated generation of AOS. Dithionite usage should not be substituted for authentic hypoxia in studies of O2 sensing.

Animals↗
PubMed1991

A method for preparing analytically pure sodium dithionite. Dithionite quality and observed nitrogenase-specific activities.

Sodium dithionite (Na2S2O4) is widely used as a reductant in biochemical studies, but has not been available in its pure form. A convenient, detailed procedure is given for the recrystallization of commercial dithionite from 0.1 M NaOH-methanol under anaerobic conditions. Twice-recrystallized dithionite had a purity of 99 +/- 1% by UV spectroscopy (A315) and elemental analysis. The influence of dithionite quality on the apparent reduction activities of the nitrogenase components (Av1 and Av2) from Azotobacter vinelandii was investigated.

Crystallization↗
PubMed1999

Anoxic decrease in potassium outward currents of hippocampal cultured neurons in absence and presence of dithionite.

The effect of brief anoxia on voltage dependent K(+)-currents of hippocampal cultured neurons was studied. The oxygen scavenger dithionite (hydrosulphite) was previously used for creating zero oxygen pressure. However, dithionite consumes O(2) in parallel with generation of superoxide radicals and is a strongly reducing agent. In this study anoxia was produced by perfusion of the neurons with a solution bubbled with nitrogen for 1 h using a chamber with an argon layer isolating the anoxic bath flow from atmospheric oxygen in presence and absence of dithionite. Oxygen partial pressure of dithionite-free solution was determined by oxygen dependent quenching of the phosphorescence of Pd-coproporphyrin to be 0.15+/-0. 02 Torr (values are given as mean+/-S.D., n=6). Slow (I(K))- and fast (I(A))-inactivating K(+)-currents were measured with the patch clamp technique in the whole cell configuration. Exposure of the neurons to anoxia reversibly decreased the amplitude of I(K) at a test pulse of 0 mV to 77+/-12% (n=7) in absence and to 83+/-7% (n=6) in presence of 2 mM dithionite; the amplitude of I(A) decreased to 78+/-11% in absence and to 82+/-9% in presence of 2 mM dithionite. Voltage dependence of activation and inactivation shifted 5 min after exposure to anoxia reversibly by about 6 mV in depolarizing direction. The decay times of inactivation were insensitive to anoxia. Dithionite had no significant effects on K(+)-currents. In 15 of 21 neurons not employed for analysis on K(+)-currents, a reversible increase in holding current under dithionite was observed. In absence of dithionite in 4 of 19 neurons the holding current reversibly increased during anoxia. Although dithionite does not affect K(+)-currents, changes in holding current show that the dithionite may affect neurons independently of oxygen deprivation.

Animals↗
PubMed1978

The redox potential of dithionite and SO-2 from equilibrium reactions with flavodoxins, methyl viologen and hydrogen plus hydrogenase.

1. It has been shown that redox equilibria can be formed between dithionite ion (plus SO-2) and (bi)sulphite, and the low-potential electron carriers flavodoxin and methyl viologen. The equilibria were established either by treating the oxidized electron carriers with dithionite, or by treating flavodoxin hydroquinone or methyl viologen semiquinone with (bi)sulphite. Similar redox equilibria were established between dithionite/(bi)sulphite and hydrogen using catalytic amounts of hydrogenase in the presence of a low-potential electron carrier. The effects of pH and temperature on the equilibria were determined. 2. The equilibria were analyzed to determine the redox potential of the dithionite/(bi)sulphite system. In accordance with the results of earlier kinetic studies, it was assumed that the reductant in dithionite solutions is the dissociation product SO-2. The calculated midpoint redox potential E' for the couple SO-2/HSO-3 at pH 7 and 25 degrees C was -0.66 V. The reductant is present largely as the dimer at concentrations of dithionite above about 10nM. Consequently, the midpoint potential, Em, of dithionite solutions becomes less negative as the concentration of dithionite is increased (deltaEm/deltalog S2O2-4 = 29 mV). The theoretical potential of a solution of 1 M S2O2-4 and 2 M (bi)sulphite at pH 7 was calculated to be -0.386V. This value is 59 mV more negative than that determined in 1911 by potentiometry, but considerably more positive than other values in the literature. The effects of pH on the equilibria showed that E' is controlled by the pK of (bi)sulphite at 6.9; the slope deltaE'/deltapH was -59 mV below the pK and -118 mV above the pK. The effects of temperature on the equilibria suggested that Em for dithionite changed by -1.6 mV/degrees C for a rise in temperature between 2 degrees C and 40 degrees C. If sodium dithionite is contaminated with small amounts of (bi)sulphite, its addition in large excess to a low potential electron carrier can cause oxidation of the carrier.

Anaerobiosis↗
PubMed1981

Tetramer-dimer dissociation of carboxyhemoglobin in the absence of dithionite.

The generally accepted value for the tetramer-dimer dissociation constant KL4,2 of carboxyhemoglobin in pH 7.0 phosphate buffer lies in the range 1--2 micrometers. Previous determinations of the quantity have generally involved addition of dithionite to samples to exclude oxygen. We report flash photolysis experiments on carboxyhemoglobin in the absence of dithionite which suggest that KL4,2 is 0.2 +/- 0.05 micrometer. Addition of dithionite to our samples resulted in an order of magnitude increase in KL4,2 in good agreement with previously published results. The mechanism of this increase in dissociation has not been determined with certainty. However, impurities, possibly metal ions, are required in addition to dithionite to produce this effect. Dithionite did not increase KL4,2 for phosphate buffer solutions treated with Chelex 100 analytical grade chelating resin. Addition of bovine serum albumin to untreated buffer solutions before addition of dithionite was found to prevent increased dissociation. The sulfhydryl-reducing agents dithiothreitol and beta-mercaptoethanol were found to protect against the effect of dithionite and to reverse its effect on KL4,2 if they were added after the dithionite. The interaction of the unknown impurities with dithionite to produce increased values of KL4,2 could be mimicked by addition of CU2+ ions in concentrations of less than 1 micrometer to buffer treated with Chelex 100 resin.

Carboxyhemoglobin↗
PubMed2006

Dechlorinating chloroacetanilide herbicides by dithionite-treated aquifer sediment and surface soil.

The prevalent use of chloroacetanilide herbicides has resulted in nonpoint contamination of some groundwater and surface water. We determined the efficacy of dithionite-treated sediment and soils to transform chloroacetanilides. When used alone, dithionite rapidly dechlorinates chloroacetanilides in water, with the following order of reactivity: propachlor > alachlor > acetochlor > metolachlor. Stoichiometric release of chloride occurs during reaction with dithionite, and thiosulfate herbicide derivatives are produced. Treating aquifer sediment with dithionite reduces native Fe(lII), creating a redox barrier of Fe(ll)-bearing minerals and surface-bound Fe(ll). Washing the reduced sediment (buffered with citrate-bicarbonate) with oxygen-free water removed Fe(ll) and excess dithionite and no alachlor transformation was observed. In contrast, a dithionite-treated surface soil, rich in clay and iron, effectively dechlorinated alachlor after washing. Exposing alachlor to aquifer sediment treated with dithionite in potassium carbonate buffer (pH 8.5-9.0) produced dechlorinated alachlor as the major degradation product. Our results provide proof-of-concept that dechlorination of chloroacetanilide herbicides by dithionite and dithionite-treated aquifer sediment and soil is a remediation option in natural environments where iron-bearing minerals are abundant.

Acetamides↗
PubMed1992

The crystal state binding of dithionite to deoxy-hemoglobin.

The crystal state binding of sodium dithionite to deoxyhemoglobin is reported. Dithionite has been used extensively to deoxygenate hemoglobin and myoglobin and there has been considerable interest among users of dithionite about its effect on protein structure and binding site(s). We have determined that dithionite binds to deoxygenated hemoglobin crystals at the interface of two molecules in the crystal lattice. Specific residues involved in hydrogen bonds or salt interactions with dithionite include His116 and His117 of the beta 2 subunit and Lys16 of the alpha 1 subunit of the adjacent hemoglobin molecule. No binding was observed at the symmetry related His116 and 117 beta 1 residues. We have shown that dithionite does not affect the native hemoglobin structure or the binding of several allosteric inhibitors to hemoglobin and can be used to mount T state crystals in the air.

Binding Sites↗
PubMed1975

Reduced diphosphopyridine nucleotide peroxidase. Intermediates formed on reduction of the enzyme with dithionite or reduced diphosphopyridine nucleotide.

DPNH peroxidase is a flavin adenine dinucleotide-containing flavoprotein. Anaerobic titration of enzyme with dithionite has shown that the active site of the enzyme contains 2 mol of flavin and in addition 1 mol of a non-flavin electron acceptor that is tentatively identified as a disulfide group. Thus complete reduction of the enzyme requires 3 mol of dithionite per mole of active site. The first mole of dithionite reduces the non-flavin acceptor; complex formation between the reduced acceptor and one of the bound flavin molecules causes the formation of a long wavelength absorption band between 500 and 670 nm. The second mole of dithionite reduces the flavin that interacts with the reduced non-flavin group, and the long wavelength band disappears. The third mole of dithionite reduces the second mole of flavin. All groups are reoxidized in the presence of air. DPNH reacts with only two of the enzyme-bound electron acceptors. The first mole of DPNH reduces the non-flavin group to form an intermediate (I) that is almost identical with that formed by dithionite. The second mole of DPNH complexes with the second flavin of Intermediate I to form Intermediate II. This reaction causes a further absorbance increase in the long wavelength region; the tail of the absorption band now extends to 960 nm. The titration data (potassium phosphate, 0.05 M, pH 7.0) can be fitted with dissociation constants of 1 times 10-7 M for the formation of I, and 3 times 10-6 M for the conversion of I to II. In air, species II is oxidized to I; I is stable in air, but is oxidized stoichiometrically to oxidized enzyme by H2O2. Present evidence suggests that bound DPN-plus is responsible for the air stability of species I. Intermediate I, but not oxidized enzyme, reacts slowly with phenylmercuric acetate. This reaction causes loss of the air-stable intermediate and parallel loss in enzyme activity. The inactive enzyme cannot be reduced by DPNH to Species I; DPNH can, however, still react with the second flavin to form the autoxidizable complex. With other methods of enzyme inactivation there is also a direct correlation between residual enzyme activity and the ability of enzyme to form the air-stable intermediate. It is concluded that the air-stable intermediate is an important catalytic species.

Anaerobiosis↗
PubMed1980

Fluorescence emission spectra of cells and subcellular preparations of a green photosynthetic bacterium. Effects of dithionite on the intensity of the emission bands.

Fluorescence emission spectra were measured of intact cells and subcellular preparations of the green photosynthetic bacterium Prosthecochloris aestuarii in the presence and in the absence of dithionite. A 3--5-fold increase in bacteriochlorophyll a fluorescence at 816 nm occurred upon addition of dithionite in a membrane vesicle preparation (Complex I), in a photochemically active pigment-protein complex and in a bacteriochlorophyll a protein complex free from reaction centers. The pigment-protein complex showed a relatively strong long-wave emission band (835 nm) of bacteriochlorophyll a, which was preferentially excited by light absorbed at 670 nm and was not stimulated by dithionite. With Complex I, which contains some bacteriochlorophyll c in addition to bacteriochlorophyll a, a 3--4-fold stimulation of bacteriochlorophyll c emission was also observed. Emission bands at shorter wavelengths, probably due to artefacts, were quenched by dithionite. With intact cells, the effect of dithionite was smaller, and consisted mainly of an increase of bacteriochlorophyll a emission. The results indicate that the strong increase in the yield of bacteriochlorophyll emission that occurred upon generating reducing conditions is, at least mainly, due to a direct effect on the light-harvesting systems, and does not involve the reaction center as had been earlier postulated.

Bacteriochlorophylls↗
PubMed1996

Steady-state kinetic studies of dithionite utilization, component protein interaction, and the formation of an oxidized iron protein intermediate during Azotobacter vinelandii nitrogenase catalysis.

Steady-state kinetic analysis of the two-component protein system of Azotobacter vinelandii (Av) nitrogenase is reported. A precisely obeyed half-order reaction in dithionite was observed at concentrations up to 21 mM with no indication of saturation by this substrate. This behavior was monitored by optical, amperometric, and manometric kinetic techniques, and the results were mathematically fit to establish the half-order reaction in dithionite. Under conditions where the MgATP and dithionite concentrations remain unchanged, Av2 (the Fe protein component) interacts with Av1 (the MoFe protein component according to the rate law, suggesting a rapid 1:1 Av2-Av1 interaction: [formula: see text]. with [Av2] the free Fe protein concentration, K = 5.9 microM, and Vmax = 2314 nmol of H2 min-1 (mg of Av1)-1. Under dithionite-depleted conditions, Av2 undergoes an Av1-mediated, one-electron oxidation, consistent with its proposed role as a specific, single-electron reductant for Av1. During steady-state turnover as a function of Av2/Av1 ratio, optical spectroscopy demonstrated the presence of 25-30% oxidized Av2 as an enzyme intermediate. Computer-averaged EPR spectra showed that Av1 was > 95% EPR-silent and Av2 was up to 30% oxidized (Av2ox), consistent with the optical measurements. These optical and EPR results show that up to six Av2ox per Av1 can accumulate in the presence of dithionite during catalysis, suggesting that the conversion of Av2ox back into Av2red is a relatively slow process.

Azotobacter vinelandii↗
PubMed1998

Dithionite quenching rate measurement of the inside-outside membrane bilayer distribution of 7-nitrobenz-2-oxa-1,3-diazol-4-yl-labeled phospholipids.

Measurement of the extent of dithionite quenching of the fluorescence of 7-nitrobenz-2-oxa-1,3-diazol-4-yl- (NBD-) labeled lipids inserted into cellular and organellar membranes has been used to quantify their topological distribution and translocation. This assay provides a straightforward method for determining the fraction of NBD-lipid exposed to the outer leaflet of membranes that are impermeant to dithionite. However, it appears that many, if not all, cellular membranes are relatively permeable to dithionite. The present work describes a method in which the initial rate of dithionite quenching, rather than the extent of quenching, was used to determine the fraction of different NBD-labeled phospholipids exposed to the outer leaflet. This method permits the estimation of the translocation process even in experimental conditions where the membrane is semipermeable to dithionite. This technique was used to measure the translocation of several NBD-labeled phospholipids across two biological membranes: brush border membranes vesicles (BBMV) from rabbit intestine and secretory vesicles (SV) from sec 6-4 mutant yeast cells. BBMV were shown to passively equilibrate N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)monopalmitoylphosphatidylethanolamine (N-NBD-PPE) and 1-palmitoyl-2-[6-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)aminocaproyl]phosphatidylcholine (P-C6-NBD-PC) to approximately 50% in the inner leaflet by a protein-mediated process. In addition, P-C6-NBD-PC was shown to passively equilibrate across SV to approximately 20% in the inner leaflet. The addition of Mg2+ increased the amount on the inner leaflet to approximately 30% by an unknown mechanism, but no evidence for ATP-dependent inward translocation across the SV was found. In the case of BBMV, several different NBD-phospholipids were translocated from the outer to inner leaflet in a matter of minutes and reached an equilibrium distribution of approximately 50% inside and outside. This movement was inhibitable by N-bromosuccinimide. The inward translocation rate and distribution of headgroup labeled N-NBD-lysophosphatidylethanolamine, having one titratable negative charge, was increased in the presence of an inward basic pH gradient. The same NBD-phospholipids were also translocated across SV to roughly 50% in both leaflets with the exception of NBD-phosphatidic acid, which was passively distributed with 80% in the inner leaflet.

Animals↗
PubMed1985

Kinetics of reduction of cytochrome c oxidase by dithionite and the effect of hydrogen peroxide.

The reduction of cytochrome c oxidase by dithionite was reinvestigated with a flow-flash technique and with varied enzyme preparations. Since cytochrome a3 may be defined as the heme in oxidase which can form a photolabile CO adduct in the reduced state, it is possible to follow the time course of cytochrome a3 reduction by monitoring the onset of photosensitivity. The onset of photosensitivity and the overall rate of heme reduction were compared for Yonetani and Hartzell-Beinert preparations of cytochrome c oxidase and for the enzyme isolated from blue marlin and hammerhead shark. For all of these preparations the faster phase of heme reduction, which is dithionite concentration-dependent, is almost completed when the fraction of photosensitive material is still small. We conclude that cytochrome a3 in the resting enzyme is consistently reduced by an intramolecular electron transfer mechanism. To determine if this is true also for the pulsed enzyme, we examined the time course of dithionite reduction of the peroxide complex of the pulsed enzyme. It has been previously shown that pulsed cytochrome c oxidase can interact with H2O2 and form a stable room temperature peroxide adduct (Bickar, D., Bonaventura, J., and Bonaventura, C. (1982) Biochemistry 21, 2661-2666). Rather complex kinetics of heme reduction are observed when dithionite is added to enzyme preparations that contain H2O2. The time courses observed provide unequivocal evidence that H2O2 can, under these conditions, be used by cytochrome c oxidase as an electron acceptor. Experiments carried out in the presence of CO show that a direct dithionite reduction of cytochrome a3 in the peroxide complex of the pulsed enzyme does not occur.

Animals↗
PubMed1992

Evidence of dithionite contribution to the low-frequency resonance Raman spectrum of reduced and mixed-valence cytochrome c oxidase.

The resonance Raman spectra of deoxygenated solutions of mixed-valence cyanide-bound and fully reduced cytochrome oxidase derivatives that have been reduced in the presence of aqueous or solid sodium dithionite exhibit two new low-frequency lines centered at 474 and 590 cm-1. These lines were not observed when the reductant system was changed to a solution containing ascorbate and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). Under enzyme turnover conditions, the addition of dithionite to the reoxidized protein (the 428-nm or "oxygenated" form) increases the intensity of these lines, while reoxidation and rereduction of the enzyme in the presence of ascorbate/TMPD resulted in the absence of both lines. Our data suggest that both lines must have contributions from species formed from aqueous dithionite, presumably the SO2 species, since these two lines are also observed in the Raman spectrum of a solution of aqueous dithionite, but not in the spectrum of an ascorbate/TMPD solution. Since heme metal-ligand stretch vibrations are expected to appear in the low-frequency region from 215 to 670 cm-1, our results indicate that special care should be exercised during the interpretation of the cytochrome a3 resonance Raman spectrum.

Animals↗
PubMed1986

Kinetic studies of the reduction of neutrophil cytochrome b-558 by dithionite.

The reduction with dithionite of neutrophil cytochrome b-558, implicated in superoxide generation by activated neutrophils, was investigated by a stopped-flow technique in non-ionic-detergent extracts of the membranes and in crude membrane particles. The dependence of the pseudo-first-order rate constants on the concentration of dithionite was consistent with a mechanism of reduction that involves the dithionite anion monomer SO2.- as the reactive species. The estimated second-order rate constant was 7.8 X 10(6) M-1 X S-1 for Lubrol PX-solubilized cytochrome b-558 and 5.1 X 10(6) M-1 X S-1 for the membrane-bound protein. The similarity of the kinetic constants suggests that solubilization did not introduce gross changes in the reactive site. Imidazole and p-chloromercuribenzoate, known as inhibitors of NADPH oxidase, did not affect significantly cytochrome b-558 reduction rates. The reaction rate of cytochrome b-558 with dithionite exhibited a near-zero activation energy. The first-order rate constant for reduction decreased with increasing ionic strength, indicating a positive effective charge on the reacting protein.

Chloromercuribenzoates↗
PubMed2000

Effects of hypoxia and dithionite on catecholamine release from isolated type I cells of the rat carotid body.

1. Amperometric recordings were conducted to investigate the ability of hypoxia and anoxia to evoke quantal catecholamine secretion from isolated type I cells of the rat carotid body. 2. Hypoxia (PO2 8-14 mmHg) consistently failed to evoke catecholamine secretion from type I cells, when cells were perfused either at room temperature (21-24 C) or at 35-37 C, and regardless of whether Hepes- or HCO3-/CO2-buffered solutions were used. 3. Elevating extracellular [K+] caused concentration-dependent secretion from individual type I cells, with a threshold concentration of approximately 25 mM. In the presence of this level of extracellular K+, hypoxia (PO2 8-14 mmHg) caused a marked enhancement of secretion which was fully blocked by 200 microM Cd2+, a non-specific blocker of voltage-gated Ca2+ channels. 4. Anoxia (N2-equilibrated solution containing 0.5 mM dithionite) evoked exocytosis from type I cells when extracellular [K+] was 5 mM. This secretion was completely inhibited by removal of extracellular Ca2+, but was not significantly affected by Cd2+ (200 microM), Ni2+ (2 mM), Zn2+ (1 mM) or nifedipine (2 microM). Secretion was also observed when 0.5 mM dithionite was added to air-equilibrated solutions. 5. Anoxia also evoked secretion from chemoreceptive phaeochromocytoma (PC12) cells, which was wholly Ca2+ dependent, but unaffected by Cd2+ (200 microM). 6. Our results suggest that hypoxia can evoke catecholamine secretion from isolated type I cells, but only in the presence of elevated extracellular [K+]. This may be due to the cells being relatively hyperpolarized following dissociation. In addition, we have shown that dithionite evokes catecholamine release regardless of PO2 levels, and this release is due mainly to an artefactual Ca2+ influx pathway activated in the presence of dithionite.

Animals↗
PubMed1990

Dithionite treatment of flavins: spectral evidence for covalent adduct formation and effect on in vitro bacterial bioluminescence.

Intrigued by the apparent requirement of dithionite for FMN reduction (as opposed to photoreduction or catalytic hydrogenation) in the H2O2-initiated bacterial bioluminescence reaction, we chose 5-ethyl-3-methyllumiflavinium cation I as a model to investigate possible flavin adduct formation by treatment with dithionite or (bi)sulfite. In the range of pH 5-8, the reaction of dithionite with 5-ethyl-3-methyllumiflavinium cation, which is in equilibrium with the 5-ethyl-4a-hydroxy-3-methyl-4a, 5-dihydrolumiflavin pseudobase II (X = OH), is not limited to the formation of flavosemiquinone and dihydroflavin following two one-electron steps. Several parallel and sequential reactions may take place involving the intermediacy of covalent flavin adducts. Addition of (bi)sulfite gave a 4a-sulfiteflavin adduct II (X = SO3-). Consistent with the S2O4(2-) in equilibrium with 2 SO2-. equilibrium, the reaction of dithionite and II (X = OH; SO3-) gave rise to two flavin adducts in competitive nucleophilic displacements: a 4a-sulfoxylate-flavin radical (II, X = SO2.) and a 4a-dithioniteflavin adduct (II, X = S2O4-), respectively. On increasing the (S2O4(2-), SO2.-)/flavin ratio under N2, the formation of the 4a-sulfoxylate-flavin radical became predominant. The II (X = SO2.) so formed was in equilibrium with the flavosemiquinone and bisulfate and can be trapped by reacting with hydroxylamine. In the initial presence of oxygen, II (X = SO2.) was highly reactive toward O2, giving a fast oxidation to II (X = SO3-) and effectively suppressing the formation of the flavosemiquinone.(ABSTRACT TRUNCATED AT 250 WORDS)

Dithionite↗