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At least 109 records · Page 6Linked to original sources
PubMed1992

X-ray absorption studies of the Cu-dependent phenylalanine hydroxylase from Chromobacterium violaceum. Comparison of the copper coordination in oxidized and dithionite-reduced enzymes.

The coordination chemistry of the Cu sites of phenylalanine hydroxylase (PAH) from Chromobacterium violaceum has been studied by X-ray absorption spectroscopy (XAS). The EXAFS of the Cu(II) form of the enzyme resembles that of other non-blue copper proteins such as plasma amine oxidases and dopamine-beta-hydroxylase and is characteristic of a mixed N/O coordination shell containing histidine ligation. Detailed simulations of the raw EXAFS data have been carried out using full curved-wave restrained refinement methodologies which allow imidazole ligands to be treated as structural units. The results suggest a Cu(II) coordination of two histidines and two additional O/N-donor groups. A reasonable fit to both data sets can be obtained by assuming that the non-imidazole first-shell donor atoms are derived from solvent (H2O or OH-). The EXAFS of the reduced enzyme shows major differences. The amplitude of the first shell in the Fourier transform is only 50% of that of the oxidized enzyme, indicative of a substantial reduction in coordination number. In addition, the first shell of the transform is split into two components. Simulations of the reduced data can be obtained by either two histidines at a long distance of 2.08 A and an O ligand at a short distance of 1.88 A or two histidines at a short distance of 1.90 A and one second-row scatterer such as S or Cl at 2.20 A. Comparison of absorption edge data on the reduced enzyme with data from Cu(I) bis- and tris(1,2-dimethylimidazole) complexes suggests a pseudo-three-coordinate structure.

Chromobacterium↗
PubMed1977

Kinetics of dithionite ion utilization and ATP hydrolysis for reactions catalyzed by the nitrogenase complex from Azotobacter vinelandii.

The kinetics of S2O42-utilization and ATP hydrolysis during the nitrogenase-catalyzed H2 evolution and acetylene and nitrogen-reducing reactions were studied using a polarographic technique to monitor-S2O42-concentration. Rate constants for both S2O42-utilization and ATP hydrolysis were determined as a function of temperature and corresponding activation energies determined. The activation energy for ATP hydrolysis differs from that for product formation or S2O42-utilization by 5 kcal/mol above 20 degrees C and by 25 kcal/mol below 20 degrees C. The rate law for S2O42-utilization was determined and describes the enzyme catalyzed rate over a 1000-fold variation in S2O42-concentration and at least a 100-fold change in ATP concentration. The rate law for S2O42-utilization under N2-reducing conditions at 25 degrees C is given by -d([S2O42-]/dt = (2.3 x 10(-3) ET[S2O42-]1/2-[ATP]2)/([ATP]2 + K1[ATP] + K2), where ET is total enzyme concentration in mg/ml and K1 and K2 are equilibrium constants for ATP binding to nitrogenase. The half-order dependence of the rate on S2O42-concentration in interpreted in terms of the equilibrium S2O42- = 2SO2-, in which SO2- is the actual electron donor to nitrogenase. A partial mechanism incorporating these results is presented.

Acetobacter↗
PubMed2005

Treatment of hexavalent chromium in chromite ore processing solid waste using a mixed reductant solution of ferrous sulfate and sodium dithionite.

We investigated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in chromite ore processing solid waste (COPSW) derived from the production of ferrochrome alloy. The COPSW is characterized by high pH (8.5-11.5) and high Cr(VI) concentrations in the solid phase (up to 550 mg kg(-1)) and dissolved phase (3-57 mg L(-1)). The dominant solid-phase minerals are forsterite (Mg2SiO4), brucite (Mg-(OH)2), and hydrocalumite [Ca4(Al, Fe)2(OH)12X x 6H2O), X = (OH)2(2-), SO4(2-), CrO4(2-)]. The method utilizes FeSO4 in combination with Na2S2O4 to inhibit oxidation and precipitation of the ferrous iron, thereby preventing well and formation clogging. Laboratory batch tests using a 0.05 M FeSO4 + 0.05 M Na2S2O4 solution indicated effective treatment of both dissolved and solid-phase Cr(VI). Contrary to treatments with FeSO4 and FeCl2 alone, the combination resulted in both complete removal of Cr(VI) from solution and sustained Fe(ll) concentrations in solution after a 24 h period. A field test involving injection of 5700 L of a 0.07 M FeSO4 + 0.07 M Na2S2O4 solution into a COPSW saturated zone (pH 11.5) indicated no well and formation clogging during injection. Examination of a core collected 0.46 m from the injection well following injection indicated effective treatment of the solid phase Cr(VI) based on analysis of water, phosphate solution, and high temperature alkaline extracts. The combined reductant solution also imparted a residual treatment capacity to the COPSW allowing for subsequent treatment of dissolved phase Cr(VI); however, dissemination of the iron in the highly alkaline environment appeared to be impeded by the inability to sufficiently lower the pH with distance from the injection well to avoid precipitation of Fe(OH)2 and likely also FeCO3. Injection of a 0.2 M FeSO4 + 0.2 M Na2S2O4 solution into another COPSW saturated zone (pH 9) indicated much more effective dissemination of the injected iron.

Carcinogens, Environmental↗
PubMed1975

The thermochemical characterization of sodium dithionite, flavin mononucleotide, flavin-adenine dinucleotide and methyl and benzyl viologens as low-potential reductants for biological systems.

The heat of reaction (deltaH) of Fe(CN)63-, Methyl Viologen, FMN and FAD with S2O42- in aqueous buffer solutions was measured calorimetrically. In addition deltaH values for reduction of Fe(CN)63-, FMN and FAD by reduced Methyl Viologen were determined. The resulting calorimetric data and corresponding E0 values were combined to yield thermodynamic data for these simple reducing agents in a form useful for applications to biological reactions. Thermodynamic data for the reduction of spinach ferredoxin are also presented.

Calorimetry↗
PubMed1984

The mechanism of Klebsiella pneumoniae nitrogenase action. Simulation of the dependences of H2-evolution rate on component-protein concentration and ratio and sodium dithionite concentration.

The rate constants from Table 1 and Scheme 2 of Lowe & Thorneley [(1984) Biochem. J. 224, 877-886] were used to simulate the rate of H2 evolution, under various conditions, from nitrogenase isolated from Klebsiella pneumoniae. These rates depend on both the ratio and concentrations of the MoFe protein and Fe protein that comprise nitrogenase. The simulations explain the shapes of 'protein titration' and 'dilution effect' curves. The concept of an apparent Km for the reductant Na2S2O4 is shown to be invalid, since the dependence of H2-evolution rate on the square root of S2O4(2-) concentration is not hyperbolic and depends on the ratio and absolute concentrations of the MoFe protein and Fe protein.

Dithionite↗
PubMed1981

99mTc-labelled compounds prepared with sodium dithionite as reducing agent.

The paper deals with the applications of Na2S2O4 as reducing agent in the preparation of 99mTc-labelled compounds. The reduction of pertechnetate can advantageously be carried out in neutral solutions of pH 7. Using this procedure, DTPA, HEDSPA, MDP, gluconate, citrate and trypsin were successfully labelled. In HEDSPA and MDP labelling, a high as cumulation of 99mTc in rat bones (50%) was obtained. In gluconate labelling, under various reaction temperatures, two types of complexes were prepared. Complex I shows a 99mTc biodistribution which is comparable with the kidney diagnosticum 99mTc-Sn-gluconate (24% of 99mTc in kidneys). Complex II, on the other hand, exhibited a reduced affinity of 99mTc to kidneys (2.2%) which, however, increases in bone to 15.4%. The experimental results indicated that Tc(V) is bound in Complex I. In technetium complexing no "mixed complex" is formed technetium being complexed directly by chelate-forming groups on the labelled compound.

Animals↗