scholarly journals Kinetics of Reduction of Fe(III) Complexes by Outer Membrane Cytochromes MtrC and OmcA of Shewanella oneidensis MR-1

2008 ◽  
Vol 74 (21) ◽  
pp. 6746-6755 ◽  
Author(s):  
Zheming Wang ◽  
Chongxuan Liu ◽  
Xuelin Wang ◽  
Matthew J. Marshall ◽  
John M. Zachara ◽  
...  
Keyword(s):  
Redox Potential ◽  
Outer Membrane ◽  
Kinetic Data ◽  
Shewanella Oneidensis ◽  
Reorganization Energy ◽  
Second Order ◽  
Metal Species ◽  
Stopped Flow ◽  
Kinetics Of ◽  
Kinetics Of Reduction

ABSTRACT Because of their cell surface locations, the outer membrane c-type cytochromes MtrC and OmcA of Shewanella oneidensis MR-1 have been suggested to be the terminal reductases for a range of redox-reactive metals that form poorly soluble solids or that do not readily cross the outer membrane. In this work, we determined the kinetics of reduction of a series of Fe(III) complexes with citrate, nitrilotriacetic acid (NTA), and EDTA by MtrC and OmcA using a stopped-flow technique in combination with theoretical computation methods. Stopped-flow kinetic data showed that the reaction proceeded in two stages, a fast stage that was completed in less than 1 s, followed by a second, relatively slower stage. For a given complex, electron transfer by MtrC was faster than that by OmcA. For a given cytochrome, the reaction was completed in the order Fe-EDTA > Fe-NTA > Fe-citrate. The kinetic data could be modeled by two parallel second-order bimolecular redox reactions with second-order rate constants ranging from 0.872 μM−1 s−1 for the reaction between MtrC and the Fe-EDTA complex to 0.012 μM−1 s−1 for the reaction between OmcA and Fe-citrate. The biphasic reaction kinetics was attributed to redox potential differences among the heme groups or redox site heterogeneity within the cytochromes. The results of redox potential and reorganization energy calculations showed that the reaction rate was influenced mostly by the relatively large reorganization energy. The results demonstrate that ligand complexation plays an important role in microbial dissimilatory reduction and mineral transformation of iron, as well as other redox-sensitive metal species in nature.

THE REDUCTION OF CYTOCHROMEcBY HYDROQUINONE

1963 ◽  
Vol 41 (1) ◽  
pp. 231-237 ◽  
Author(s):  
G. R. Williams
Keyword(s):  
Reaction Mechanism ◽  
Ionic Strength ◽  
Rate Equation ◽  
Second Order ◽  
Order Rate ◽  
Ferricytochrome C ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
Order Rate Equation

The kinetics of reduction of ferricytochrome c by hydroquinone have been studied. The reaction does not conform to a simple second-order rate equation and it is demonstrated that the deviations are brought about by the presence of p-quinone, one of the products of the reaction. The accelerating effect of p-quinone is explained tentatively on the basis of an involvement of the semi-quinone. The effects on the reaction of pH, ionic strength, and temperature are reported and used to suggest features of the reaction mechanism.

Kinetics of N-substituted phenothiazines and N-substituted phenoxazines oxidation catalyzed by fungal laccases

2009 ◽  
Vol 4 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Lidija Tetianec ◽  
Juozas Kulys
Keyword(s):  
Electron Transfer ◽  
Redox Potential ◽  
Reorganization Energy ◽  
Outer Sphere ◽  
Initial Reaction Rate ◽  
Initial Reaction ◽  
Type I ◽  
Electron Transfer Mechanism ◽  
Recombinant Laccase ◽  
Kinetics Of

AbstractLaccase-catalyzed oxidation of N-substituted phenothiazines and N-substituted phenoxazines was investigated at pH 5.5 and 25°C. The recombinant laccase from Polyporus pinsitus (rPpL) and the laccase from Myceliophthora thermophila (rMtL) were used. The dependence of initial reaction rate on substrate concentration was analyzed by applying the laccase action scheme in which the laccase native intermediate (NI) reacts with a substrate forming reduced enzyme. The reduced laccase produces peroxide intermediate (PI) which in turn decays to the NI. The calculated constant (kox) values of the PI formation are (6.1±3.1)×105 M−1s−1 for rPpL and (2.5±0.9)×104 M−1s−1 for rMtL. The bimolecular constants of the reaction of the native intermediate with electron donor (kred) vary in the interval from 2.2×105 to 2.1×107 M−1s−1 for rPpL and from 1.3×102 to 1.8×105 M-1s−1 for rMtL. The larger reactivity of rPpL in comparison to rMtL is associated with the higher redox potential of type I Cu of rPpL. The variation of kred values for both laccases correlates with the change of the redox potential of substrates. Following outer sphere (Marcus) electron transfer mechanism the calculated activationless electron transfer rate and the apparent reorganization energy are 5.0×107 M−1s−1 and 0.29 eV, respectively.

Ruthenium and iron complexes of dipicolinic acid: Synthesis, solution properties and kinetics of electron transfer reactions with ascorbate ions

1983 ◽  
Vol 36 (12) ◽  
pp. 2377 ◽  
Author(s):  
NH Williams ◽  
JK Yandell
Keyword(s):  
Redox Potential ◽  
Rate Constant ◽  
Dipicolinic Acid ◽  
Acid Synthesis ◽  
Equilibrium Mixture ◽  
A Value ◽  
Inert Electrode ◽  
Ph Range ◽  
Kinetics Of ◽  
Kinetics Of Reduction

Standard potentials of the redox couples [bis(pyridine-2,6-dicarboxylate)MIII]-/2- ([M(dipic)2]-/2-, where M = Fe, Ru, Co) have been determined at 25�C, and ionic strength 0.1M (NaClO4 or KNO3). Kinetics of reduction of the oxidized complexes by ascorbate have also been examined under the same conditions. The [Fe(dipic)2]-/2- potential was found to be 355 � 5 mV. Reduction of [Fe(Fe(dipic)2]- in the pH range 4-6 was shown to occur by reaction with ascorbate monoanion (HA-) with a rate constant of (2.2 � 0.2) × 103 1. mol-1 s-1, and ascorbate dianion(A2-) with a rate constant of (7 � 1) × 108 1. mol-1 s-1. K [Ru(dipic)2] has been synthesized. Spectroscopic and analytical evidence suggest that it is a simple six-coordinate species in the solid and in non-aqueous solvents, but that in water it exists as an equilibrium mixture of at least two species. The redox potential for this mixture was found to be 270 � 10 mV. The major component of this mixture is reduced by A2- with a rate constant of (4.7 � 0.1) × 1081.mol-1 s-1. A value of 747 � 5 mV was measured for the redox potential of the cobalt couple, although equilibration of this system with the inert electrode could be achieved only by using [Fe(bpy)2(CN)2] as a mediator. Kinetics of reduction of [Co(dipic)2]- by ascorbate were complex and not reproducible.

THE REDUCTION OF CYTOCHROMEcBY HYDROQUINONE

1963 ◽  
Vol 41 (1) ◽  
pp. 231-237 ◽  
Author(s):  
G. R. Williams
Keyword(s):  
Reaction Mechanism ◽  
Ionic Strength ◽  
Rate Equation ◽  
Second Order ◽  
Order Rate ◽  
Ferricytochrome C ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
Order Rate Equation

The kinetics of reduction of ferricytochrome c by hydroquinone have been studied. The reaction does not conform to a simple second-order rate equation and it is demonstrated that the deviations are brought about by the presence of p-quinone, one of the products of the reaction. The accelerating effect of p-quinone is explained tentatively on the basis of an involvement of the semi-quinone. The effects on the reaction of pH, ionic strength, and temperature are reported and used to suggest features of the reaction mechanism.

The kinetics of the reaction of boric acid with salicylic acid

1977 ◽  
Vol 55 (16) ◽  
pp. 3035-3039 ◽  
Author(s):  
Alan Queen
Keyword(s):  
Salicylic Acid ◽  
Boric Acid ◽  
Kinetic Data ◽  
Similar Process ◽  
Stopped Flow ◽  
Ph Values ◽  
The Stability ◽  
Kinetics Of ◽  
Protonated Ligand ◽  
Salicylate Ion

Salicylic acid forms a 1:1 complex with boric acid, the reaction involving both the fully protonated ligand, and the salicylate ion. The kinetics of this reaction have been studied by the stopped-flow method. The stability constant for the reaction involving salicylate ion has been calculated from measurements of the absorbances of solutions at equilibrium and is the same as that obtained from the kinetic data. The kinetic results at pH values in the range 3.45–4.63 suggest that, when salicylic acid is the ligand, the complex is formed in two steps. A similar process may also occur with salicylate ions.

Outer-sphere electron transfer reactions of aqua(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato) nickel(II) and (III).

2003 ◽  
Vol 81 (2) ◽  
pp. 186-192 ◽  
Author(s):  
Robert I Haines ◽  
Dean R Hutchings
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Outer Sphere ◽  
Second Order ◽  
Marcus Theory ◽  
Pendant Arm ◽  
Key Words Nickel ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
Sphere Mechanism

The outer-sphere oxidation of the nickel(II) complex of the deprotonated pendant-arm macrocycle, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate, [NiL1(OH2)]+ by bis-(1,4,7-triazacyclononane)nickel(III), [Ni(tacn)2]3+ has been studied in aqueous perchlorate media. The reaction displays reversible second-order behaviour and the kinetic study reveals the forward and reverse rate constants for the reaction: [Formula: see text] The kinetics show the forward reaction to be acid dependent, a feature that is attributed to protonation of the acetato group of the nickel(II) complex. Using Marcus theory, the self-exchange rate for the [NiL1(OH2)]+/2+ couple has been calculated. The nickel(II/III) electron transfer is a reversible one electron process with E° = 1.04 V (vs. S.H.E.). The formation of the authentic nickel(III) product has been confirmed by esr spectroscopy. The kinetics of reduction of the [NiL1(OH2)]2+ species by Fe2+(aq) exhibits a second-order rate law, the reaction being independent of acid. Using the calculated self-exchange rate for the nickel complex, its reaction with Fe2+(aq) has been examined in terms of an inner- versus outer-sphere mechanism. Key words: nickel(III), pendant-arm macrocycles, hexaaquairon(II), outer sphere, kinetics, Marcus theory.

scholarly journals Stopped-flow spectrophotometric studies on the reaction of turkey liver xanthine dehydrogenase with reducing substrates

1978 ◽  
Vol 171 (1) ◽  
pp. 83-88 ◽  
Author(s):  
Í N Fhaoláin ◽  
M J Hynes ◽  
M P Coughlan
Keyword(s):  
Active Site ◽  
Rate Constants ◽  
Xanthine Dehydrogenase ◽  
Stopped Flow ◽  
Redox Potentials ◽  
First Order ◽  
The Third ◽  
Enzyme Functionality ◽  
Kinetics Of ◽  
Kinetics Of Reduction

The kinetics of reduction of turkey liver xanthine dehydrogenase by substrates were investigated by stopped-flow spectrophotometry. The results may be explained in terms of the known redox potentials of the various centres in the enzyme [Barber, Bray, Cammack & Coughlan (1977) Biochem. J. 163, 279-289]. They are, morover, consistent with the scheme [Olson, Ballou, Palmer & Massey (1974) J. Biol. Chem. 249, 4363-4382] in which reduction occurs in three consecutive steps, one molecule of substrate reacting with the active site at each step. First-order rate constants believed to correspond respectively to the combined first and second steps and to the third step in the reduction by excess of xanthine and of NADH were determined. The rates of reaction with these substrates in the combined first and second steps are independent of the degree of enzyme functionality.

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

1990 ◽  
Vol 68 (4) ◽  
pp. 537-542 ◽  
Author(s):  
John W. Bunting ◽  
M. Morgan Conn
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Ph Dependence ◽  
Second Order ◽  
Order Rate ◽  
Heteroaromatic Cation ◽  
Absolute Magnitudes ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
Dihydropyridine Derivatives

The pH-dependences of the apparent second-order rate constants [Formula: see text] for the reduction of 2,4,6-cycloheptatrien-1-ol and 9-xanthydrol by each of 1-benzyl-1,4-dihydronicotinamide (BNH) and 10-methyl-9,10-dihydroacridine (MAH) have been measured in 20% acetonitrile – 80% water, at 25 °C and ionic strength 1.0. For each of these reactions, the pH-dependence of [Formula: see text] is only consistent with reduction occurring via the aromatic cation (either tropylium or xanthylium) that is present in equilibrium with these alcoholic species. The relative second-order rate constants [Formula: see text] for reductions by these two reducing agents (1700 for tropylium and 770 for xanthylium) are similar for these two cations. These ratios are also similar to those observed for a variety of nitrogen heteroaromatic hydride acceptors, even though the absolute magnitudes of these rate constants vary by 1010-fold. The second-order rate constants for the reductions of the tropylium and xanthylium cations are predicted reasonably well by their [Formula: see text] values, with the latter cation being (7 × 105)-fold more reactive than its π-isoelectronic N-methyl acridinium cation. The xanthylium cation has the greatest [Formula: see text] ratio yet observed for any heteroaromatic cation, and this value further extends the known range of this ratio as a function of reactivity. Keywords: hydride transfer, kinetics of reduction, 1,4-dihydropyridine derivatives, tropylium cation, xanthylium cation.

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