scholarly journals Contributions to Cytochrome c Inner- and Outer-Sphere Reorganization Energy

2021 ◽  
Author(s):  
Samir Chattopadhyay ◽  
Manjistha Mukherjee ◽  
Banu Kandemir ◽  
Sarah Bowman ◽  
Kara L Bren ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Energy Conversion ◽  
Reorganization Energy ◽  
Outer Sphere ◽  
Water Soluble ◽  
Small Water ◽  
Cytochromes C ◽  
Cytochrome C552 ◽  
Hydrogenobacter Thermophilus

Cytochromes c are small water-soluble proteins that catalyze electron transfer in metabolism and energy conversion processes. Hydrogenobacter thermophilus cytochrome c552 presents a curious case in displaying fluxionality of its heme...

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.

scholarly journals Variation of the axial haem ligands and haem-binding motif as a probe of the Escherichia coli c-type cytochrome maturation (Ccm) system

2003 ◽  
Vol 375 (3) ◽  
pp. 721-728 ◽  
Author(s):  
James W. A. ALLEN ◽  
Stuart J. FERGUSON
Keyword(s):  
Escherichia Coli ◽  
Cytochrome C ◽  
Covalent Attachment ◽  
Binding Motif ◽  
Cytochrome C Maturation ◽  
Cytochromes C ◽  
Cytochrome C552 ◽  
Haem Iron ◽  
Made In ◽  
Uncatalysed Reaction

Cytochromes c are typically characterized by the covalent attachment of haem to polypeptide through two thioether bonds with the cysteine residues of a Cys-Xaa-Xaa-Cys-His peptide motif. In many Gram-negative bacteria, the haem is attached to the polypeptide by the periplasmically functioning cytochrome c maturation (Ccm) proteins. Exceptionally, Hydrogenobacter thermophilus cytochrome c552 can be expressed as a stable holocytochrome both in the cytoplasm of Escherichia coli in an apparently uncatalysed reaction and also in the periplasm in a Ccm-mediated reaction. In the present study we show that a Met60→Ala variant of c552, which does not have the usual distal methionine ligand to the haem iron of the mature cytochrome, can be made in the periplasm by the Ccm system. However, no holocytochrome could be detected when this variant was expressed cytoplasmically. These data highlight differences between the two modes of cytochrome c assembly. In addition, we report investigations of haem attachment to cytochromes altered to have the special Cys-Trp-Ser-Cys-Lys haem-binding motif, and Cys-Trp-Ser-Cys-His and Cys-Trp-Ala-Cys-His analogues, of the active-site haem of nitrite reductase NrfA.

scholarly journals Distal [FeS]-Cluster Coordination in [NiFe]-Hydrogenase Facilitates Intermolecular Electron Transfer

2017 ◽  
Author(s):  
Alexander Petrenko ◽  
Matthias Stein
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Electric Energy ◽  
Reorganization Energy ◽  
Outer Sphere ◽  
Intermolecular Electron Transfer ◽  
Sulfur Cluster ◽  
Donor And Acceptor ◽  
Marcus Equation ◽  
Hydrogenase Enzyme

Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron–sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron–sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering.

scholarly journals The photo-physical study of the interaction of riboflavin with Nicotine in bicontinuous microemulsion

2017 ◽  
Vol 6 (6) ◽  
pp. 267-275
Author(s):  
Maurice Ohaekeleihem Iwunze
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Rate Constant ◽  
Reorganization Energy ◽  
Outer Sphere ◽  
Electron Transfer Reaction ◽  
Microemulsion System ◽  
Quenching Rate ◽  
Bicontinuous Microemulsion ◽  
Bimolecular Quenching

Steady-state fluorescence spectroscopy was used to study the interaction of riboflavin with nicotine in a bicontinuous microemulsion system made up of 42.11:13.70:21.34:22.85 % w/w of water: oil: surfactant: cosurfactant. The surfactant used is cetyltrimethylammonium bromide (CTAB), the oil is tetradecane and the cosurfactant is 1-pentanol. It is observed that the interaction of riboflavin and nicotine in the prepared microemulsion lead to the quenching of riboflavin fluorescence. The bimolecular quenching rate constant, kq, of riboflavin by nicotine was observed as 4.15 x 109 M-1 s -1 with an efficiency of 56 %. The mechanism of the reaction is proposed to be diffusion limited in an activated electron transfer reaction in a solvent separated (outer-sphere) scheme. The electron transfer rate constant, kET, was calculated as 5.89 x 109 s -1 with an activation rate constant, ka, of 9.52 x 109 s -1 . The calculated solvent reorganization energy, λs, of the reaction was 1.09 eV, the free energy of interaction, ΔGo , is -2.9 eV and the free energy of activation, ΔG*, was calculated as 0.75 eV.

Pressure Tuning Voltammetry. Reaction Volumes for Electron Transfer in Cytochrome c and Ruthenium-Modified Cytochromes c

1995 ◽  
Vol 117 (9) ◽  
pp. 2600-2605 ◽  
Author(s):  
J. Sun ◽  
J. F. Wishart ◽  
R. van Eldik ◽  
R. D. Shalders ◽  
T. W. Swaddle
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Pressure Tuning ◽  
Cytochromes C ◽  
Reaction Volumes

scholarly journals Amino Acid Substitutions in the Non-Ordered Ω-Loop 70–85 Affect Electron Transfer Function and Secondary Structure of Mitochondrial Cytochrome c

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 973
Author(s):  
Rita V. Chertkova ◽  
Tatyana V. Bryantseva ◽  
Nadezhda A. Brazhe ◽  
Kseniya S. Kudryashova ◽  
Victor V. Revin ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Secondary Structure ◽  
Cytochrome C ◽  
Cd Spectroscopy ◽  
Mitochondrial Cytochrome ◽  
Proposed Model ◽  
Donor And Acceptor ◽  
Cytochromes C ◽  
Spectroscopy Studies ◽  
Mitochondrial Cytochrome C

The secondary structure of horse cytochrome c with mutations in the P76GTKMIFA83 site of the Ω-loop, exhibiting reduced efficiency of electron transfer, were studied. CD spectroscopy studies showed that the ordering of mutant structure increases by 3–6% compared to that of the WT molecules due to the higher content of β-structural elements. The IR spectroscopy data are consistent with the CD results and demonstrate that some α-helical elements change into β-structures, and the amount of the non-structured elements is decreased. The analysis of the 1H-NMR spectra demonstrated that cytochrome c mutants have a well-determined secondary structure with some specific features related to changes in the heme microenvironment. The observed changes in the structure of cytochrome c mutants are likely to be responsible for the decrease in the conformational mobility of the P76GTKMIFA83 sequence carrying mutations and for the decline in succinate:cytochrome c-reductase and cytochrome c-oxidase activities in the mitoplast system in the presence of these cytochromes c. We suggest that the decreased efficiency of the electron transfer of the studied cytochromes c may arise due to: (1) the change in the protein conformation in sites responsible for the interaction of cytochrome c with complexes III and IV and (2) the change in the heme conformation that deteriorates its optimal orientation towards donor and acceptor in complexes III and IV therefore slows down electron transfer. The results obtained are consistent with the previously proposed model of mitochondrial cytochrome c functioning associated with the deterministic mobility of protein globule parts.

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