Electrochemical redox transformations of T1 and T2 copper sites in native Trametes hirsuta laccase at gold electrode

Mediatorless, electrochemically driven, redox transformations of T1 (type 1) and T2 copper sites in Trametes hirsuta laccase were studied by cyclic voltammetry and spectroelectrochemical redox titrations using bare gold electrode. DET (direct electron transfer) between the electrode and the enzyme was observed under anaerobic conditions. From analysis of experimental data it is concluded that the T2 copper site is in DET contact with gold. It was found that electron transfer between the gold surface and the T1 copper site progresses through the T2 copper site. From EPR measurements and electrochemical data it is proposed that the redox potential of the T2 site for high-potential ‘blue’ laccase is equal to about 400 mV versus NHE (normal hydrogen electrode) at pH 6.5. The hypothesis that the redox potentials of the T2 copper sites in low- and high-potential laccases/oxidases from totally different sources might be very similar, i.e. approx. 400 mV, is discussed.

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Characterization of Mercaptoethylamine-Modified Gold Electrode Surface and Analyses of Direct Electron Transfer to Putidaredoxin

Langmuir ◽

10.1021/la00012a038 ◽

1995 ◽

Vol 11 (12) ◽

pp. 4818-4822 ◽

Cited By ~ 16

Author(s):

Ling Sang Wong ◽

Vincent L. Vilker ◽

William T. Yap ◽

Vytas Reipa

Keyword(s):

Electron Transfer ◽

Electrode Surface ◽

Gold Electrode ◽

Direct Electron Transfer

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The Development of a Direct Electron Transfer Type Open Circuit Potential Based Glucose Sensor Utilizing Microneedle Type Gold Electrode

ECS Meeting Abstracts ◽

10.1149/ma2019-01/45/2227 ◽

2019 ◽

Keyword(s):

Electron Transfer ◽

Gold Electrode ◽

Open Circuit Potential ◽

Glucose Sensor ◽

Direct Electron Transfer ◽

Open Circuit

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Direct electron transfer of horseradish peroxidase on Nafion-cysteine modified gold electrode

Electrochimica Acta ◽

10.1016/j.electacta.2007.04.024 ◽

2007 ◽

Vol 52 (21) ◽

pp. 6261-6267 ◽

Cited By ~ 55

Author(s):

Jun Hong ◽

Ali Akbar Moosavi-Movahedi ◽

Hedayatollah Ghourchian ◽

Ahmad Molaei Rad ◽

Saeed Rezaei-Zarchi

Keyword(s):

Electron Transfer ◽

Horseradish Peroxidase ◽

Gold Electrode ◽

Direct Electron Transfer

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Promoter effect of poly(4-vinylpyridine) on the direct electron transfer between cytochrome c and gold electrode

Journal of Molecular Catalysis A Chemical ◽

10.1016/1381-1169(95)90046-2 ◽

1995 ◽

Vol 102 (2) ◽

pp. 111-116 ◽

Cited By ~ 12

Author(s):

Xiaogang Qu ◽

Tianhong Lu ◽

Shaojun Dong

Keyword(s):

Electron Transfer ◽

Cytochrome C ◽

Gold Electrode ◽

Direct Electron Transfer ◽

Promoter Effect

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Refining the reaction mechanism of O2 towards its substrate in cofactor-free dioxygenases

10.7287/peerj.preprints.2145v1 ◽

2016 ◽

Author(s):

Pedro J Silva

Keyword(s):

Electron Transfer ◽

Active Site ◽

Quantum Chemical ◽

Potential Energy Surfaces ◽

Direct Electron Transfer ◽

Minimum Energy ◽

Urate Oxidase ◽

Redox Potentials ◽

Deprotonated Form ◽

Quantum Chemical Computations

Cofactor-less oxygenases perform challenging catalytic reactions between singlet substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In bacterial ring-cleaving 2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from substrate to O2 followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far.

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Geobacter sulfurreducens inner membrane cytochrome CbcBA controls electron transfer and growth yield near the energetic limit of respiration

10.1101/2021.04.15.440034 ◽

2021 ◽

Author(s):

Komal Joshi ◽

Chi Ho Chan ◽

Daniel R. Bond

Keyword(s):

Electron Transfer ◽

Redox Potential ◽

Growth Yield ◽

Growth Efficiency ◽

Geobacter Sulfurreducens ◽

Redox Potentials ◽

Hydrogen Electrode ◽

Highly Expressed Genes ◽

Reducing Bacteria ◽

Transfer Chain

AbstractGeobacter sulfurreducens utilizes extracellular electron acceptors such as Mn(IV), Fe(III), syntrophic partners, and electrodes that vary from +0.4 to −0.3 V vs. Standard Hydrogen Electrode (SHE), representing a potential energy span that should require a highly branched electron transfer chain. Here we describe CbcBA, a bc-type cytochrome essential near the thermodynamic limit of respiration when acetate is the electron donor. Mutants lacking cbcBA ceased Fe(III) reduction at −0.21 V vs. SHE, could not transfer electrons to electrodes between −0.21 and −0.28 V, and could not reduce the final 10% – 35% of Fe(III) minerals. As redox potential decreased during Fe(III) reduction, cbcBA was induced with the aid of the regulator BccR to become one of the most highly expressed genes in G. sulfurreducens. Growth yield (CFU/mM Fe(II)) was 112% of WT in ΔcbcBA, and deletion of cbcL (a different bc-cytochrome essential near −0.15 V) in ΔcbcBA increased yield to 220%. Together with ImcH, which is required at high redox potentials, CbcBA represents a third cytoplasmic membrane oxidoreductase in G. sulfurreducens. This expanding list shows how these important metal-reducing bacteria may constantly sense redox potential to adjust growth efficiency in changing environments.

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Redox potential as a master variable controlling pathways of metal reduction byGeobacter sulfurreducens

10.1101/043059 ◽

2016 ◽

Cited By ~ 1

Author(s):

Caleb E. Levar ◽

Colleen L. Hoffman ◽

Aubrey J. Dunshee ◽

Brandy M. Toner ◽

Daniel R. Bond

Keyword(s):

Redox Potential ◽

Geobacter Sulfurreducens ◽

High Potential ◽

Growth Yields ◽

Redox Potentials ◽

Hydrogen Electrode ◽

Additional Energy ◽

Single Organism ◽

Wide Range ◽

Dependent Pathway

AbstractGeobacter sulfurreducensuses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of −0.10 V vs. the Standard Hydrogen Electrode (SHE), while the ImcH-dependent pathway operates only above this value. Here, we provide evidence thatG. sulfurreducensalso requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)- (oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment.

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