scholarly journals Cation-limited kinetic model for microbial extracellular electron transport via an outer membrane cytochrome C complex

2016 ◽  
Vol 13 (0) ◽  
pp. 71-76 ◽  
Author(s):  
Akihiro Okamoto ◽  
Yoshihide Tokunou ◽  
Junki Saito
Keyword(s):  
Electron Transport ◽  
Kinetic Model ◽  
Outer Membrane ◽  
Extracellular Electron Transport

scholarly journals Basicity of N5 in semiquinone enhances the rate of respiratory electron outflow inShewanella oneidensisMR-1

2019 ◽  
Author(s):  
Yoshihide Tokunou ◽  
Keisuke Saito ◽  
Ryo Hasegawa ◽  
Kenneth H. Nealson ◽  
Kazuhito Hashimoto ◽  
...  
Keyword(s):  
Free Energy ◽  
Electron Transport ◽  
Nitrogen Atom ◽  
Outer Membrane ◽  
Diffusion Constant ◽  
Shewanella Oneidensis ◽  
Molecular Structures ◽  
Redox Potentials ◽  
Transport Reaction ◽  
Extracellular Electron Transport

AbstractExtracellular electron transport (EET) occurs in environmental iron-reducing bacteria and is mediated by an outer membrane multi-heme cytochrome complex (Cyts). It has critical implications for global mineral cycling and electrochemical microbial catalysis. The rate of EET mediated by multiple heme redox centers significantly increases in the presence of flavins and quinones. Their electron free energy does not entirely account for the fact that differential effects on EET rate enhancement vary significantly by factors ≥100. Here, we report on whole-cell electrochemical analysis ofShewanella oneidensisMR-1 using six flavin analogs and four quinones. We demonstrated that protonation of the nitrogen atom at position 5 (N5) of the isoalloxazine ring is essential for electron outflow acceleration as a bound non-covalent cofactor of Cyts. EET mediated by Cyts was accelerated at a rate dependent on pKa(N5). The EET rate largely decreased in response to the addition of deuterated water (D2O), while low concentration of D2O (4 %) had little impact on electron free energy difference of the heme and non-covalent bound cofactors, strongly suggesting that the protonation of N5 limits the rate of EET. Our findings directly link EET kinetics to proton transport reaction via N5 and provide a basis for the development of novel strategies for controlling EET-associated biological reactions.Significance statementThe potential of various small molecules such as flavins and quinones to enhance the rate of extracellular electron transport (EET) has been exploited to develop environmental energy conversion systems. Flavins and quinones have similar molecular structures but their abilities to enhance EET vary by >100× inShewanella oneidensisMR-1. These large differences are inconsistent with conventional models, which rely on redox potentials or diffusion constant of shuttling electron mediators. In this study, we demonstrated that the basicity of the nitrogen atom of the isoalloxazine ring (N5) enhances the rate of electron outflow when a flavin or quinone is a non-covalent cofactor ofS. oneidensisMR-1 outer membranec-type cytochromes.

scholarly journals Proton Transport in the Outer-Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport

2017 ◽  
Vol 56 (31) ◽  
pp. 9082-9086 ◽  
Author(s):  
Akihiro Okamoto ◽  
Yoshihide Tokunou ◽  
Shafeer Kalathil ◽  
Kazuhito Hashimoto
Keyword(s):  
Electron Transport ◽  
Outer Membrane ◽  
Proton Transport ◽  
Extracellular Electron Transport

scholarly journals Bacterial Nanowires of Shewanella Oneidensis MR-1 are Outer Membrane and Periplasmic Extensions of the Extracellular Electron Transport Components

2015 ◽  
Vol 108 (2) ◽  
pp. 368a ◽  
Author(s):  
Sahand Pirbadian ◽  
Sarah E. Barchinger ◽  
Kar Man Leung ◽  
Hye Suk Byun ◽  
Yamini Jangir ◽  
...  
Keyword(s):  
Electron Transport ◽  
Outer Membrane ◽  
Shewanella Oneidensis ◽  
Extracellular Electron Transport ◽  
Bacterial Nanowires

scholarly journals Proton Transport in the Outer-Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport

2017 ◽  
Vol 129 (31) ◽  
pp. 9210-9214 ◽  
Author(s):  
Akihiro Okamoto ◽  
Yoshihide Tokunou ◽  
Shafeer Kalathil ◽  
Kazuhito Hashimoto
Keyword(s):  
Electron Transport ◽  
Outer Membrane ◽  
Proton Transport ◽  
Extracellular Electron Transport

Pulmonary reduction of an intravascular redox polymer

2001 ◽  
Vol 280 (6) ◽  
pp. L1290-L1299 ◽  
Author(s):  
Said H. Audi ◽  
Robert D. Bongard ◽  
Yoshiyuki Okamoto ◽  
Marilyn P. Merker ◽  
David L. Roerig ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Superoxide Dismutase ◽  
Electron Transport ◽  
Kinetic Model ◽  
Electron Acceptors ◽  
Redox Polymer ◽  
Pulmonary Endothelial Cells ◽  
Equilibrium Level ◽  
A Cell

Pulmonary endothelial cells in culture reduce external electron acceptors via transplasma membrane electron transport (TPMET). In studying endothelial TPMET in intact lungs, it is difficult to exclude intracellular reduction and reducing agents released by the lung. Therefore, we evaluated the role of endothelial TPMET in the reduction of a cell-impermeant redox polymer, toluidine blue O polyacrylamide (TBOP+), in intact rat lungs. When added to the perfusate recirculating through the lungs, the venous effluent TBOP+concentration decreased to an equilibrium level reflecting TBOP+ reduction and autooxidation of its reduced (TBOPH) form. Adding superoxide dismutase (SOD) to the perfusate increased the equilibrium TBOP+ concentration. Kinetic analysis indicated that the SOD effect could be attributed to elimination of the superoxide product of TBOPH autooxidation rather than of superoxide released by the lungs, and experiments with lung-conditioned perfusate excluded release of other TBOP+ reductants in sufficient quantities to cause significant TBOP+ reduction. Thus the results indicate that TBOP+ reduction is via TPMET and support the utility of TBOP+ and the kinetic model for investigating TPMET mechanisms and their adaptations to physiological and pathophysiological stresses in the intact lung.

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