electrochemical-detection-deuterium-kinetic-isotope-effect-on

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in <em>Shewanella oneidensis</em> MR-1

Direct electrochemical detection of c-type cytochrome complexes embedded in the bacterial outer membrane (outer membrane c-type cytochrome complexes; OM ...

University of Tokyo

Outer-membrane -type cytochrome (OM Cyt) complexes in several genera of iron-reducing bacteria, such as  and , are capable of transporting electrons from the cell interior to extracellular solids as a terminal step of anaerobic respiration. The kinetics of this electron transport has implications for controlling the rate of microbial electron transport during bioenergy or biochemical production, iron corrosion, and natural mineral cycling. Herein, we review the findings from  and  studies examining electron transport kinetics through single OM Cyt complexes in  MR-1.  electron flux via a purified OM -Cyt complex, comprised of MtrA, B, and C proteins from  MR-1, embedded in a proteoliposome system is reported to be 10- to 100-fold faster compared with  estimates based on measurements of electron flux per cell and OM -Cyts density. As the proteoliposome system is estimated to have 10-fold higher cation flux via potassium channels than electrons, we speculate that the slower rate of electron-coupled cation transport across the OM is responsible for the significantly lower electron transport rate that is observed . As most studies to date have primarily focused on the energetics or kinetics of interheme electron hopping in OM -Cyts in this microbial electron transport mechanism, the proposed model involving cation transport provides new insight into the rate detemining step of EET, as well as the role of self-secreted flavin molecules bound to OM -Cyt and proton management for energy conservation and production in  MR-1.

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

The microbial transfer of electrons to extracellularly located solid compounds, termed extracellular electron transport (EET), is critical for microbial electrode catalysis. Although the components of the EET pathway in the outer membrane (OM) have been identified, the role of electron/cation coupling in EET kinetics is poorly understood. We studied the dynamics of proton transport associated with EET in an OM flavocytochrome complex in Shewanella oneidensis MR-1. Using a whole-cell electrochemical assay, a significant kinetic isotope effect (KIE) was observed following the addition of deuterated water (D O). The removal of a flavin cofactor or key components of the OM flavocytochrome complex significantly increased the KIE in the presence of D O to values that were significantly larger than those reported for proton channels and ATP synthase, thus indicating that proton transport by OM flavocytochrome complexes limits the rate of EET.

Article	Year
Cation-limited kinetic model for microbial extracellular electron transport via an outer membrane cytochrome complex. Biophysics and physicobiology\| PubMed ID: 27924259	2016
Proton Transport in the Outer-Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport. Angewandte Chemie (International ed. in English)\| PubMed ID: 28608645	2017

Yoshihide Tokunou

Biography

JoVE Journal Publications

Other Publications