ΔμH+Dependency of Proton Translocation by Bacteriorhodopsin and a Stochastic Energization−Relaxation Channel Model

1996 ◽  
Vol 100 (50) ◽  
pp. 19687-19691 ◽  
Author(s):  
Eiro Muneyuki ◽  
Mineo Ikematsu ◽  
Masasuke Yoshida
Keyword(s):  
Channel Model ◽  
Proton Translocation ◽  
Relaxation Channel

scholarly journals Oversized ubiquinones as molecular probes for structural dynamics of the ubiquinone reaction site in mitochondrial respiratory complex I

2020 ◽  
Vol 295 (8) ◽  
pp. 2449-2463 ◽  
Author(s):  
Shinpei Uno ◽  
Takahiro Masuya ◽  
Kyoko Shinzawa-Itoh ◽  
Jonathan Lasham ◽  
Outi Haapanen ◽  
...  
Keyword(s):  
Complex I ◽  
Channel Model ◽  
Proton Translocation ◽  
Molecular Probes ◽  
Side Chain ◽  
Reaction Site ◽  
Quinone Oxidoreductase ◽  
Access Path ◽  
Quinone Reduction ◽  
Access Channel

NADH-quinone oxidoreductase (complex I) couples electron transfer from NADH to quinone with proton translocation across the membrane. Quinone reduction is a key step for energy transmission from the site of quinone reduction to the remotely located proton-pumping machinery of the enzyme. Although structural biology studies have proposed the existence of a long and narrow quinone-access channel, the physiological relevance of this channel remains debatable. We investigated here whether complex I in bovine heart submitochondrial particles (SMPs) can catalytically reduce a series of oversized ubiquinones (OS-UQs), which are highly unlikely to transit the narrow channel because their side chain includes a bulky “block” that is ∼13 Å across. We found that some OS-UQs function as efficient electron acceptors from complex I, accepting electrons with an efficiency comparable with ubiquinone-2. The catalytic reduction and proton translocation coupled with this reduction were completely inhibited by different quinone-site inhibitors, indicating that the reduction of OS-UQs takes place at the physiological reaction site for ubiquinone. Notably, the proton-translocating efficiencies of OS-UQs significantly varied depending on their side-chain structures, suggesting that the reaction characteristics of OS-UQs affect the predicted structural changes of the quinone reaction site required for triggering proton translocation. These results are difficult to reconcile with the current channel model; rather, the access path for ubiquinone may be open to allow OS-UQs to access the reaction site. Nevertheless, contrary to the observations in SMPs, OS-UQs were not catalytically reduced by isolated complex I reconstituted into liposomes. We discuss possible reasons for these contradictory results.

A Markov-Based Satellite-to-Ground Optical Channel Model and Its Effective Coding Scheme

2012 ◽  
Vol E95-B (1) ◽  
pp. 254-262
Author(s):  
Yoshitoshi YAMASHITA ◽  
Eiji OKAMOTO ◽  
Yasunori IWANAMI ◽  
Yozo SHOJI ◽  
Morio TOYOSHIMA ◽  
...  
Keyword(s):  
Channel Model ◽  
Optical Channel ◽  
Coding Scheme
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