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Energy-dependent Complex I-associated ubisemiquinones in submitochondrial particles
A D Vinogradov1, V D Sled, D S Burbaev
1Department of Biochemistry, School of Biology, Moscow State University, Russian Federation.
FEBS Letters
|August 14, 1995
Summary
Researchers identified two ubisemiquinone species in Complex I using cryogenic EPR. These findings reveal their spatial arrangement and role in proton translocation during cellular respiration.
Area of Science:
- Biochemistry
- Molecular Biology
- Bioenergetics
Background:
- Mitochondrial Complex I is crucial for cellular respiration.
- Ubisemiquinones are key intermediates in electron transfer.
- Understanding their precise roles requires detailed structural and dynamic information.
Purpose of the Study:
- To characterize the distinct ubisemiquinone species associated with Complex I.
- To elucidate the spatial relationship between ubisemiquinones and iron-sulfur clusters.
- To investigate the role of ubisemiquinones in proton translocation.
Main Methods:
- Cryogenic Electron Paramagnetic Resonance (EPR) spectroscopy.
- Analysis of tightly coupled submitochondrial particles oxidizing NADH or succinate.
- Steady-state kinetic measurements and temperature-dependent signal analysis.
Main Results:
- Detection of two distinct ubisemiquinone species: fast-relaxing (SQNf) and slow-relaxing (SQNs).
- Sensitivity of both species to uncouplers, rotenone, and Complex I deactivation.
- Determination of the distance between SQNf and the N2 iron-sulfur cluster (8-11 Å) via spin-spin interactions.
Conclusions:
- A model is proposed where N2 and two interacting ubisemiquinone species are spatially arranged in Complex I's hydrophobic domain.
- These ubisemiquinone species are directly involved in vectorial proton translocation.
- Cryogenic EPR provides critical insights into the mechanism of Complex I.