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Electron Transport Chain: Complex I and II

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The mitochondrial electron transport chain (ETC) is the main energy generation system in the eukaryotic cells. However, mitochondria also produce cytotoxic reactive oxygen species (ROS) due to the large electron flow during oxidative phosphorylation. While Complex I is one of the primary sources of superoxide radicals, ROS production by Complex II is uncommon and may only be observed in cancer cells with mutated complexes.
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Related Experiment Video

Updated: Jun 11, 2026

Analyzing Supercomplexes of the Mitochondrial Electron Transport Chain with Native Electrophoresis, In-gel Assays, and Electroelution

Analyzing Supercomplexes of the Mitochondrial Electron Transport Chain with Native Electrophoresis, In-gel Assays, and Electroelution

Published on: June 1, 2017

Functional modules and structural basis of conformational coupling in mitochondrial complex I.

Carola Hunte¹, Volker Zickermann, Ulrich Brandt

¹Institute for Biochemistry and Molecular Biology, Centre for Biological Signalling Studies (BIOSS), University of Freiburg, D-79104 Freiburg, Germany.

Science (New York, N.Y.)

|July 3, 2010

Summary

Researchers mapped mitochondrial complex I using X-ray crystallography, revealing the ubiquinone reduction site and a helical element crucial for energy transduction in cellular respiration and preventing neurodegenerative diseases.

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Area of Science:

Biochemistry
Structural Biology
Cellular Respiration

Background:

Proton-pumping respiratory complex I is a large, intricate membrane protein essential for cellular energy production.
Complex I dysfunction is linked to various neurodegenerative disorders, highlighting its clinical significance.

Purpose of the Study:

To elucidate the high-resolution structure of mitochondrial complex I using X-ray crystallography.
To determine the precise locations of iron-sulfur clusters and the ubiquinone reduction site within the complex.
To understand the mechanism of proton pumping and energy transduction.

Main Methods:

X-ray crystallography of the complete mitochondrial complex I enzyme.
Analysis of the spatial arrangement of functional modules and iron-sulfur clusters.

Main Results:

The precise positions of all iron-sulfur clusters relative to the membrane arm were determined.
The ubiquinone reduction site was localized approximately 30 angstroms above the membrane domain.
A ~60-angstrom helical transmission element was identified as critical for energy transduction.

Conclusions:

The structural data suggest conformational coupling between redox chemistry and proton pumping, excluding direct mechanisms.
The identified helical element likely plays a key role in transmitting conformational energy for proton pumping.
Understanding complex I structure is vital for insights into cellular energy metabolism and neurodegenerative diseases.