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Electron Transport Chains

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The final stage of cellular respiration is oxidative phosphorylation that consists of two steps: the electron transport chain and chemiosmosis. The electron transport chain is a set of proteins found in the inner mitochondrial membrane in eukaryotic cells. Its primary function is to establish a proton gradient that can be used during chemiosmosis to produce ATP and generate electron carriers, such as NAD+ and FAD, that are used in glycolysis and the citric acid cycle.
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During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...

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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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Role of Reduced Coenzymes NADH and FADH₂

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The energy released from the breakdown of the chemical bonds within nutrients can be stored either through the reduction of electron carriers or in the bonds of adenosine triphosphate (ATP). In living systems, a small class of compounds functions as mobile electron carriers, molecules that bind to and shuttle high-energy electrons between compounds in pathways. The principal electron carriers that will be considered originate from the B vitamin group and are derivatives of nucleotides; they are...

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The electron transport chain (ETC) is a crucial metabolic pathway that facilitates energy conversion in prokaryotic and eukaryotic cells. In eukaryotes, the ETC comprises four membrane-associated protein complexes in the inner mitochondrial membrane. In prokaryotes, the ETC in the plasma membrane can vary in composition, with fewer or different complexes depending on the organism and environmental conditions. These complexes transfer electrons from electron donors, such as NADH and FADH2, to...

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Related Experiment Video

Updated: Jul 11, 2026

Determination of Tripartite Interaction between Two Monomers of a MADS-box Transcription Factor and a Calcium Sensor Protein by BiFC-FRET-FLIM Assay

Determination of Tripartite Interaction between Two Monomers of a MADS-box Transcription Factor and a Calcium Sensor Protein by BiFC-FRET-FLIM Assay

Published on: December 25, 2021

Obligatory intermolecular electron-transfer from FAD to FMN in dimeric P450BM-3.

Tatsuya Kitazume¹, Donovan C Haines, Ronald W Estabrook

¹Department of Biochemistry, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9038, USA.

|October 2, 2007

Summary

The enzyme P450BM-3 dimerizes to become active, with electron transfer occurring between molecules in the dimer. This dimerization is crucial for its catalytic function in monooxygenation reactions.

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Extraction of Cofactor F420 for Analysis of Polyglutamate Tail Length from Methanogenic Pure Cultures and Environmental Samples

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Published on: October 14, 2021

Area of Science:

Biochemistry
Enzymology
Protein Dynamics

Background:

Cytochromes P450 catalyze essential monooxygenation reactions.
P450BM-3 is a P450 enzyme fused with a reductase domain.
Previous studies noted nonlinear kinetics for P450BM-3.

Purpose of the Study:

Investigate the cause of P450BM-3 inactivation upon dilution.
Determine the active form of P450BM-3.
Elucidate the electron transfer pathway in P450BM-3.

Main Methods:

Enzyme kinetics assays
Cross-linking experiments
Molecular weight determination
Site-directed mutagenesis

Main Results:

P450BM-3 dimerizes in solution, and the dimer is the catalytically active form.
Substrate presence reduces enzyme inactivation upon dilution.
Electron transfer occurs between reductase domains of different P450BM-3 monomers in the dimer.

Conclusions:

P450BM-3 functions as a dimer for significant catalytic activity.
The electron transfer pathway involves inter-molecular transfer between FAD and FMN domains.
This inter-subunit electron transfer is essential for P450BM-3's monooxygenation function.