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Related Concept Videos

ATP Synthase: Mechanism01:48

ATP Synthase: Mechanism

In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased ATP...
Electron Transport Chain: Complex III and IV01:43

Electron Transport Chain: Complex III and IV

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...
Chemiosmosis01:32

Chemiosmosis

Oxidative phosphorylation is a highly efficient process that generates large amounts of adenosine triphosphate (ATP), the basic unit of energy that drives many cellular processes. Oxidative phosphorylation involves two processes— the electron transport chain and chemiosmosis.
Electron Transport Chain
The electron transport chain involves a series of protein complexes on the inner mitochondrial membrane that undergo a series of redox reactions. At the end of this chain, the electrons reduce...
ATP Synthase: Structure01:18

ATP Synthase: Structure

ATP synthase or ATPase is among the most conserved proteins found in bacteria, mammals, and plants. This enzyme can catalyze a forward reaction in response to the electrochemical gradient, producing ATP from ADP and inorganic phosphate. ATP synthase can also work in a reverse direction by hydrolyzing ATP and generating an electrochemical gradient. Different forms of ATP synthases have evolved special features to meet the specific demands of the cell. Based on their specific feature, ATP...
ATP Driven Pumps II: P-type Pumps01:34

ATP Driven Pumps II: P-type Pumps

The P-type pumps are a large family of integral membrane transporter ATPases. They are divided into five major types based on substrate specificity, from I to V.
A typical P-type pump has three cytosolic domains: nucleotide-binding (N), phosphorylation (P), and activator (A) domains. These domains are connected to the membrane-spanning helices by short amino acid segments. ATP hydrolysis and covalent phosphoenzyme intermediate formation are crucial parts of the catalytic cycle. At the highly...
ATP Driven Pumps I: An Overview01:27

ATP Driven Pumps I: An Overview

ATP-driven pumps, also known as transport ATPases, are integral membrane proteins. They have binding sites for ATP located on the membrane's cytosolic side and the ion-conducting domain in the transmembrane region. These pumps use the free energy released from ATP hydrolysis to move the solutes across cell membranes against an electrochemical gradient.
There are four main types of ATP-driven pumps - P-type, V-type, F-type, and ABC transporter. All these pumps are of varying complexities and are...

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Related Experiment Video

Updated: Jun 2, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method
05:51

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

Published on: July 19, 2019

A two-state stabilization-change mechanism for proton-pumping complex I.

Ulrich Brandt1

  • 1Center for Membrane Proteomics, Goethe-University, Frankfurt am Main, Germany. brandt@zbc.kgu.de

Biochimica Et Biophysica Acta
|May 14, 2011
PubMed
Summary
This summary is machine-generated.

A new mechanism explains how respiratory complex I pumps protons during oxidative phosphorylation. It involves conformational changes driven by ubiquinone reduction, explaining the 4 H+/2e- stoichiometry and reversible function.

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Last Updated: Jun 2, 2026

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Published on: July 19, 2019

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • The molecular mechanism of proton pumping by respiratory complex I remains largely unknown.
  • Recent X-ray crystallographic studies of complex I have revealed crucial details about its molecular architecture.

Purpose of the Study:

  • To propose a hypothetical molecular mechanism for the redox-driven proton pumping activity of respiratory complex I.
  • To explain the experimentally determined proton pumping stoichiometry and reversible function of complex I.

Main Methods:

  • Hypothetical mechanism based on recent X-ray crystallographic data of complex I.
  • Two-state model involving stabilization of anionic semiquinone and ubiquinol forms.
  • Conformational energy transfer through a helical transmission element.

Main Results:

  • A mechanism where two pump modules are driven by conformational strokes linked to ubiquinone reduction states.
  • Explains the observed stoichiometry of 4 H+/2e-.
  • The proposed mechanism is fully reversible, explaining forward and reverse modes of complex I function.

Conclusions:

  • The proposed two-state stabilization-change mechanism provides a cohesive explanation for respiratory complex I proton pumping.
  • This model integrates structural insights with functional observations of complex I activity.