Energy transduction: proton transfer through the respiratory complexes.

Area of Science:

• Biochemistry and Biophysics
• Membrane Protein Function
• Bioenergetics

Background:

• Metalloprotein complexes embedded in mitochondrial and bacterial membranes are crucial for energy generation.
• These complexes utilize electron transfer reactions to establish an electrochemical proton gradient (DeltamuH+).
• Understanding electron-driven proton transfer is key to comprehending cellular respiration and energy transduction.

Purpose of the Study:

• To review the current understanding of electron-driven proton transfer mechanisms in metalloprotein complexes.
• To highlight key structural and experimental evidence supporting proton pumping models.
• To identify remaining questions regarding gating mechanisms and physiological control.

Main Methods:

• Review of structural, experimental, and theoretical studies on metalloprotein complexes, particularly cytochrome c oxidase.
• Analysis of models for long-distance proton transfer via hydrogen-bonded water chains.
• Examination of evidence for the roles of specific amino acid residues and bound water molecules.

Main Results:

• Structural and experimental data support proton pumping models involving hydrogen-bonded water chains.
• Proton uptake and release are linked to charge changes at membrane-embedded redox centers.
• Bound water, carboxylates, heme propionates, and arginines are implicated in the pumping mechanism.

Conclusions:

• The fundamental principles of electron-driven proton pumping are supported by significant evidence.
• The precise roles of subunit III and proton backflow require further investigation.
• The mechanisms governing gating and physiological control of proton pump efficiency remain largely unknown.