Respiratory complex I: A dual relation with H(+) and Na(+)?

Area of Science:

• Biochemistry
• Molecular Biology
• Bioenergetics

Background:

• Respiratory complex I links NADH:quinone oxidoreduction to ion translocation, establishing electrochemical potential.
• While protons (H+) are the recognized coupling ions, some evidence suggests sodium ions (Na+) may also play a role.
• Previous observations indicated NADH-driven Na+ transport in menaquinone-reducing complexes I, suggesting Na+/H+ antiporter activity.

Purpose of the Study:

• To investigate the potential role of Na+/H+ antiporter activity in respiratory complex I.
• To explore the hypothesis that menaquinone-reducing complexes I employ Na+/H+ antiporter activity to achieve a specific stoichiometry.
• To understand the broader physiological implications of complex I function beyond simple redox coupling.

Main Methods:

• Comparative analysis of menaquinone- and ubiquinone-reducing complexes I.
• Observation of NADH-driven ion transport.
• Structural homology analysis of complex I subunits with known Na+/H+ antiporters.

Main Results:

• Menaquinone-reducing complexes I exhibited NADH-driven Na+ transport opposite to H+ translocation, indicating Na+/H+ antiporter activity.
• Ubiquinone-reducing mitochondrial complex I also showed Na+/H+ antiporter activity in its deactive form.
• Less energy is available for ion translocation in menaquinone-reducing complexes I compared to ubiquinone-reducing ones.

Conclusions:

• The Na+/H+ antiporter activity in menaquinone-reducing complexes I may be crucial for achieving the 4H+/2e- stoichiometry.
• Ubiquinone-utilizing organisms might retain Na+/H+ antiporter activity under specific conditions.
• Complex I likely possesses sophisticated physiological roles beyond basic redox coupling and ion transport.