Dec 16, 2003

The low-spin heme of cytochrome c oxidase as the driving element of the proton-pumping process

Proceedings of the National Academy of Sciences of the United States of America
Tomitake TsukiharaShinya Yoshikawa

Abstract

Mitochondrial cytochrome c oxidase plays an essential role in aerobic cellular respiration, reducing dioxygen to water in a process coupled with the pumping of protons across the mitochondrial inner membrane. An aspartate residue, Asp-51, located near the enzyme surface, undergoes a redox-coupled x-ray structural change, which is suggestive of a role for this residue in redox-driven proton pumping. However, functional or mechanistic evidence for the involvement of this residue in proton pumping has not yet been obtained. We report that the Asp-51 --> Asn mutation of the bovine enzyme abolishes its proton-pumping function without impairment of the dioxygen reduction activity. Improved x-ray structures (at 1.8/1.9-A resolution in the fully oxidized/reduced states) show that the net positive charge created upon oxidation of the low-spin heme of the enzyme drives the active proton transport from the interior of the mitochondria to Asp-51 across the enzyme via a water channel and a hydrogen-bond network, located in tandem, and that the enzyme reduction induces proton ejection from the aspartate to the mitochondrial exterior. A peptide bond in the hydrogen-bond network critically inhibits reverse proton transfer through the network. ...Continue Reading

  • References18
  • Citations197

Mentioned in this Paper

Cytochrome C Oxidase
Cytochrome c Oxidase Subunit VIa
Aspartic Acid, Magnesium-Potassium (2:1:2) Salt
Aspartate
Plain X-ray
Cell Respiration
Bos taurus
Mitochondria, Heart
Protons
Oxidation

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