X‐ray Crystal Structures of Cytochrome c Oxidases from Paracoccus denitrificans and Bovine Heart and Their Implications for the Molecular Mechanism of Cell Respiration

Pores with rotational symmetry, each formed from five transmembrane helices in cytochrome c oxidase, form the postulated pathways for the protons required for the biochemical reduction of O2 as well as for the protons transported across the cell (or inner mitochondrial) membrane resulting in a H+ gradient. The structures of cytochrome c oxidase from a bacterium recently described by Michel et al. and from bovine heart by Yoshikawa et al. corroborate many previous results on the structure and function of this enzyme and disprove others.