Connecting CuA with metal centers of heme a, heme a, CuB and Zn by pathways with hydrogen bond as the bridging element in cytochrome c oxidase.

Pathways formed of delocalized π-electron systems and polar groups of polypeptide chains bridged by hydrogen bonds are referred as π-H pathways. Suitable for electron transfer, these pathways in cytochrome c oxidase connect CuA, the source of electrons distributed in cytochrome c oxidase, with the metal centers, heme a, heme a, CuB, the constituents of the catalytic binuclear center. The unusually rapid electron transfer between heme a and heme a would have been facilitated by the link pathway of a long sequence of alternate peptide unit and hydrogen bond spanning Pro336-Val374, referred as suprahelix, between these hemes. Two pathways between CuA center and zinc center, share some portions with purported proton-translocating channels, designated "K" and "D".