C-type cytochrome. Part of the cbb3-type cytochrome c oxidase complex. FixP subunit is required for transferring electrons from donor cytochrome c via its heme groups to FixO subunit. From there, electrons are shuttled to the catalytic binuclear center of FixN subunit where oxygen reduction takes place. The complex also functions as a proton pump (By similarity). Binds 2 heme C groups per subunit. Energy metabolism; oxidative phosphorylation. Component of the cbb3-type cytochrome c oxidase at least composed of FixN, FixO, FixQ and FixP. Belongs to the CcoP / FixP family.