C-type cytochrome. Part of the cbb3-type cytochrome c oxidase complex. CcoP subunit is required for transferring electrons from donor cytochrome c via its heme groups to CcoO subunit. From there, electrons are shuttled to the catalytic binuclear center of CcoN subunit where oxygen reduction takes place. The complex also functions as a proton pump. Binds 2 heme C groups per subunit. Energy metabolism; oxidative phosphorylation. Component of the cbb3-type cytochrome c oxidase at least composed of CcoN, CcoO, CcoQ and CcoP. Single ccoP mutant as well as ccoP rdxB double mutant give rise to colonies with very deep red pigmentation compared to wild-type when grown on SIS agar plates in the presence of O(2). The same mutants don't have cytochrome c oxidase activity and they accumulate high levels of a yellow carotenoid spheroidenone (SO) during anoxygenic photosynthetic and diazotrophic growth. Expression of crtA in the ccoP rdxB double mutant is approximately 60% higher than that observed for wild-type. Disruption of crtA together with ccoP and rdxB mutants prevent the accumulation of SO. CcoP and rdxB mutants, either singly or in combination, are found to synthesize photosynthetic complexes compared with wild-type when grown in the presence of 30% oxygen. They show a greater than 10-fold increase in levels of transcription of genes encoding photosynthetic light-harvesting complexes compared to the levels with wild-type. CcoP single mutant shows increased levels of photopigments bacteriochlorophyll and carotenoid under aerobic conditions. It produces more light-harvesting complexes and photopigments under photosynthetic conditions than under anaerobic dark conditions. It has no cytochrome c oxidase activity under anaerobic dark conditions. Addition of dimethyl sulfoxide (DMSO) to photosynthetic cultures of the ccoP mutant leads to decreased levels of photosynthetic light-harvesting complexes. Belongs to the CcoP / FixP family.