Function
Low-potential cytochrome c that plays a role in the oxygen-evolving complex of photosystem II (PSII). Binds to PSII in the absence of other extrinsic proteins; required for binding of the PsbU protein to photosystem II. In PSII particles without oxygen-evolving activity, maximal activity is restored only by binding of cytochrome c550, PsbU and the 33 kDa PsbO protein. PSII is a light-driven water plastoquinone oxidoreductase, using light energy to abstract electrons from H(2)O, generating a proton gradient subsequently used for ATP formation.