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. Binds 1 heme c group covalently per subunit. PSII binds multiple chlorophylls, carotenoids and specific lipids. The cyanobacterial oxygen-evolving complex is composed of PsbO, PsbP, PsbQ, PsbV and PsbU (Probable). PsbP and PsbQ are not seen in the crystal structures; however there is biochemical evidence that they are part of the OEC. Cyanobacterial PSII is composed of 1 copy each of membrane proteins PsbA, PsbB, PsbC, PsbD, PsbE, PsbF, PsbH, PsbI, PsbJ, PsbK, PsbL, PsbM, PsbT, PsbX, PsbY, PsbZ, Ycf12, 3 peripheral proteins PsbO, PsbU, PsbV and a large number of cofactors. It forms dimeric complexes. Associated with photosystem II at the lumenal side of the thylakoid membrane. Belongs to the cytochrome c family. PsbV subfamily.