When the excited chlorophyll P passes the electron to pheophytin, it converts to high-energy P, which can oxidize the tyrosine (or Y) molecule by ripping off one of its hydrogen atoms. The high-energy oxidized tyrosine gives off its energy and returns to the ground state by taking up a proton and removing an electron from the oxygen-evolving complex and ultimately from water. Kok's S-state diagram shows the reactions of water splitting in the oxygen-evolving complex.