Electrons from water do not pass directly to P680
Oxygen evolving complex ( OEC ) or water splitting complex ( WSC )
Tyr residue of D protein participates in OEC.
4 P680+ + 4 Tyr ---- 4 P680 + 4Tyr·
Tyr· radical abstracts 4 electrons in sequence from [ Mn Complex ] 0 and oxidizes it to [ Mn Complex ]+4
4Tyr· + [ Mn Complex ]0 ---- 4 Tyr + [ Mn Complex ]+4
[ Mn Complex ]+4 accepts 4 e from water at a time .
[ Mn Complex ]+4 + 2H2O ---- [ Mn Complex ]0 + 4 H+ + O2
OEC acts as a proton pump driven by electron transfer.
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