Abstract
The local environment of the manganese cluster in photosystem II has been investigated using proton matrix ENDOR. Six pairs of proton ENDOR signals were detected in multiline signals in both the S0 and the S2. The 6 pair of lines separated around the position for a free proton was detected. The signals with 2.2-2.3 MHz hyperfine constants disappeared within 3 h of D2O exchange in both the S0 and S2 states. However, the signals with 4.0 MHz hyperfine constants disappeared within 3 and 24 hours in the S0 and S2 states, respectively. The different rates were ascribed to oxidation of the liganding Mn ion, leading to a possible model for water oxidation.
