Molecular Structure of the S2 State with a g = 5 Signal in the Oxygen Evolving Complex of Photosystem II

The g-factor shift of the g = 4.1 EPR signal was detected in spinach PsbO/P/Q-depleted PS II. The effective g-factor of the signal shifts up to ∼4.9, depending on the Ca2+ concentration. Hyperfine structure spacing with about 3 mT was detected in this g = 5 (4.9) signal. The shift to g = 5 (4.9) was related to the distortion of the manganese cluster, derived from the modification of the chemical bond or the crystalline field of the Mn4­(III) in the manganese cluster. Based on the EPR analysis of the g = 5 (4.9) spin state, another molecular structure of the S2 state, a “distant Mn” structure, was discussed as an intermediate state between the S2 and S3 states.