Determination of the distance between Yox⋅ Z and Q−⋅ A in photosystem II by pulsed EPR spectroscopy on light‐induced radical pairs

摘要

>Out-of-phase electron spin echo envelope modulation (ESEEM) spectroscopy was used to determine the distances within two consecutive radical pair states initiated by a laser flash in photosystem II membrane fragments at pH 11. The distance between the spin density centers of the primary electron donor cation radical, P+⋅ ₆₈₀, and the reduced plastoquinone acceptor, Q−⋅ _A, has been found to be 27.7±0.7 Å in agreement with previous results. Near room temperature and at high pH, P+⋅ ₆₈₀ is reduced by Y_Z, a redox active tyrosine residue, on a sub-microsecond timescale. As a consequence, the subsequent radical pair state, Yox⋅ _ZQ−⋅ _A, could be investigated after almost complete reduction of P+⋅ ₆₈₀ by Y_Z. The determined dipolar electronic spin-spin coupling within the radical pair Yox⋅ _ZQ−⋅ _A corresponds to a distance of 34±1 Å between the two molecules.