The Y(Z)-tyrosine radical was trapped by freezing immediately after illumination in Ca2+-depleted Photosystem II (PS II) membranes and the pH-dependent characteristics of the radical were investigated using CW-EPR and pulsed ENDOR. The spectrum of the Y.(Z) radical trapped in the Y.(Z)S1 state at pH 5.5 was cation-like as reported in Mn-depleted PS II (H. Mino et al., Spectrochim. Acta A 53 (1997) 1465-1483). By illuminating the PS II-retaining S2 state, the Y.(Z) radical and a broad doublet signal formed in the g~2 region were trapped concomitantly. The spectrum of the trapped Y.(Z) radical in the Y.(Z)S2 state was cation-like at pH 5.5 but the pulsed ENDOR measurements reveals the involvement of the neutral Y.(Z) radical in the doublet signal. At pH 7.0, the resulting Y.(Z) signal was the mixture of the cation-like and neutral radical spectra, and considerably different from the neutral radical found in Mn-depleted PS II. pH-Dependent changes in the properties of the Y.(Z) radical are discussed in relation to the redox events occurring in Ca2+-depleted PS II. Copyright (C) 2000 Elsevier Science B.V.
Mino, H., Kawamori, A., & Ono, T. A. (2000). pH-Dependent characteristics of Y(Z) radical in Ca2+-depleted Photosystem II studied by CW-EPR and pulsed ENDOR. Biochimica et Biophysica Acta - Bioenergetics, 1457(3), 157–165. https://doi.org/10.1016/S0005-2728(00)00074-8