Location of Methanol on the S2 State Mn Cluster in Photosystem II Studied by Proton Matrix Electron Nuclear Double Resonance

Proton matrix electron nuclear double resonance (ENDOR) spectroscopy was performed to specify the location of the methanol molecule near the manganese cluster in photosystem II. Comparison of the ENDOR spectra in the presence of CH3OH and CD3OH revealed two pairs of hyperfine couplings, 1.2 MHz for A(perpendicular to) and 2.5 MHz for A(//), arising from the methyl group in methanol. On the basis of the crystal structure, the possible location of methanol close to the manganese cluster was discussed.