The structure and activation of substrate water molecules in the S2 state of photosystem II studied by hyperfine sublevel correlation spectroscopy

Proton Matrix ENDOR Studies on Ca2+-depleted and Sr2+-substituted Manganese Cluster in Photosystem II

“…We detected six pairs of proton hyperfine signals in the untreated PSII membranes by the proton matrix ENDOR (37,38), which is similar to the number of protons detected by HYSCORE (39). Curiously, only a small number of the signals was detected in highly resolved CW-ENDOR spectra within ϳ4 MHz hyperfine couplings, i.e.…”

“…The protons in the W3 and W4 molecules are in close proximity to each other, and the location of the protons in the DFT calculations is strongly dependent on the structural models employed (42,48,59,60). Lakshmi and co-workers (39,61) reported HYSCORE results of the S 2 state multiline signal, where similar proton signals to those of the proton matrix ENDOR were detected. However, the assignments of these signals are significantly different from those in the ENDOR assignments (37,39,61).…”

“…Lakshmi and co-workers (39,61) reported HYSCORE results of the S 2 state multiline signal, where similar proton signals to those of the proton matrix ENDOR were detected. However, the assignments of these signals are significantly different from those in the ENDOR assignments (37,39,61). The causes underlying these experimental differences and the assignments of these signals are unknown.…”

“…We have assigned a W2 proton to the 4 MHz hyperfine couplings, W1 and W3 protons to 2-3 MHz hyperfine couplings, and W4 protons to 0.7, 1.36 MHz hyperfine couplings, respectively (37), whereas the DFT models assigned the W1 and W2 protons to the 4 MHz hyperfine separations in the presence of isotropic hyperfine couplings, and W3 and W4 protons to 1-2 MHz hyperfine separations (42). In addition, Milikisiyants et al (39) assigned the hyperfine signals with 4-MHz separation to the His 332 proton because it has a very small isotropic hyperfine parameter determined by HYSCORE.…”

“…On the other hand, the sign of the spin densities was inconsistent between the pulsed ELDOR results (30) and theoretical studies, because the former showed a spin topology of ␣␤␣␤, whereas the latter showed a ␣␤␤␣ topology. This inconsistency resulted in slightly different hyperfine parameters for the protons (27,39,42). We have assigned a W2 proton to the 4 MHz hyperfine couplings, W1 and W3 protons to 2-3 MHz hyperfine couplings, and W4 protons to 0.7, 1.36 MHz hyperfine couplings, respectively (37), whereas the DFT models assigned the W1 and W2 protons to the 4 MHz hyperfine separations in the presence of isotropic hyperfine couplings, and W3 and W4 protons to 1-2 MHz hyperfine separations (42).…”