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

Abstract

Background:Ca 2ϩ plays an essential role in oxygen evolution in photosystem II. Results: ENDOR spectra showed that some protons surrounding the manganese cluster are lost and modified by Ca

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

“…The line shape is similar to that of untreated PS II, , indicating that methanol does not replace the water molecules, previously assigned as the protons of W1–W4. At a glance, there are no spectral differences between the samples containing CH 3 OH and CD 3 OH, indicating that methanol does not affect the hydrogen-bond networks surrounding the W1–W4 site.…”

“…9 The interaction with the hydrogen-bonding network via W4 and Y Z located nearby would lower the reaction rate. 17 On the other hand, modification of the spin structure is not necessarily located close to Mn1 in the coupled spin system. The disruption of the hydrogen-bond network surrounding the Mn cluster would also cause the modification in the amplitude of Δ.…”

Magnetic structure of manganese cluster in photosystem II investigated by electron paramagnetic resonance

“…Ca 2+ depletion causes the loss of ENDOR signals assigned to the proton of W4 ( Fig. 5B ) [ 10 ], which connects Ca 2+ and Y Z directly. The role of Ca 2+ involves the maintenance of the hydrogen-bond network near the Ca 2+ site and the electron-transfer pathway to the Mn cluster.…”

“…If methanol is located in area I, close to Mn1, the structural modification via the amino acids surrounding Mn1 might cause modification of the hyperfine anisotropy of Mn1 [ 12 ]. The interaction with the hydrogen-bonding network via W4 and Y Z located nearby would lower the reaction rate [ 10 ]. On the other hand, modification of the spin structure is not necessary to be located close to Mn1 in a coupled spin system.…”

“… (A) ENDOR spectra of the S 2 state multiline in (black) untreated and (red) Ca 2+ -depleted PS II and (B) locations of the corresponded protons [ 10 , 16 ]. …”