Abstract
The molecular mechanism of photosynthetic water oxidation still remains unclear. For its clarification, it is important to reveal the reactions of water at molecular level. Here, we attempted to detect the reactions of water in the water oxidizing complex (WOC) using Fourier transform infrared spectroscopy (FTIR).
FTIR difference spectra of flash-induced S-state transitions were measured using hydrated PSII core complexes from Synechococcus elongatus. The spectra showed a differential signal at 3617/3588 cm-1 upon 1st flash and negative peaks at 3634, 3621, 3612 cm-1 upon 2nd, 3rd and 4th flash, respectively. These bands downshifted by ~940 and ~10 cm-1 upon D2O and H218O exchange, respectively, indicating that the bands arise from water coupled to the Mn-cluster. The different wavenumbers and the mostly negative intensities were interpreted as due to substrate water with specific structures. Thus, FTIR is a promising method to investigate the mechanism of photosynthetic water oxidation.
