XANES (X-ray Absorption Near-Edge Structure) in Biophysics
Photosynthetic enzymes containing manganese have been studied by XANES for
many years, and various model structures of the photosynthetic oxygen
evolving manganese cluster have been proposed. High-resolution XANES
with light illumination experiments have recently provided new insight on
Mn valency. The first observation of a cyclic shift of the Mn K-edge
associated with laser illumination showed that the oxidation state of
Mn does oscillate during a four-electron cycling reaction induced by photons,
corresponding to the well known "oxygen clock" mechanism proposed
by Joliot & Kok.
Mn K-XANES spectra for O2-evolving photosystem II (PSII) membranes
after a series of flashes, which demonstrates the first observation
of a cyclic shift of the Mn K-edge associated with laser illumination.
These results evidenced that the oxidation state of Mn does oscillate
during a four-electron cycling reaction induced by photons.
Oscillation of the Mn K-edge energy of PSII membranes under
single-turnover flashes. The half-height energies of Mn K-edge
spectra after zero to five flashes (
) were compared
with the simulated values (
).
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