X-ray absorption spectroscopy on layered photosystem II membrane particlessuggests manganese-centered oxidation of the oxygen-evolving complex for the S-0-S-1, S-1-S-2, and S-2-S-3 transitions of the water oxidation cycle
L. Iuzzolino et al., X-ray absorption spectroscopy on layered photosystem II membrane particlessuggests manganese-centered oxidation of the oxygen-evolving complex for the S-0-S-1, S-1-S-2, and S-2-S-3 transitions of the water oxidation cycle, BIOCHEM, 37(49), 1998, pp. 17112-17119
By application of microsecond light flashes the oxygen-evolving complex (OE
C) was driven through its functional cycle, the S-state cycle. The S-state
population distribution obtained by the application of n flashes (n = 0 ...
6) was determined by analysis of EPR spectra; Mn K-edge X-ray absorption s
pectra were collected. Taking into consideration the likely statistical err
or in the data and the variability stemming from the use of three different
approaches for the determination of edge positions, we obtained an upshift
of the edge position by 0.8-1.5, 0.5-0.9, and 0.6-1.3 eV for the S-0-S-1,
S-1-S-2, and S-2-S-3 transitions, respectively, and a downshift by 2.3-3.1
eV for the S-3-S-0 transition. These results are highly suggestive of Mn ox
idation state changes for all four S-state transitions. In the So-state spe
ctrum, a clearly resolved shoulder in the X-ray spectrum around 6555 eV poi
nts toward the presence of Mn(II). We propose that photosynthetic oxygen ev
olution involves cycling of the photosystem II manganese complex through fo
ur distinct oxidation states of this tetranuclear complex: Mn(II)-Mn(III) -
Mn(IV)(2) in the So-state, Mn(III)(2)-Mn(IV)(2) in the S-1-state, Mn(III)(1
)-Mn(IV)(3) in the S-2-state, and Mn(IV)(4) in the S-3-state.