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Redox Potentials of Chlorophylls and β-Carotene in the Antenna Complexes of Photosystem II
journal contribution
posted on 2005-02-16, 00:00 authored by Hiroshi Ishikita, Ernst-Walter KnappElectron transfer (ET) processes in reaction centers (RC) of photosystem II (PSII) are prerequisites
of oxygen generation. They are promoted by energy transfer from antenna to RC. Here, we calculated the
redox potentials of chlorophylla/β-carotene (Chla/Car) in PSII CP43/CP47 antenna complexes, solving the
linearized Poisson−Boltzmann (LPB) equation based on the PSII crystal structure. The majority of antenna
Chla redox potentials for reduction/oxidation were lower than those of RC Chla. Hence, ET events with
excess electrons remain localized in the RC. Simultaneously antenna Chla can serve as an efficient cation
sink to rereduce RC Chla if normal PSII function is inhibited. Especially three antenna Chla (Chl-47, Chl-18, and Chl-12) and two Car bridging the space between ChlZ(D1) and cytochrome (cyt) b559 have the
same level of oxidation redox potential. Together with ChlZ(D2) they form an electron hole transfer pathway
and temporary storage device guiding from the oxidized P680+• Chla to the cyt b559. This path may play
a photoprotective role as efficient electron hole quencher.