bi047922p_si_001.pdf (145.34 kB)
Redox Potentials of Chlorophylls in the Photosystem II Reaction Center†
journal contribution
posted on 2005-03-15, 00:00 authored by Hiroshi Ishikita, Bernhard Loll, Jacek Biesiadka, Wolfram Saenger, Ernst-Walter KnappWater oxidation generating atmospheric oxygen occurs in photosystem II (PSII), a large protein−pigment complex located in the thylakoid membrane. The recent crystal structures at 3.2 and 3.5 Å
resolutions provide novel details on amino acid side chains, especially in the D1/D2 subunits. We calculated
the redox potentials for one-electron oxidation of the chlorophyll a (Chla) molecules in PSII, considering
the protein environment in atomic detail. The calculated redox potentials for the dimer Chla (PD1/D2) and
accessory Chla (ChlD1/D2) were 1.11−1.30 V relative to the normal hydrogen electrode at pH 7, which is
high enough for water oxidation. The D1/D2 proteins and their cofactors contribute approximately 390
mV to the enormous upshift of 470 mV compared to the redox potential of monomeric Chla in
dimethylformamide. The other subunits are responsible for the remaining 80 mV. The high redox potentials
of the two accessory Chla ChlD1/D2 suggests that they also participate in the charge separation process.