Redox Potentials of Chlorophylls in the Photosystem II Reaction Center

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• 作者：Hiroshi Ishikita ; Bernhard Loll ; Jacek Biesiadka ; Wolfram Saenger ; and Ernst-Walter Knapp
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：March 15, 2005
• 年：2005
• 卷：44
• 期：10
• 页码：4118 - 4124
• 全文大小：165K
• 年卷期：v.44,no.10(March 15, 2005)
• ISSN：1520-4995

文摘

Water 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 Åresolutions provide novel details on amino acid side chains, especially in the D1/D2 subunits. We calculatedthe redox potentials for one-electron oxidation of the chlorophyll a (Chla) molecules in PSII, consideringthe protein environment in atomic detail. The calculated redox potentials for the dimer Chla (P_D1/D2) andaccessory Chla (Chl_D1/D2) were 1.11-1.30 V relative to the normal hydrogen electrode at pH 7, which ishigh enough for water oxidation. The D1/D2 proteins and their cofactors contribute approximately 390mV to the enormous upshift of 470 mV compared to the redox potential of monomeric Chla indimethylformamide. The other subunits are responsible for the remaining 80 mV. The high redox potentialsof the two accessory Chla Chl_D1/D2 suggests that they also participate in the charge separation process.