Photochemistry of a Bacterial Photosynthetic Reaction Center Missing the Initial Bacteriochlorophyll Electron Acceptor

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• 作者：Brett Carter ; Steven G. Boxer ; Dewey Holten ; Christine Kirmaier
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：August 23, 2012
• 年：2012
• 卷：116
• 期：33
• 页码：9971-9982
• 全文大小：649K
• 年卷期：v.116,no.33(August 23, 2012)
• ISSN：1520-5207

文摘

A novel chromophore composition of the bacterial photosynthetic reaction center (RC) has been discovered: RCs lacking the L-side monomeric bacteriochlorophyll chromophore result from mutation of the native isoleucine at M204 to glutamine in Rhodobacter capsulatus. This conclusion is obtained from 77 K UV鈥搗is spectroscopy and pigment extractions of the I(M204)Q mutant and seven variants containing the I(M204)Q plus other mutations. The oxidation potential of the primary electron donor P (a dimer of bacteriochlorophylls) was measured for three of the mutants and found to be 50鈥?5 mV lower than in wild-type RCs. Ultrafast transient absorption measurements reveal (minimally) two subpopulations of P* that have distinct lifetimes and photochemical outcomes for all mutants containing I(M204)Q. In one subpopulation P* decays solely by internal conversion to the ground state. In the other subpopulation P* decays by electron transfer to the normally inactive M-side bacteriopheophytin (H_M) in competition with internal conversion to the ground state. When a Tyr residue is substituted for the native Phe at L181 near the M-side monomeric bacteriochlorophyll (B_M), the rate of electron transfer to H_M is increased about 4-fold.