Fourier Transform Infrared Spectrum of the Secondary Quinone Electron Acceptor QB in Photosystem II
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- 作者：Hiroyuki Suzuki ; Masa-aki Nagasaka ; Miwa Sugiura ; and Takumi Noguchi
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：August 30, 2005
- 年：2005
- 卷：44
- 期：34
- 页码：11323 - 11328
- 全文大小：88K
- 年卷期：v.44,no.34(August 30, 2005)
- ISSN：1520-4995
文摘
Fourier transform infrared difference spectra upon single reduction of the secondary quinoneelectron acceptor QB in photosystem II (PSII), without a contribution from the electron donor-side signals,were obtained for the first time using Mn-depleted PSII core complexes of the thermophilic cyanobacteriumThermosynechococcus elongatus. The QB-/QB difference spectrum exhibited a strong 
1237ge10001.gif"> stretchingband of the semiquinone anion at 1480 cm-1, the frequency higher by 2 cm-1 than that of the correspondingband of QA-, in agreement with the previous S2QB-/S1QB spectrum of the PSII membranes of spinach[Zhang, H., Fischer, G., and Wydrzynski, T. (1998) Biochemistry 37, 5511-5517]. Also, several peaksoriginating from the Fermi resonance of coupled His modes with its strongly H-bonded NH vibrationwere observed in the 2900-2600 cm-1 region, where the peak frequencies were higher by 7-24 cm-1compared with those of the QA-/QA spectrum. These frequency differences suggest that H-bond interactionsof the CO groups, especially with a His side chain, are different between QB- and QA-. Furthermore, aprominent positive peak was observed at 1745 cm-1 in the C=O stretching region of COOH or estergroups in the QB-/QB spectrum. The peak frequency was unaffected by D2O substitution, indicating thatthis peak does not arise from a COOH group but probably from the 10a-ester C=O group of the pheophytinmolecule adjacent to QB. The absence of protonation of carboxylic amino acids upon QB- formation incontrast to the previous observation in the purple bacterium Rhodobacter sphaeroides suggests that theprotonation mechanism of QB in PSII is different from that of bacterial reaction centers.