Tomo Tatsuya, Kato Yuki, Suzuki Takehiro, Akimoto Seiji, Okubo Tatsunori, Noguchi Takumi, Hasegawa Koji, Tsuchiya Tohru, Tanaka Kazunori, Fukuya Michitaka, Dohmae Naoshi, Watanabe Tadashi, Mimuro Mamoru
Department of Technology and Ecology, Hall of Global Environmental Research, Kyoto University, Kyoto, Japan.
J Biol Chem. 2008 Jun 27;283(26):18198-209. doi: 10.1074/jbc.M801805200. Epub 2008 May 5.
Photochemically active photosystem (PS) I complexes were purified from the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina MBIC 11017, and several of their properties were characterized. PS I complexes consist of 11 subunits, including PsaK1 and PsaK2; a new small subunit was identified and named Psa27. The new subunit might replace the function of PsaI that is absent in A. marina. The amounts of pigments per one molecule of Chl d' were 97.0 +/- 11.0 Chl d, 1.9 +/- 0.5 Chl a, 25.2 +/- 2.4 alpha-carotene, and two phylloquinone molecules. The light-induced Fourier transform infrared difference spectroscopy and light-induced difference absorption spectra reconfirmed that the primary electron donor of PS I (P740) was the Chl d dimer. In addition to P740, the difference spectrum contained an additional band at 728 nm. The redox potentials of P740 were estimated to be 439 mV by spectroelectrochemistry; this value was comparable with the potential of P700 in other cyanobacteria and higher plants. This suggests that the overall energetics of the PS I reaction were adjusted to the electron acceptor side to utilize the lower light energy gained by P740. The distribution of charge in P740 was estimated by a density functional theory calculation, and a partial localization of charge was predicted to P1 Chl (special pair Chl on PsaA). Based on differences in the protein matrix and optical properties of P740, construction of the PS I core in A. marina was discussed.
从以叶绿素（Chl）d为主的蓝藻菌滨海栖热袍菌MBIC 11017中纯化出具有光化学活性的光系统（PS）I复合物，并对其若干特性进行了表征。PS I复合物由11个亚基组成，包括PsaK1和PsaK2；鉴定出一个新的小亚基并将其命名为Psa27。这个新亚基可能取代了滨海栖热袍菌中不存在的PsaI的功能。每一个Chl d'分子的色素含量为97.0±11.0个Chl d、1.9±0.5个Chl a、25.2±2.4个α-胡萝卜素和两个叶醌分子。光诱导傅里叶变换红外差光谱和光诱导差吸收光谱再次证实PS I的原初电子供体（P740）是Chl d二聚体。除了P740，差光谱在728 nm处还包含一个额外的谱带。通过光谱电化学估计P740的氧化还原电位为439 mV；该值与其他蓝藻菌和高等植物中P700的电位相当。这表明PS I反应的整体能量学被调整到电子受体一侧，以利用P740获得的较低光能。通过密度泛函理论计算估计了P740中的电荷分布，并预测电荷部分定位于P1 Chl（PsaA上的特殊对Chl）。基于P740的蛋白质基质和光学性质的差异，讨论了滨海栖热袍菌中PS I核心的构建。
