Struck A, Cmiel E, Katheder I, Scheer H
Botanisches Institut, Universität, München, FRG.
FEBS Lett. 1990 Jul 30;268(1):180-4. doi: 10.1016/0014-5793(90)81003-7.
Monomeric bacteriochlorophylls BA and BB in photosynthetic reaction centers from Rhodobacter sphaeroides R26 were exchanged with (13(2)-hydroxy-)bacteriochlorophylls containing a 3-vinyl- or 3-(alpha-hydroxyethyl)-substituent instead of the 3-acetyl group. The corresponding binding sites must be tolerant to the introduction of the polar residue at C-13(2) and modifications of the 3-acetyl group. According to HPLC analysis, the exchange with both pigments amounts to less than or equal to 50% of the total BChl contained in the complex, corresponding to less than or equal to 100% of the monomeric BChl alpha BA,B. The absorption spectra show significant changes in the QX and QY-region of the monomeric bacteriochlorophylls. By contrast, the absorption of the primary donor (P870) and reversible photobleaching is retained. The circular dichroism is also unchanged in the 870 nm region. The positive cd band located at around 800 nm in native reaction centers, shifts with the (blue-shifted) QY absorption(s) of BA and/or BB, whereas the position of the negative one remains nearly unaffected. The data indicate that the latter is the upper excitonic band of the primary donor, and that there is little interaction of the monomeric BA/BB with the primary donor.
来自球形红杆菌R26光合反应中心的单体细菌叶绿素BA和BB，被含有3-乙烯基或3-(α-羟乙基)取代基而非3-乙酰基的(13(2)-羟基-)细菌叶绿素所取代。相应的结合位点必须能够耐受在C-13(2)处引入极性残基以及对3-乙酰基的修饰。根据高效液相色谱分析，两种色素的交换量均小于或等于复合物中所含总细菌叶绿素的50%，相当于单体细菌叶绿素α BA,B的小于或等于100%。吸收光谱显示单体细菌叶绿素的QX和QY区域有显著变化。相比之下，初级供体（P870）的吸收和可逆光漂白得以保留。在870 nm区域，圆二色性也未发生变化。天然反应中心中位于800 nm左右的正cd带，随着BA和/或BB的（蓝移）QY吸收而移动，而负带的位置几乎不受影响。数据表明，后者是初级供体的上激子带，且单体BA/BB与初级供体之间几乎没有相互作用。
