Kirmaier C, Gaul D, DeBey R, Holten D, Schenck C C
Department of Chemistry, Washington University St. Louis, MO 63130.
Science. 1991 Feb 22;251(4996):922-7. doi: 10.1126/science.2000491.
Site-directed mutagenic replacement of M subunit Leu214 by His in the photosynthetic reaction center (RC) from Rhodobacter sphaeroides results in incorporation of a bacteriochlorophyll molecule (BChl) in place of the native bacteriopheophytin (BPh) electron acceptor. Evidence supporting this conclusion includes the ground-state absorption spectrum of the (M)L214H mutant, pigment and metal analyses, and time-resolved optical experiments. The genetically modified RC supports transmembrane charge separation from the photoexcited BChl dimer to the primary quinone through the new BChl molecule, but with a reduced quantum yield of 60 percent (compared to 100 percent in wild-type RCs). These results have important implications for the mechanism of charge separation in the RC, and rationalize the choice of (bacterio)pheophytins as electron acceptors in a variety of photosynthetic systems.
在球形红细菌光合反应中心（RC）中，通过定点诱变将M亚基的亮氨酸214替换为组氨酸，结果导致一个细菌叶绿素分子（BChl）取代了天然的细菌脱镁叶绿素（BPh）电子受体。支持这一结论的证据包括（M）L214H突变体的基态吸收光谱、色素和金属分析以及时间分辨光学实验。经基因改造的RC支持通过新的BChl分子从光激发的BChl二聚体到初级醌的跨膜电荷分离，但量子产率降低至60%（野生型RC为100%）。这些结果对RC中电荷分离机制具有重要意义，并解释了在各种光合系统中选择（细菌）脱镁叶绿素作为电子受体的原因。
