Wu H M, Rätsep M, Young C S, Jankowiak R, Blankenship R E, Small G J
Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA.
Biophys J. 2000 Sep;79(3):1561-72. doi: 10.1016/S0006-3495(00)76407-1.
Results from high-pressure and Stark hole-burning experiments on isolated chlorosomes from the green sulfur bacterium Chlorobium tepidum are presented, as well as Stark hole-burning data for bacteriochlorophyll c (BChl c) monomers in a poly(vinyl butyral) copolymer film. Large linear pressure shift rates of -0.44 and -0.54 cm(-1)/MPa were observed for the chlorosome BChl c Q(y)-band at 100 K and the lowest Q(y)-exciton level at 12 K, respectively. It is argued that approximately half of the latter shift rate is due to electron exchange coupling between BChl c molecules. The similarity between the above shift rates and those observed for the B875 and B850 BChl a rings of the light-harvesting complexes of purple bacteria is emphasized. For BChl c monomer, fDeltamu++ = 0.35 D, where Deltamu+ is the dipole moment change for the Q(y) transition and f is the local field correction factor. The data establish that Deltamu+ is dominated by the matrix-induced contribution. The change in polarizability (Deltaalpha) for the Q(y) transition of the BChl c monomer is estimated at 19 A(3), which is essentially identical to that of the Chl a monomer. Interestingly, no Stark effects were observed for the lowest exciton level of the chlorosomes (maximum Stark field of 10(5) V/cm). Possible explanations for this are given, and these include consideration of structural models for the chlorosome BChl c aggregates.
本文展示了对来自嗜热绿硫菌的分离叶绿体进行高压和斯塔克烧孔实验的结果，以及聚（乙烯醇缩丁醛）共聚物薄膜中细菌叶绿素c（BChl c）单体的斯塔克烧孔数据。在100 K时，叶绿体BChl c Q(y)带和在12 K时最低的Q(y)激子能级分别观察到-0.44和-0.54 cm(-1)/MPa的大线性压力漂移率。有人认为，后一种漂移率的大约一半是由于BChl c分子之间的电子交换耦合。强调了上述漂移率与紫色细菌光捕获复合物的B875和B850 BChl a环所观察到的漂移率之间的相似性。对于BChl c单体，fDeltamu++ = 0.35 D，其中Deltamu+是Q(y)跃迁的偶极矩变化，f是局部场校正因子。数据表明Deltamu+主要由基质诱导贡献主导。BChl c单体Q(y)跃迁的极化率变化（Deltaalpha）估计为19 Å(3)，这与Chl a单体的极化率变化基本相同。有趣的是，对于叶绿体的最低激子能级（最大斯塔克场为10(5) V/cm）未观察到斯塔克效应。文中给出了对此的可能解释，其中包括对叶绿体BChl c聚集体结构模型的考虑。
