van Brederode M E, van Stokkum I H, Katilius E, van Mourik F, Jones M R, van Grondelle R
Faculty of Sciences, Division of Physics and Astronomy, Department of Biophysics, Vrije Universiteit, Amsterdam, The Netherlands.
Biochemistry. 1999 Jun 8;38(23):7545-55. doi: 10.1021/bi9829128.
Energy transfer and the primary charge separation process are studied as a function of excitation wavelength in membrane-bound reaction centers of Rhodobacter sphaeroides in which the excitonically coupled bacteriochlorophyll homodimer is converted to a bacteriochlorophyll-bacteriopheophytin heterodimer, denoted D [Bylina, E. J., and Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S. A. 85, 7226]. In the HM202L heterodimer reaction center, excitation of D using 880 nm excitation light results in a 43 ps decay of the excited heterodimer, D. The decay of D results for about 30% in the formation of the charge separated state D+QA- and for about 70% in a decay directly to the ground state. Upon excitation of the monomeric bacteriochlorophylls using 798 nm excitation light, approximately 60% of the excitation energy is transferred downhill to D, forming D. Clear evidence is obtained that the other 40% of the excitations results in the formation of D+QA- via the pathway BA --> BA+HA- --> D+HA- --> D+QA-. In the membrane-bound "reversed" heterodimer reaction center HL173L, the simplest interpretation of the transient absorption spectra following B excitation is that charge separation occurs solely via the slow D-driven route. However, since a bleach at 812 nm is associated with the spectrum of D in the HL173L reaction center, it cannot be excluded that a state including BB is involved in the charge separation process in this complex.
在球形红细菌的膜结合反应中心中，研究了能量转移和初级电荷分离过程与激发波长的关系。在该反应中心中，激子耦合的细菌叶绿素同二聚体转变为细菌叶绿素 - 细菌脱镁叶绿素异二聚体，记为D [Bylina, E. J., and Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S. A. 85, 7226]。在HM202L异二聚体反应中心，用880 nm激发光激发D会导致激发态异二聚体D有43 ps的衰减。D的衰减约30%导致电荷分离态D+QA-的形成，约70%直接衰减回基态。用798 nm激发光激发单体细菌叶绿素时，约60%的激发能量会向下转移至D，形成D。有明确证据表明，另外40%的激发通过BA --> BA+HA- --> D+HA- --> D+QA-途径导致D+QA-的形成。在膜结合的“反向”异二聚体反应中心HL173L中，对B激发后的瞬态吸收光谱的最简单解释是电荷分离仅通过缓慢的D驱动途径发生。然而，由于812 nm处的漂白与HL173L反应中心中D的光谱相关，所以不能排除包含BB的状态参与该复合物电荷分离过程的可能性。
