Cherepy N J, Shreve A P, Moore L J, Boxer S G, Mathies R A
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Biochemistry. 1997 Jul 15;36(28):8559-66. doi: 10.1021/bi970024r.
Qy-excited resonance Raman spectra of the accessory bacteriochlorophylls (B), the bacteriopheophytins (H), and the primary electron donor (P) in the bacterial photosynthetic reaction center (RC) of Rhodobacter sphaeroides have been obtained at 95 and 278 K. Frequency and intensity differences are observed in the low-frequency region of the P vibrational spectrum when the sample is cooled from 278 to 95 K. The B and H spectra exhibit minimal changes of frequencies and relative intensities as a function of temperature. The mode patterns in the Raman spectra of B and H differ very little from Raman spectra of the chromophores in vitro. The Raman scattering cross sections of B and H are 6-7 times larger than those for analogous modes of P at 278 K. The cross sections of B and of H are 3-4 times larger at 95 K than at 278 K, while the cross sections of P are approximately constant with temperature. The temperature dependence of the Raman cross sections for B and H suggests that pure dephasing arising from coupling to low-frequency solvent/protein modes is important in the damping of their excited states. The weak Raman cross sections of the special pair suggest that the excited state of P is damped by very rapid (<<30 fs) electronic relaxation processes. These resonance Raman spectra provide information for developing multimode vibronic models of the excited-state structure and dynamics of the chromophores in the RC.
已在95K和278K下获得了球形红细菌光合反应中心（RC）中辅助细菌叶绿素（B）、细菌脱镁叶绿素（H）和初级电子供体（P）的Qy激发共振拉曼光谱。当样品从278K冷却到95K时，在P振动光谱的低频区域观察到频率和强度差异。B和H光谱随温度变化时，频率和相对强度的变化最小。B和H的拉曼光谱中的模式图案与体外发色团的拉曼光谱差异很小。在278K时，B和H的拉曼散射截面比P的类似模式大6-7倍。在95K时，B和H的截面比在278K时大3-4倍，而P的截面随温度大致恒定。B和H的拉曼截面的温度依赖性表明，与低频溶剂/蛋白质模式耦合产生的纯退相在其激发态的衰减中很重要。特殊对的弱拉曼截面表明，P的激发态通过非常快速（<<30 fs）的电子弛豫过程被衰减。这些共振拉曼光谱为开发RC中发色团激发态结构和动力学的多模振动电子模型提供了信息。
