van Noort P I, Zhu Y, LoBrutto R, Blankenship R E
Department of Chemistry and Biochemistry, Arizona State University, Tempe 85287-1604, USA.
Biophys J. 1997 Jan;72(1):316-25. doi: 10.1016/S0006-3495(97)78670-3.
Oligomers of [E,E] BChl CF (8, 12-diethyl bacteriochlorophyll c esterified with farnesol (F)) and [Pr,E] BChl CF (analogously, M methyl, Pr propyl) in hexane and aqueous detergent or lipid micelles were studied by means of steady-state absorption, time-resolved fluorescence, and electron spin resonance spectroscopy. The maximum absorption wavelength, excited-state dynamics, and electron spin resonance (EPR) linewidths are similar to those of native and reconstituted chlorosomes of Chlorobium tepidum. The maximum absorption wavelength of oligomers of [E,E] BChl CF was consistently blue-shifted as compared to that of [Pr,E] BChl CF oligomers, which is ascribed to the formation of smaller oligomers with [E,E] BChl CF than [Pr,E] BChl CF. Time-resolved fluorescence measurements show an excited-state lifetime of 10 ps or less in nonreduced samples of native and reconstituted chlorosomes of Chlorobium tepidum. Under reduced conditions the excited-state lifetime increased to tens of picoseconds, and energy transfer to BChl a or long-wavelength absorbing BChl c was observed. Oligomers of [E,E] BChl CF and [Pr,E] BChl CF in aqueous detergent or lipid micelles show a similar short excited-state lifetime under nonreduced conditions and an increase up to several tens of picoseconds upon reduction. These results indicate rapid quenching of excitation energy in nonreduced samples of chlorosomes and aqueous BChl c oligomers. EPR spectroscopy shows that traces of oxidized BChl c radicals are present in nonreduced and absent in reduced samples of chlorosomes and BChl c oligomers. This suggests that the observed short excited-state lifetimes in nonreduced samples of chlorosomes and BChl c oligomers may be ascribed to excited-state quenching by BChl c radicals. The narrow EPR linewidth suggests that the BChl c are arranged in clusters of 16 and 6 molecules in chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, respectively.
通过稳态吸收、时间分辨荧光和电子自旋共振光谱法研究了己烷以及水性去污剂或脂质胶束中[E,E] BChl CF（法尼醇（F）酯化的8,12 - 二乙基细菌叶绿素c）和[Pr,E] BChl CF（类似地，M为甲基，Pr为丙基）的低聚物。其最大吸收波长、激发态动力学和电子自旋共振（EPR）线宽与嗜热绿菌天然和重组的叶绿体相似。与[Pr,E] BChl CF低聚物相比，[E,E] BChl CF低聚物的最大吸收波长持续蓝移，这归因于[E,E] BChl CF形成的低聚物比[Pr,E] BChl CF更小。时间分辨荧光测量表明，嗜热绿菌天然和重组叶绿体的未还原样品中激发态寿命为10皮秒或更短。在还原条件下，激发态寿命增加到几十皮秒，并且观察到能量转移到BChl a或吸收长波长的BChl c。水性去污剂或脂质胶束中的[E,E] BChl CF和[Pr,E] BChl CF低聚物在未还原条件下显示出类似的短激发态寿命，还原后增加到几十皮秒。这些结果表明叶绿体和水性BChl c低聚物的未还原样品中激发能的快速猝灭。EPR光谱表明，叶绿体和BChl c低聚物的未还原样品中存在痕量氧化的BChl c自由基，而还原样品中不存在。这表明在叶绿体和BChl c低聚物的未还原样品中观察到的短激发态寿命可能归因于BChl c自由基的激发态猝灭。窄的EPR线宽表明，在嗜热绿菌和橙色绿屈挠菌的叶绿体中，BChl c分别以16和6分子簇的形式排列。
