Peterman E J, Dukker F M, van Grondelle R, van Amerongen H
Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, The Netherlands.
Biophys J. 1995 Dec;69(6):2670-8. doi: 10.1016/S0006-3495(95)80138-4.
Laser-flash-induced transient absorption measurements were performed on trimeric light-harvesting complex II to study carotenoid (Car) and chlorophyll (Chl) triplet states as a function of temperature. In these complexes efficient transfer of triplets from Chl to Car occurs as a protection mechanism against singlet oxygen formation. It appears that at room temperature all triplets are being transferred from Chl to Car; at lower temperatures (77 K and below) the transfer is less efficient and chlorophyll triplets can be observed. In the presence of oxygen at room temperature the Car triplets are partly quenched by oxygen and two different Car triplet spectral species can be distinguished because of a difference in quenching rate. One of these spectral species is replaced by another one upon cooling to 4 Ki demonstrating that at least three carotenoids are in close contact with chlorophylls. The triplet minus singlet absorption (T-S) spectra show maxima at 504-506 nm and 517-523 nm, respectively. In the Chl Qy region absorption changes can be observed that are caused by Car triplets. The T-S spectra in the Chl region show an interesting temperature dependence which indicates that various Car's are in contact with different Chl a molecules. The results are discussed in terms of the crystal structure of light-harvesting complex II.
对三聚体捕光复合物II进行了激光闪光诱导瞬态吸收测量，以研究类胡萝卜素（Car）和叶绿素（Chl）三线态随温度的变化。在这些复合物中，三线态从Chl到Car的有效转移作为一种防止单线态氧形成的保护机制而发生。似乎在室温下所有三线态都从Chl转移到Car；在较低温度（77 K及以下）下，转移效率较低，可以观察到叶绿素三线态。在室温下有氧存在时，Car三线态会被氧部分猝灭，由于猝灭速率的差异，可以区分出两种不同的Car三线态光谱物种。冷却到4 K时，其中一种光谱物种会被另一种取代，这表明至少有三种类胡萝卜素与叶绿素紧密接触。三线态减单线态吸收（T-S）光谱分别在504 - 506 nm和517 - 523 nm处出现最大值。在Chl Qy区域可以观察到由Car三线态引起的吸收变化。Chl区域的T-S光谱显示出有趣的温度依赖性，这表明不同的Car与不同的Chl a分子接触。根据捕光复合物II的晶体结构对结果进行了讨论。
