Jávorfi T, Garab G, Naqvi K R
Spectrochim Acta A Mol Biomol Spectrosc. 2000 Jan;56A(1):211-4. doi: 10.1016/s1386-1425(99)00226-7.
A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chla/b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chla) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chla neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chla/b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the TmS spectrum is concerned, spinach chloroplasts are by no means abnormal.
将大约三十年前记录的菠菜叶绿体的三线态减单线态（TmS）吸收光谱，与最近发表的分离的叶绿素a/b捕光复合物II（与高等植物光系统II相关的捕光复合物）的TmS光谱进行比较，结果表明这两种光谱非常相似，这是可以预料的，因为每种光谱仅由类胡萝卜素色素产生。尽管如此，比较也揭示了一个不同之处：样品的光激发是否会影响Qy区域（650 - 700纳米）的吸光度，这取决于样品是叶绿体悬浮液还是分离的捕光复合物II。应当指出的是，捕光复合物II的TmS光谱中的Qy信号与其余差光谱以相同的速率衰减，其最显著的特征是一个负峰。由于类胡萝卜素在Qy区域不吸收，该区域中信号的存在需要一个解释：范德沃斯、卡尔博内拉和霍夫是最先发现并深入研究该现象的人，他们将Qy信号归因于相邻类胡萝卜素（Car）上的三线态激发导致叶绿素a（Chla）分子吸收光谱的变化。如果叶绿体和捕光复合物II的行为差异具有可重复性，那就意味着产生叶绿体TmS光谱的类胡萝卜素三线态不会影响其相邻叶绿素a的吸收光谱。为了就这个棘手的问题得出确凿的结论，借助用于研究捕光复合物II的同一台动力学光谱仪对菠菜叶绿体和类囊体进行了检测；叶绿体和类囊体的TmS光谱都包含以680纳米为中心的显著漂白信号，并且每种情况下的三线态衰减时间与叶绿素a/b捕光复合物II三线态的衰减时间相当。回顾了与其他密切相关系统的相关结果，并得出结论：就TmS光谱的整体外观而言，菠菜叶绿体绝无异常。
