紫色光合细菌中类胡萝卜素的选择性分布及功能  

Selective Distribution and Physiological Function of Heterogeneous Carotenoids in Purple Photosynthetic Bacterium Rhodopseudomonas palustris

作　　者：冯娟[1] 李雪峰[1] 刘渊[1] 

机构地区：[1]电子科技大学生命科学与技术学院,四川成都610054

出　　处：《光谱学与光谱分析》2008年第7期1459-1463,共5页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金项目(20373079)资助

摘　　要：紫色光合细菌Rhodopseudomonas（Rps．）palustris光合膜中的外周捕光天线（LH2）及核心复合物（LH1-Rc）中都含有多种类胡萝卜素分子（Crt）。研究不同种类的Crt在上述色素蛋白复合物中的分布及其生理学功能具有重要意义。采用了高效液相色谱（HPLC）手段分析了中等光强（～4000lux）培养条件下所获得的Rps．palustris的LH2及LH1-RC中的Crt组成，发现共轭双键数目（n）为11或12的类胡萝卜素分子（包括lyeopene（n=11），Anhydrorhodivibrin（n=12）及Rhodopin（n=12）等，主要集中在LH2复合物中，而n=13的类胡萝卜素分子Spirilloxanthin则优先结合到LH1-RC中。通过将稳态吸收光谱及近红外荧光激发光谱在细菌叶绿素的Qx带处归一化，并比较两者的数值，发现在LH2中Crt从单重态向BCh1的传能效率[30．9％（v=0），25．4％（v=1），30．4％（v=2）]明显高于在LH1-RC中的传能效率[10．7％（v=0），7．8％（v=1），11．4％（v=2）]。此外，本文还运用亚微秒时间分辨吸收光谱检测了类胡萝卜素三重态Tn←T1吸收，发现伴随着532nm激光脉冲激发，LH1-RC和LH2中Crt三重态的吸收主峰位于571及560mn左右，它们分别归属于n=13和n=12的类胡萝卜素分子。通过对动力学衰减曲线进行单指数拟合，发现前者的衰减时间常数（1．6μs）明显短于后者（2．2μs）。上述研究结果表明，短链Crt易于结合到LH2中承担捕光的功能，而长链Crt优先结合到LH1-RC中发挥光保护功能。Purple photosynthetic bacterium Rhodopseudomonas （Rps.） palustris is unique in the heterogeneous carotenoid compositions in peripheral light-harvesting complex （LH2） and core complex （LH1-RC）. It is of great significance to investigate selective distribution and the physiological function of various carotenoids occurring in the pigment-protein complexes mentioned above. In the present paper, high performance liquid chromatogram （HPLC） was applied to analyze the carotenoid composition in LH2 and LH1-RC complexes isolated from Rps. palustris growing in medium light intensity. Comparison of the HPLC elution profiles showed that carotenoids having 11 or 12 conjugated double bonds, including lycopene （n= 11）, anhydrorhodivibrin （n = 12） and rhodopin （n= 12）, were the predominant components in LH2, whereas spirilloxanthin with n= 13 was preferentially bound to core complex. The average yields of carotenoid-to-BChl energy transfer in LH2 and LH1-RC were determined by comparing their steady-state absorption spectra and NIR fluorescence excitation spectroscopy, which were normalized at the BChl Qx transition. It was found that energy transfer yield decreased from 30. 9 %（v= 0）, 25.4 % （v= 1 ） and 30. 4 % （ v= 2） in LH2 complex to 10. 7% （v=0）, 7. 8% （v= 1） and 11.4% （v= 2） in LH1-RC complex, respectively. Additionally, triplet excited state carotenoids were investigated by means of sub-microsecond time-resolved absorption spectroscopy, where Tn←-T1 transient absorption maximum was observed at 571 nm for LH1-RC and 560 nm for LH2 complex at room temperature following the photo -excitation of carotenoid at 532 nm. The dynamic curves of these two spectral components, which were assignable to carotenoids with n= 13 and n= 12, could be well fitted to a single exponential decay function with the apparent time constants of 1.6 and 2. 2 μs, respectively. The aforementioned data suggested that heterogeneous carotenoids were selectively distributed in LH2 and core complex, wher

关 键 词：外周捕光天线(LH2) 核心复合物(LH1-RC) 选择性分布 传能效率 三重态 

分 类 号：S631.2[农业科学—蔬菜学]