Sujak A, Okulski W, Gruszecki W I
Department of Biophysics, Institute of Physics, Maria Curie-Skłodowska University, Lublin, Poland.
Biochim Biophys Acta. 2000 Dec 20;1509(1-2):255-63. doi: 10.1016/s0005-2736(00)00299-6.
Carotenoid pigments and in particular xanthophylls play several physiological functions in plant and animal membranes. Xanthophylls are present in biological membranes in the form of pigment-protein complexes but also as direct components of lipid phase. The biological activity of carotenoids in membranes depends on a molecular organisation of pigments in lipid bilayers, in particular the localisation, orientation and aggregational state. In the present work the organisation of lutein- and zeaxanthin-containing lipid membranes was analysed with the application of electronic absorption spectroscopy. Both xanthophyll pigments incorporated to the dipalmitoylphosphatidylcholine (DPPC) unilamellar liposomes form H-type molecular aggregates, manifested by the hypsochromic shift of the main absorption band of carotenoids. The aggregation of lutein and zeaxanthin in DPPC membranes was observed even at relatively low concentrations of a pigment in the lipid phase (1-5 mol%). Gaussian analysis of the absorption spectra of lutein and zeaxanthin in DPPC membranes in terms of the exciton splitting theory revealed the formation of different molecular structures of pigments interpreted as dimers, trimers, tetramers and large aggregates. The fraction of lutein and zeaxanthin in the monomeric form was found to depend on the physical state of the lipid phase. Pronounced monomerisation of lutein and zeaxanthin was observed as accompanying the transition from the P(beta)' phase to the L(alpha) phase of DPPC, mostly at the expense of the trimeric and tetrameric forms. The fraction of monomers of lutein is always lower by 10-30% than that of zeaxanthin under the same experimental conditions. Different organisational forms of lutein and zeaxanthin in the model system studied are discussed in terms of possible physiological functions of these pigments in the membranes of the retina: zeaxanthin in the protection of the lipid phase against oxidative damage and lutein in absorbing short wavelength radiation penetrating retina membranes.
类胡萝卜素色素，尤其是叶黄素，在植物和动物膜中发挥多种生理功能。叶黄素以色素 - 蛋白质复合物的形式存在于生物膜中，同时也是脂质相的直接成分。类胡萝卜素在膜中的生物活性取决于色素在脂质双层中的分子组织，特别是其定位、取向和聚集状态。在本研究中，应用电子吸收光谱分析了含叶黄素和玉米黄质的脂质膜的组织情况。两种叶黄素色素掺入二棕榈酰磷脂酰胆碱（DPPC）单层脂质体中均形成H型分子聚集体，表现为类胡萝卜素主吸收带的蓝移。即使在脂质相中色素浓度相对较低（1 - 5摩尔％）时，也观察到叶黄素和玉米黄质在DPPC膜中的聚集。根据激子分裂理论对DPPC膜中叶黄素和玉米黄质的吸收光谱进行高斯分析，揭示了色素形成的不同分子结构，可解释为二聚体、三聚体、四聚体和大聚集体。发现叶黄素和玉米黄质单体形式的比例取决于脂质相的物理状态。观察到随着DPPC从P(β)'相转变为L(α)相，叶黄素和玉米黄质明显单体化，主要是以三聚体和四聚体形式减少为代价。在相同实验条件下，叶黄素单体的比例总是比玉米黄质低10 - 30％。根据这些色素在视网膜膜中可能的生理功能，讨论了所研究模型系统中叶黄素和玉米黄质的不同组织形式：玉米黄质用于保护脂质相免受氧化损伤，叶黄素用于吸收穿透视网膜膜的短波长辐射。
