Aranda F J, Sánchez-Migallón M P, Gómez-Fernández J C
Departamento de Bioquímica y Biología Molecular A, Facultad de Veterinaria, Universidad de Murcia, Spain.
Arch Biochem Biophys. 1996 Sep 15;333(2):394-400. doi: 10.1006/abbi.1996.0406.
The effect of alpha-tocopherol on the Ca(2+)-induced fusion of large unilamellar phosphatidylserine vesicles has been investigated. Mixing of aqueous vesicle contents was followed continually with the terbium-dipicolinic acid (Tb-DPA) assay, while the dissociation of preencapsulated Tb-DPA complex was taken as a measure of the release of vesicle contents. Vesicles consisting of pure phosphatidylserine and phosphatidylserine containing 2, 5, and 10 mol% of alpha-tocopherol were employed at different Ca2+ concentrations. The presence of low amounts of alpha-tocopherol decreased the initial rate of fusion without changing the Ca2+ threshold concentration. The reduction of the initial rate of fusion was proportional to the amount of alpha-tocopherol present in the bilayer. An alpha-tocopherol concentration-dependent decrease of both the initial rate and the final extent of release of vesicle contents was also observed. This effect was more evident as more alpha-tocopherol was incorporated in the bilayer, so that in the presence of 10 mol% of alpha-tocopherol no significant release was observed after 5 min. The stabilization of the vesicular structure exerted by alpha-tocopherol was responsible for the apparent increase of the fluorescence intensity of the Tb-DPA complex at later stages of the process. The results reflect a perturbation of the membrane by low concentrations of alpha-tocopherol which may account for a number of biological effects of this vitamin, not related to its antioxidant role.
已研究了α-生育酚对Ca(2+)诱导的大单室磷脂酰丝氨酸囊泡融合的影响。用铽-二吡啶甲酸（Tb-DPA）分析法持续监测水相囊泡内容物的混合情况，同时将预先包封的Tb-DPA复合物的解离作为囊泡内容物释放的指标。在不同Ca2+浓度下使用由纯磷脂酰丝氨酸以及含有2%、5%和10%摩尔分数α-生育酚的磷脂酰丝氨酸组成的囊泡。低含量α-生育酚的存在降低了融合的初始速率，而未改变Ca2+阈值浓度。融合初始速率的降低与双层中α-生育酚的含量成正比。还观察到囊泡内容物释放的初始速率和最终程度均随α-生育酚浓度降低。随着双层中掺入更多α-生育酚，这种效应更明显，因此在存在10%摩尔分数α-生育酚的情况下，5分钟后未观察到明显释放。α-生育酚对囊泡结构的稳定作用导致了在该过程后期Tb-DPA复合物荧光强度的明显增加。结果反映了低浓度α-生育酚对膜的扰动，这可能解释了该维生素的许多生物学效应，与其抗氧化作用无关。
