Influence of alpha-tocopherol incorporation on Ca(2+)-induced fusion of phosphatidylserine vesicles.
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.
Aranda
F J
FJ
Departamento de Bioquímica y Biología Molecular A, Facultad de Veterinaria, Universidad de Murcia, Spain.
Sánchez-Migallón
M P
MP
Gómez-Fernández
J C
JC
D002118:Calcium; D007700:Kinetics; D008081:Liposomes; D008561:Membrane Fusion; D008954:Models, Biological; D010718:Phosphatidylserines; D010848:Picolinic Acids; D013725:Terbium; D014810:Vitamin E
D008081:Liposomes; D010718:Phosphatidylserines; D010848:Picolinic Acids; D013725:Terbium; D014810:Vitamin E; D002118:Calcium; C004860:dipicolinic acid