Abstract:
The human a-tocopherol transfer protein (h-a-TTP) is understood to be the entity
responsible for the specific retention of a-tocopherol (a-toc) in human tissues over all
other forms of vitamin E obtained from the diet. a-Tocopherol is the most biologically
active form of vitamin E, and to date has been studied extensively with regard to its
antioxidant properties and its role of terminating membrane lipid peroxidation chain
reactions. However, information surrounding the distribution of a-tocopherol,
specifically its delivery to intracellular membranes by a-TTP, is still unclear and the
molecular factors influencing transfer remain elusive. To investigate the mechanism of
ligand transfer by the h-a-TTP, a fluorescent analogue of a-toc has been used in the
development of a fluorescence resonance energy transfer (FRET) assay.
(/?)-2,5,7,8-tetramethyl-2-[9-(7-nitro-benzo[l,2,5]oxdiazol-4-ylamino)-nonyl]-
chroman-6-ol (NBD-toc) has allowed for the development of the FRET-based ligand
transfer assay. This ligand has been utilized in a series of experiments where changes
were made to acceptor lipid membrane concentration and composition, as well as to the
ionic strength and viscosity of the buffer medium. Such changes have yielded evidence
supporting a collisional mechanism of ligand transfer by a-TTP, and have brought to
light a new line of inquiry pertaining to the nature of the forces governing the collisional
transfer interaction.
Through elucidation of the transfer mechanism type, a deeper understanding of
the transfer event and the in vivo fate of a-tocopherol have been obtained. Furthermore,
the results presented here allow for a deeper investigation of the forces controlling the
collisional protein-membrane interaction and their effect on the transfer of a-toc to
membranes. Future investigation in this direction will raise the possibility of a complete
understanding of the molecular events surrounding the distribution of a-toc within the
cell and to the body's tissues.
