N-NBD-L-alpha-dilauroylphosphatidylethanolamine. A new fluorescent probe to study spontaneous lipid transfer.

Migration of the fluorescent phospholipid N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-L-alpha-dilauroylphosphati dylethanolamine between small sonicated egg phosphatidylcholine vesicles was studied by use of the fluorescence resonance energy transfer method. Contrary to the results of lipid transfer experiments reported for acyl chain NBD-labeled phospholipids (Nichols, J.W. and Pagano, R.E. (1982) Biochemistry 21, 1720-1728), the migration kinetics of N-NBD-DLPE had to be described by a sum of two exponential functions. The fast component (t1/2 approximately equal to 38 min) was assigned to lipid transfer via soluble monomers and the slow component (t1/2 approximately equal to 400 min) to transbilayer motion. A reversible four-stage process is suggested as a kinetic model. Mathematical treatment of this scheme is given yielding an analytical expression for the time dependence of NBD emission intensity. The use of N-NBD-DLPE in the resonance energy transfer measurements offers the advantage of simple chemical synthesis of the fluorescent probe and leads to additional information on transbilayer motion which was not available with the NBD-labeled lipids used so far.