Interaction of plasma high density lipoprotein HDL2b (d 1.063–1.100 g/ml) with single-bilayer liposomes of dimyristoylphosphatidylcholine

Incubation of a major subfraction, HDL_2b (d 1.063–1.100 g/ml), of human plasma high density lipoproteins, HDL (d 1.063–1.21 g/ml), with single-bilayer liposomes of dimyristoylphosphatidylcholine (DMPC) resulted in uptake of DMPC by the HDL_2b and dissociation of lipid-free apolipoprotein A-I (apoA-I). In the presence of excess DMPC, the dissociated apoA-I was also incorporated with DMPC into discoidal complexes. Preliminary studies with model apoA-I-DMPC complexes indicated that they also can interact with native HDL_2b with the resultant transfer of their DMPC to HDL_2b and the concomitant release of their apoA-I. After interaction of HDL_2b with DMPC liposomes, the DMPC-enriched HDL_2b product showed a lower hydrated density and a larger particle size than the control HDL_2b. The molecular properties of the lipoprotein product suggest that stabilization of the apoA-I-depleted HDL_2b probably occurred via substitution of DMPC for the apoA-I at the HDL_2b surface rather than by fusion of the apoA-I-depleted HDL_2b. The above interactions of HDL_2b with single-bilayer liposomes and discoidal complexes indicate pathways of phospholipid transfer relevant to the possible role of HDL in the metabolism of lipoprotein surface components in vivo.