Net Transfer of Phosphatidylcholine From Plasma Low Density Lipoproteins to Sphingomyelin-Apoliporotein Complexes by Bovine Liver and Human Plasma Phospholipid Exchange Proteins

Abstract

Bovine liver phosphatidy1cho1ine exchange protein facilitated the net transfer of [14C]dipa1mitoy1 phosphatidy1cho1ine from radio1abeled low density lipoproteins (LDL) to complexes of sphingomyelin and apolipoprotein A-II (apoA-II). Transfer of the radiolabe1ed phosphatidylcholine was dependent on temperature and incubation time, as well as the ratio of LDL to sphingomye1inapoA- II. When unlabeled LDL was incubated with sphingomyelinapoA- II complex containing [14C] sphingomyelin, negligible amounts of the radiolabe1 were transferred to the LDL, implying that the transfer of phosphatidy1cho1ine to the sphingomye1in-apoA-II complex was not coupled with a return of sphingomyelin to the LDL. Bovine liver phosphatidylcholine exchange protein also facilitated the net transfer of [14C]dipa1mitoy1 phosphatidylcho1ine from sonicated vesicles of l-pa1mitoyl-2-palmitoleoyl phosphatidy1choline to sphingomyelin-apoA-II complex. Dansy1 phosphatidylethanolamine incorporated in the donor vesicles was not transferred to the sphingomyelin-apoA-II complex, indicating that phospholipid transfer was not due to a disruption of the vesic1es" and subsequent fusion of vesicle remnants with the sphingomyelin-apoA-II complex. Bovine liver phosphatidylcholine exchange protein did not transfer [14C]- dipalmitoyl phosphatidylcholine or [3 H] cholesteryl esters from high density lipoproteins (HDL) to sonicated vesicles of sphingomyelin. Fluorescence polarization studies showed that relative to the sphingomyelin-apoA-II complexes, the sphingomyelin vesicles have a rigid structure which may account for this lack of transfer of the [l4C]phosphatidylcholine.Phospholipid exchange protein(s) isolated from human plasma also facilitated the net transfer of [l4C]dipalmitoyl phosphatidylcholine from LDL to sphingomyelin-apoA-II complexes.