Influence of phospholipid composition on the properties of reconstituted surfactants

The influence of phospholipids on the ultrastructure and metabolism of reconstituted surfactants has not been well defined. The aim of this study was to determine if changes in the phospholipid composition of reconstituted surfactants altered their biophysical properties, ultrastructure, and conversion to light subtype by cycling. We prepared various surfactants containing radiolabeled dipalmitoylphosphatidylcholine ([14C]DPPC). The addition of phosphatidylglycerol (PG) or dipalmitoylphosphatidic acid (PA) to DPPC increased conversion to light subtype. In contrast, the addition of dipalmitoylphosphatidylglycerol (DPPG) to DPPC markedly reduced conversion to light subtype on cycling. DPPC and DPPC+PG produced large liposomes ( approximately 1,000 nm), whereas DPPC+PA or DPPC+DPPG formed multilamellar membranes. Mixtures of DPPC and PA were highly surface active in vitro, whereas the surface activity of DPPC+DPPG was similar to that of DPPC. In conclusion, the ultrastructure, metabolism, and surface active properties of DPPC+PG mixtures were influenced markedly by alterations in the fatty acid composition or polar head group of PG.