Properties of hexadecaprenyl monophosphate/dioleoylphosphatidylcholine vesicular lipid bilayers.

Abstract

In our study we investigated hemispherical phospholipid bilayer membranes and phospholipid vesicles made from hexadecaprenyl monophosphate (C(80)-P), dioleoylphosphatidylocholine (DOPC) and their mixtures by voltammetric and transmission electron microscopy (TEM) techniques. The current-voltage characteristics, the membrane conductance-temperature relationships and the membrane breakdown voltage have been measured for different mixtures of C(80)-P/DOPC. The membrane hydrophobic thickness and the activation energy of ion migration across the membrane have been determined. Hexadecaprenyl monophosphate decreased in comparison with DOPC bilayers, the membrane conductance, increased the activation energy and the membrane breakdown voltage for the various value of C(80)-P/DOPC mole ratio, respectively. The TEM micrographs of C(80)-P, DOPC and C(80)-P/DOPC lipid vesicles showed several characteristic structures, which have been described. The data indicate that hexadecaprenyl monophosphate modulates the surface curvature of the membranes by the formation of aggregates in liquid-crystalline phospholipid membranes. We suggest that the dynamics and conformation of hexadecaprenyl monophosphate in membranes depend on the transmembrane electrical potential. The electron micrographs indicate that polyprenyl monophosphates with single isoprenyl chains form lipid vesicular bilayers. The thickness of the bilayer, evaluated from the micrographs, was 11 +/- 1 nm. This property creates possibility of forming primitive bilayer lipid membranes by long single-chain polyprenyl phosphates in abiotic conditions. It can be the next step in understanding the origin of protocells.