Vectorial properties of small vesicles

Abstract

31P-NMR spectra of suspensions of small phospholipidic vesicles (SUVs) often give two peaks, assigned to the outside and inside leaflets of the membranes. We now show that SUVs formed from polyprenyl phosphates, postulated as 'primitive' membranes, can exhibit this phenomenon. At pH 7.35, stable SUVs could not be obtained from phytanyl phosphate, as vesicles spontaneously grew too much. Phytanyl phosphate + 5 mol% phytanol produced stable SUVs at the same pH, in which, however, 31P-NMR showed a single symmetrical peak. At pH 8.9, where dianion phosphates are predominant (they may occupy principally the outer leaflet), 31P-NMR showed two signals of the phosphate both in phytanyl phosphate and phytanyl phosphate/5 mol% phytanol SUVs. This asymmetry of the membrane implies a difference in the ionisation state of the phosphate groups on both sides of the membrane. The resulting gradient of electrochemical properties implies the presence of vectorial properties, a factor that may lead to the 'self-complexification' of these vesicles towards proto-cells.