AMINO GROUPS AT SURFACES OF PHOSPHOLIPID VESICLES

Reactivity of the amino groups of three nitrogen-containing phospholipids dispersed in aqueous salt solution in the form of liquid crystalline vesicles was studied by microelectrophoresis. The reactivity against 2,4,6-trinitrobenzenesulfonic acid (TNBS) and formaldehyde after incubation was assessed on the basis of changes in their electrophoretic mobility. It was found that pure phosphatidylethanolamine did not react with TNBS but rather with formaldehyde. If phosphatidylethanolamine was mixed with phosphatidylcholine, which was not reactive alone, with either reagent, the reactivity of phosphatidylethanolamine with both TNBS and formaldehyde was greatly enhanced. It was also found that phosphatidylserine had limited reactivity with either reagent, whether in pure form or in mixtures with phospatidylcholine. It was concluded that the limited reactivity of the primary amino groups at the surface of phospholipid liquid crystalline vesicles dispersed in saline is due to inter- and intramolecular salt linkages with adjacent phosphate groups. The effect of ΔpH at the surface is also discussed as a possible explanation for the lack of reactivity. Finally the implications of these findings are discussed in terms of some of the proposed models for biological cell membrane structure. © 1969.