Peptide-Phospholipid Complex Formation at Liquid-Liquid Interfaces

Two peptides known to interact with receptors embedded in cell membranes, angiotensin III (AngIII) and Leuenkephalin(LeuEnk), were studied electrochemically at the interface formed between two immiscible electrolyte solutions modified by an adsorbed monolayer of dipalmitoylphosphatidylcholine(DPPC). The results indicate thatcationic angiotensin III transfer can be facilitated by the interfacial formation of a complex with DPPC. The complexation constant was determined by voltammetry and found to be equal to 5.2 × 104 M-1. For neutral Leuenkephalin, a current only observable in the presence of the lipidic monolayer results from the formation of a complex between the lithium cation, LeuEnk or LeuEnk dimer and the phospholipid. For both peptides, the peptide-lipid complexes were identified by biphasic electrospray ionization mass spectrometry using a setup consisting of a dual-channel microchip, which puts in contact two immiscible phases at the Taylor cone and makes possible the study of interfacial complexes. The stability of the 1:1 complexes between lysine, diphenylalanine, AngIII, and LeuEnk and DPPC were evaluated by varying the temperature of the heated capillary of the mass spectrometer. Finally, from the complementary use of voltammetry and mass spectrometry, a mechanism for the interaction between these two biologically relevant peptides and DPPC monolayers is formulated.