A study of the interaction of some neuropeptides and their analogs with bilayer lipid membranes and liposomes

Abstract

Several biophysical methods have been used to study the interaction of the amphiphilic hormone derivative ACTH t-24, the wasp venom peptide mastoparan and the synthetic neuropeptide galparan with planar bilayer lipid membranes (BLM) and liposomes. Addition of ACTH 1–24, galparan and mastoparan at different concentrations (0.1 μM to 0.1 mM) to BLM from soybean phosphatidylcholine leads to an increase of membrane electrical conductance to an extent that correlates with the activity of the different peptides on mast cells. Addition of ACTH 1–24 to a suspension of DMPC + DMPG liposomes leads to an increase of dielectric relaxation time, however the less charged peptides did not influence the dielectric relaxation properties of liposomes. The velocity number [ u], measured by ultrasonic velocimetry in suspensions of liposomes from DMPC, decreased after addition of the peptides. This reveals an increase of the adiabatic volume compressibility of the liposomes. The presence of ACTH 1–24, galparan and mastoparan in liposomes of DMPC (mole fraction peptide/DMPC=7.7 × 10 −4) resulted in different changes of absorption number Δ[αλ] of ultrasound at temperatures below and above the phase transition of DMPC. The results obtained are consistent with the idea that the lipid bilayer may function as a mediator for the receptor-independent stimulation of G-proteins.