INTERACTION OF ADRENOCORTICOTROPIN-(1-24)-TETRACOSAPEPTIDE WITH LIPIDBILAYERS

The interaction of the peptide hormone adrenocorticotropin with solven t-free planar lipid bilayers (BLM) and liposomes was studied by measur ements of elasticity modulus perpendicular to the plane of the membran e (E(perpendicular to), measured by electrostriction), surface potenti al difference (Delta Phi(m)), electrical capacitance, capacitance rela xation following a voltage jump (yielding relaxation times for molecul ar dipoles or dipolar domains), and fluorescence polarization. Additio n of the g-fold positively charged peptide to one side of the membrane leads to a more positive membrane surface potential, an increase of B LM capacitance, a decrease of elasticity modulus, and faster relaxatio n time constants. This also caused a decrease of DPH fluorescence anis otropy of the liposome suspension modified by fluorescent dye DPH. Mix ed BLM of palmitoyl-oleoyl-phosphatidylcholine (POPC) + soybean phosph atidylcholine (SBPC) (10:1 w/w), which carry a negative surface charge , exhibit considerably larger changes than electroneutral POPC membran es. Our results confirm that ACTH(1-24) binds to BLM and interacts wit h the hydrophobic part of the bilayer.