COMPARATIVE STUDY OF THE INTERACTION BETWEEN SYNTHETIC METHIONINE-ENKEPHALIN AND MONOLAYERS OF ZWITTERIONIC AND NEGATIVELY CHARGED PHOSPHOLIPIDS

Using Langmuir's monolayer technique, surface behaviour and the interaction between a synthetic analogue of endogenous neuropeptide Methionine-enkephalin (Met-enk) and zwitterionic dimyristoylphosphatidylcholine (DMPC), and the negatively charged dimyristoylphosphatidylglycerol (DMPG) at air/water interface are studied. By using the Wilhelmy method, surface tension (gamma, mN/m) changes (after injection of the peptide under the interface) of DMPG and DMPC monolayers as a function of time at given molecular area are detected. The decrease in gamma values shows that there is a strong penetration effect of Met-enk molecules into the monolayers. The comparison of the interaction between the hydrophobic pentapeptide and both phospholipid monolayers shows that the enkephalin interacts similarly with DMPG and DMPC molecules, and that the ability of Met-enk to penetrate correlates with the given surface area per lipid molecule. Based on the results obtained we suggest that in case of liquid-expanded monolayers the electrostatic attraction facilitates the interaction between the neuropeptide and the negatively charged phospholipids (DMPG), while at more compact ordering of lipid molecules the penetration of the enkephalin is preliminary due to hydrophobic interactions.