In vitro interaction of opioid peptides with phospholipids. Formation and characterization of complexes

In vitro interactions of opioid peptides with phospholipids. II. Additional spectral evidence

The interaction of leu-enkephalin with phosphatidylserine has been studied with ultraviolet and circular dichroism spectroscopy methods as well as with fluorescence anisotropy techniques. The data reported hereunder confirm the existence of binding between the two species, and also support the hypothesis that not only the tyrosine, but also the phenylalanine residue in the leu-enkephalin molecule is involved in peptide-lipid interaction. In addition, ultraviolet and CD evidence, taken together, tend to suggest that both aromatic residues are bound, with a different degree of involvement, to the same region of the lipid molecule. The data reported are discussed in terms of the interaction model previously proposed by us.

In vitro interaction of opioid peptides with phospholipids. III. The role of lipid

The binding of tritiated Leu-enkephalin to phosphatidylserine and phosphatidylcholine vesicles, both unmodified and modified by the incorporation of free fatty acid, has been studied by steric exclusion chromatography, ultraviolet difference spectroscopy and fluorescence anisotropy. The results obtained tend to confirm that both ionic and hydrophobic interactions are important in the binding phenomena. On the other hand, it seems likely that steric factors play a very limited role in the recognition of the phospholipid by the opioid peptide. Finally, these results confirm the existence of three complexes of different size, as already demonstrated. But, unlike the previously presented results, they stress the importance of the larger of the three complexes formed through binding.