β-Endorphin: Formation of α-helix in lipid solutions

Human β-endorphin adopts a partial helical conformation in aqueous solutions of cerebroside sulfate, ganglioside GM1, phosphatidylserine, and phosphatidic acid, but not of cerebroside and phosphatidylcholine, as evidenced by circular dichroic spectra. Addition of Ca²⁺ to the peptide in cerebroside sulfate solution can break up the helix; at 10 mM Ca²⁺ the peptide (12 μM) essentially exists in an unordered form. For comparison, sheep β-lipotropin in acidic cerebroside sulfate solution (pH < 4) also has a partial helical conformation, whereas human adrenocorticotropin does not. The conformation of the complex between human β-endorphin and lipids may be related to the opiatelike function of this peptide hormone.