Abstract

The conformation of synthetic β-endorphin fragments in cerebroside sulfate solutions was studied by circular dichroism. The lipid was solubilized by the inert nonionic surfactant cetylpoly(oxyethylene) ether to facilitate optical measurements. All peptides show an aperiodic conformation in water. Addition of cerebroside sulfate induces a partial helical structure for human peptides, β_h-endorphin(14-31), (17-31), and (1-5)-(16-31), and porcine peptides, β_p-endorphin(1-25) and (6-31), but α-endorphin, γ-endorphin, and β_h-endorphin(1-19), (6-17), (22-31), and (26-31) remain unordered in the lipid solution. Thus, the helical segment in , β-endorphin is deduced to be in the middle region of the parent molecule, probably involving two to three helical turns of approximately eight to nine amino acid residues between residues 13 and 24. This helical segment may bring the active sites of the otherwise flexible polypeptide to a correct geometry in the lipid environment in order to express its biological activity.