Circular dichroism studies on sequential polypeptides (Arg‐X‐Gly) when X = L‐Ala, Val, Leu, Ile, Nva, Nle in amphiphilic environments

A series of (L-Arg-X-Gly)n sequential polypeptides, where X represents the amino acid residues L-Ala, Val, Leu, Ile, Nva, and Nle, have been prepared and their conformational properties as well as their association with nucleic acids in various water fluoroalcohol mixtures have already been reported. In order to gain further insight into the conformational behavior of these polypeptides in amphiphilic environments, we now report their secondary structure, in the presence of increasing amounts of sodium dodecylsulfate and dodecylphosphorylcholine using CD spectroscopy. The CD spectral pattern of all the polypeptides studied is indicative of an equilibrium between α-helix, β-turn, and random coil. They are analyzed in relation to the nature of the X side-chain (length, branching, linearity). The results are explained on the basis of Lundahl's model for polypeptide-micelle interactions.

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