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Department of Biophysical Chemistry, Biocenter, University of Basel, CH-4056 Basel, Switzerland Received December 15, 1986; Revised Manuscript Received March 5, 1987 abstract: The secondary structure of alamethicin in lipid membranes belowand above the lipid phase transition temperature Tt is determined by Raman spectroscopy and circular dichroism (CD) measurements. In both cases structural data are obtained by fitting the experimental spectra by a superposition of the spectra of 15 reference proteins of known three-dimensional structure. According to the Raman experiments, in a lipid bilayer above Tt alamethicin is helical from residue 1 to 12, whereas below Tt the helix extends from residue 1 to 16. The remaining C-terminal part is nonhelical up to the end residue 20 both above and below Tt. A considerable lower helix content is derived from CD, namely, 38% and 46% above and below Tt …