AbstractTwo studies are diescribed in which synthetic peptides have been designed and examined to address biochemical problems inherent in hydorphobic environments: (1) The cyclic hexapeptide cyclo‐(D‐Tyr(Bzl)‐Gly‐Ile‐Leu‐Gln‐Pro) was synthesized as a model of an interior β‐turn from the protein lysozyme. Conformational analysis by proton nmr methods, including two‐dimensional nulcear Overhauser effect spectroscopy, revealed that the model peptide adopts one conformation in chloroform/dimethyl sulfoxide (98.2) and tetramethylene sulfone solutions. The conformation consists of two linked β‐turns, one with the same sequence (Gly‐Ile‐Leu‐Gln) and geometry (Type I) as the protein turn. (2) Major portions of the λ‐receptor protein (LamB) signal sequences fromE. coliwildtype and mutant strains have been synthesized. The conformational properties and membrane interactions of these synthetic signal peptides correlate with thein vivoexport function of the wild type and mutant strains. Functional signal sequences are significantly richer in α‐helix in aaqueous trifluoroethanol, lysolecithin, or sodium do‐decyl sulfate solution than is a n