Folding of a peptide corresponding to the .alpha.-helix in bovine pancreatic trypsin inhibitor

A short peptide corresponding to the alpha-helical region of BPTI shows partial folding in aqueous solution (pH 7) as judged by circular dichroism (CD). Folding is temperature and denaturant sensitive, and the peptide is monomeric. The difference CD spectrum, obtained from spectra at two temperatures, indicates that the peptide folds as an alpha-helix. Difference CD spectroscopy provides a sensitive assay for helix formation in peptides exhibiting small amounts of structure. Helix stability in this peptide shows a marked pH dependence which is consistent with stabilizing charged side-chain interactions with the helix dipole and/or salt bridge formation.