Circular-dichroism spectra of truncated and other analogs of angiotensin II.

Circular dichroism spectra on angiotensin II and analogs, and its truncated N-terminal and C-terminal peptides were determined in fluroinated alcohols under several conditions in the peptide or aromatic spectral regions. The following conclusions were suggested: (a) evidence for a beta structure for angiotensin II; (b) evidence for a folding at the N-terminal and C-terminal part of the molecule; (c) an interaction involving the C-terminal residue which decreases progressively when phenylalanine is replaced by isoleucine and then by alanine; (d) the N-terminal amino acid seems to play an important role in the overall conformation of the molecule possibly by interacting with the C-terminus, its absence in the 2 -- 8 heptapeptide giving rise to a more pronounced signal than angiotensin II; (e) in trifluoroethanol the conformation of these peptides is well defined and fits well with observed structure-activity relationships and observed binding data. There is a loss of this relationship when these solvents are diluted with water.