Circular-Dichroism Spectra of Truncated and Other Analogs of Angiotensin II

Abstract
Circular dichroism spectra on angiotensin II and analogs, and its truncated N-terminal and C-terminal peptides were determined in fluorinated alcohols under several conditions in the peptide or aromatic spectral regions. The following conclusions were suggested : (a) evidence for a β 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 weil defmed and fits weil with observed structure-activity relationships and observed binding data. There is a loss of this relationship when these solvents are diluted wich water.