UV RESONANCE RAMAN AND ABSORPTION STUDIES OF ANGIOTENSIN-II CONFORMATION IN LIPID ENVIRONMENTS

We have used UV resonance Raman and absorption spectroscopy to examine the secondary structure of angiotensin II (AII) in aqueous solution a nd in phospholipid micelles. Absorption difference spectroscopic measu rements are used to determine the association constant of AII with dod ecylphosphocholine (DPC) micelles, and the UV Raman spectral data are used to examine the secondary structure alterations which occur upon A II partitioning into the DPC micelles. The 208 nm excited amide III pe ptide bands give information on the peptide backbone conformation. AII appears to exist in several conformers such as beta-sheet, irregular, and turnlike structure in aqueous solution, while it adopts a more hi ghly ordered beta-turn structure in DPC micelles. The Tyr and Phe abso rption and Raman excitation profile redshifts upon AII binding to DPC micelles indicate that the Tyr and Phe side chains of AII, which are e xposed to water in aqueous solution, partition into the hydrophobic co re of the lipid DPC micelles. (C) 1996 John Wiley & Sons, Inc.