NMR studies on angiotensin II: histidine and phenylalanine ring stacking and biological activity.

The conformations of angiotensin II and the antagonist [Sar1, Ile8]angiotensin II in dimethylsulfoxide have been examined by high resolution proton magnetic resonance spectroscopy at 400 MHz. The chemical shifts for the aromatic protons of the phenylalanine residue in angiotensin II are consistent with shielding and restricted rotation for this side-chain. The chemical shifts for the histidine C2 and C4 protons in angiotensin II also indicate shielding, whereas these same protons in the antagonist [Sar1, Ile8]angiotensin II do not demonstrate this shielding influence. These findings suggest a stacking interaction for the histidine and phenylalanine side-chains in angiotensin II which is important for activating angiotensin receptors.