The tyrosyl fluorescence of angiotensin II in alcoholic solvents

Angiotensin II is an octapeptide hormone and contains a single tyrosyl residue and no tryptophyl residues. Intramolecular interactions of the tyrosyl residue with, for example, ionizable side chains or hydrogen bond acceptors can potentially perturb its fluorescence properties. The intrinsic fluorescence of angiotensin II was used to determine if the interactions of the tyrosyl residue were altered, as a consequence of conformational changes induced by certain alcoholic solvents. Steady state and time-resolved fluorescence data for angiotensin II in neutral aqueous buffer, isopropanol and 1,2=propanediol, provided no evidence for specific conformations, which facilitated intramolecular association of the tyrosyl residue with other moieties. Multiexponential decay kinetics in which the decay times were <5 ns were observed in all cases. No fluorescence which could be attributed to tyrosinate anion was detected in the solvent systems studied.