Fluorescence studies of endothelin-1

Fluorescence measurements and singlet singlet energy transfer experiments on endothelin-1 provide information on the conformation of this peptide in dilute aqueous solution. The tyrosine fluorescence quantum yield in the absence of transfer (in [Phe(21)]endothelin-1) is relatively large (?(tyr) = 0.39), indicating the side-chain is oriented away from fluorescence quenching groups such as the two disulfide bonds of the peptide. The fluorescence emission maximum (? = 351 nm) and quantum yield (?(trp) = 0.099) of tryptophan in endothelin-I suggests that this residue is fully accessible to the solvent and that the indole ring is not located near the fluorescence quenching histidinium moiety or the disulfide bonds. Singlet-singlet fluorescence energy transfer measurements of the Tyr(13)/Trp(21) intramolecular distance by both donor fluorescence quenching and relative enhancement of acceptor fluorescence yield a distance of about 12.8 +/- 0.6 A ? . Molecular modeling of a fully extended C-terminal hexapeptide indicates a Tyr(13)/Trp(21) distance of about 25 A. Thus, the C-terminal residues must bend back towards the bicyclic portion of the molecule.