DETERMINATION OF THE INTRAMOLECULAR TYROSINE-TRYPTOPHAN DISTANCE IN A 7-PEPTIDE RELATED TO THE C-TERMINAL SEQUENCE OF CHOLECYSTOKININ

The solution conformation of a 7‐peptide with the C‐terminal sequence of cholecystokinin was investigated by evaluation of intramolecular resonance energy transfer between tyrosine (donor) in position 1 and tryptophan (acceptor) in position 4. From the relative enhancement of acceptor fluorescence a transfer efficiency of 0.70 ± 0.04 was determined. The use of this parameter in Förster's equation permitted the calculation of the average intramolecular tyrosine‐tryptophan separation, whereby the assumption of random donor‐acceptor orientation was made. The resulting average distance of 10.0 ±0.3 Å suggests some type of a folded conformation and excludes the existence of a fully extended chain in the N‐terminal part of the peptide. A comparison with tyrosine‐tryptophan distances observed in other biologically active polypeptides is made.