INTRAMOLECULAR DONOR‐ACCEPTOR SEPARATIONS IN METHIONINE‐ AND LEUCINE‐ENKEPHALIN ESTIMATED BY LONG‐RANGE RADIATIONLESS TRANSFER OF SINGLET EXCITATION ENERGY

The Förster theory of radiationless electronic excitation energy transfer was used to determine the intramolecular separation between the tyrosine and phenylalanine residues in leucine‐ and methionine‐enkephalin. The spectral overlap integrals and the Förster critical distances were evaluated. Transfer efficiencies were determined by observing sensitized fluorescence of the acceptor and quenching of the donor fluorescence. The results were compared with theoretical estimations, better agreement being obtained with the first method.