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Influence of solvents and leucine configuration at position 5 on tryptophan fluorescence in cyclic enkephalin analogues
Author(s) -
Malicka Joanna,
Groth Małgorzata,
Karolczak Jerzy,
Czaplewski Cezary,
Liwo Adam,
Wiczk Wiesław
Publication year - 2001
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/1097-0282(20010405)58:4<447::aid-bip1020>3.0.co;2-4
Subject(s) - chemistry , tryptophan , conformational isomerism , acetonitrile , residue (chemistry) , fluorescence , solvent , solvent effects , stereochemistry , organic chemistry , amino acid , molecule , biochemistry , physics , quantum mechanics
The fluorescence decay of tryptophan is a sensitive indicator of its local environment within a peptide or protein. In this study we carried out fluorescence measurements of the tryptophan residue of cyclic enkephalin analogues of a general formula X–c[ D ‐Dab 2 –Gly 3 –Trp 4 –Y 5 ] where X = Cbz or H and Y = D ‐ or L ‐Leu, in four solvents [water, methanol, acetonitrile, and dimethyl sulfoxide (DMSO)]. An analysis of the tryptophan fluorescence decays using a discrete‐exponential model indicates that tryptophan fluorescence decay can be described by a double exponential function in all solvents studied. Lifetime distribution analysis yields a bimodal distribution in protic solvents (water and methanol), whereas an asymmetric, unimodal distribution in an aprotic solvent (DMSO) and uni‐ or bimodal distributions in acetonitrile solution, depending on leucine configuration. The data are interpreted in terms of the rotamer model, in which the modality and the relative proportions of the lifetime components are related to the population distribution of tryptophan χ 1 rotamers about the C α C β bond. The chirality of the Leu 5 residue and solvent properties affect the local environment of the tryptophan residue and therefore influence the distribution of side‐chain rotamers. These results are consistent with the results of theoretical conformational calculations. © 2001 John Wiley & Sons, Inc. Biopolymers 58: 447–457, 2001