SALT EFFECTS ON PEPTIDE CONFORMERS - A DIELECTRIC STUDY OF TUFTSIN

Four 1-ns molecular dynamics computer simulations of tuftsin, Thr-Lys- Pro-Arg, are analyzed: (1) cis tuftsin in water, (2) trans tuftsin in water, (3) cis tuftsin in 1 M NaCl, and (4) trans tuftsin in 1 M NaCl. Independently of the salt concentration, the trans conformer has a hi gher dielectric constant than the cis conformer because the former exh ibits a more widely distributed charge distribution in space. Independ ently of the peptide conformation, the presence of salt reduces the di electric constants of both the peptide and the solvating water molecul es because ions, on binding, restrict the motion of other atoms. In co ntrast to the dielectric constants, neither the peptide conformation n or the salt concentration shows a significant influence on the dielect ric relaxation time of water molecules.