NMR-TITRATIONS WITH COMPLEXES BETWEEN DS-DNA AND INDOLE-DERIVATIVES INCLUDING TRYPTOPHANE CONTAINING PEPTIDES

It is shown that NMR titrations can be used on a quantitative basis to derive binding constants and binding modes of ds-DNA ligand complexes from several signals. The results are partially at variance with lite rature conclusions; they can be interpreted by additive and independen t contributions of electrostatic interactions between DNA phosphate an d ammonium centers in the side chain of the ligands, and of very weak stacking contributions of the indole rings. While gramine and tryptami ne are found to intercalate, tryptophane-containing peptides do so onl y, if the tryptophane is flanked by at least two lysine units.