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DARK INTERACTION AND OXYGEN DEPENDENT PHOTOBINDING BETWEEN AN AROMATIC TETRAPEPTIDE AND DNA MODIFIED BY 5‐ METHOXYPSORALEN MONOADDUCTS

The binding of the tetrapeptide lysyl‐tryptophyl‐glycyl‐lysine t‐butyl ester to native DNA and DNA photochemically modified by 5‐methoxypsoralen has been investigated by fluorescence spectroscopy. The peptide exhibits a higher affinity for the modified DNA than for the undamaged DNA. This is due to the presence of strong stacking sites in the vicinity of 5‐methoxypsoralen monoadducts. Upon irradiation at 365 nm of the peptide‐modified DNA complexes, a cross‐linking of the peptide to the nucleic acid is observed. This photochemical addition requires the presence of oxygen and involves, in part, singlet oxygen.