MOLECULAR DISTORTION OF DISTAMYCIN ON BINDING TO DNA AS REVEALED BY RAMAN-SPECTROSCOPY

The Raman spectra of distamycin and its complex with DNA were examined in both H2O and D2O solutions. To facilitate band assignments, Raman spectra of several small model compounds of distamycin were also obtained. On binding to DNA, the CO stretching band at 1620 cm−1 (amide I band) of distamycin was shifted upwards by 14 cm−1, whereas a strong pyrrole‐ring stretching band at 1437 cm−1 was shifted downwards by 7 cm−1 in H2O. In addition, most of the Raman bands including amide I, II and III became narrower and sharper on binding to DNA. These results indicate that, in the free state, the dihedral angles around the CC and NC bonds connecting the pyrrole ring and the peptide chain of distamycin fluctuate near 0° (coplanar configruation), whereas in the bound state these angles are fixed and markedly shifted from 0°. Previous x‐ray and NMR studies on distamycin (netropsin)–DNA complexes show that such deviations occur when these drug molecules are bound in the minor groove of DNA. Molecular distortion of distamycin caused by interaction with other polynucleotides has also been elucidated by using such spectral characteristics as diagnosis. Copyright © 1990 John Wiley & Sons, Ltd.