[Reaction of fluorescent labeled analogs of the antibiotic distamycin A with synthetic polydeoxyribonucleotides]

Interaction of DNA with the analogs of the antibiotic distamycin A having different numbers of pyrrolcarboxamide units and labeled with dansyl was studied. The intensity of fluorescence of these analogs increases markedly when they bind to DNA. It is shown that the introduction of dansyl into the analog molecules does not change their binding characteristics. The binding isotherms of the analogs to synthetic polydeoxyribonucleotides were obtained. Analysis of the experimental data leads to the following conclusions: 1. The free energy of binding of the analogs to poly(dA1 . poly(dT) depends linearly on the number of pyrrolcarboxamide units in the molecule of the analog whereas attachment of each pyrrolcarboxamide unit produces change of 2 kcal/mole in the free energy. 2. Attachment of a pyrrolcarboxamide unit to GC pair results in the free energy change of 0.95 kcal/mole. 3. Adenine and thymine are close but not equivalent by the energy of binding to the analogs of distamycin A. 4. The binding of analogs to poly(dA . poly(dT) is a cooperative process, presumably dependent on the conformational changes induced by the binding of analogs to DNA.