Energy of interaction in actinomycin-nucleotide complexes

Complexes of the natural heterocyclic antibiotic actinomycin D (AMD) with its putative carriers: purine and pyrimidine nucleotides, as well as with fragmented DNA and phospholipid liposomes have been studied by high-sensitivity spectrophotometry. The antibiotic is not only adsorbed onto the surface of purine clusters but also is incorporated into them. It is especially readily incorporated into unwound DNA regions. The incorporation is accompanied by a long-wavelength shift of the absorption spectrum. From the magnitude of the shift, the energy of interaction was calculated. In the case of AMD in the complex with caffeine and adenosine, it is 2.4 and 2.7 kcal/mol, and in the complex with guanosine and fragmented DNA it is considerably higher, 3.3 and 3.7 kcal/mol. It is assumed that guanosine, adenosine, caffeine and fragmented DNA may serve as carriers of the antibiotic.