Fluorospectrometric studies on neothramycin and its reaction with DNA.

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Abstract
The characteristics of neothramycin and its reaction mechanism with DNA were studied by fluorescence spectroscopy. The fluorescence intensity of neothramycin is enhanced by the reaction with DNA. The reaction rate of the drug and DNA is rather slow; and is dependent upon both DNA and drug concentrations, and is stimulated by hydrogen ion. Analysis of the equilibrium reaction suggested that neothramycin possesses about one binding site per 2-3 base-pairs with homogeneous affinity and association constant of 4.7×103 M-1; and no significant mutual interference of the binding sites seems to exist. From the results of neothramycin's interaction with various polynucleotides, it was suggested that a guanine base and a double helix conformation of DNA are required for binding the antibiotic. The current results and previous ones, concerning neothramycin-2'-deoxyguanosine adduct formation, suggested that the antibiotic reacts with 2-amino group of guanine base of DNA by dehydration in the manner of a bimolecular (Sn2ca) equilibrium reaction.