Degree of DNA Unwinding Caused by the Binding of Aclacinomycin A

概要

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The effect of drug binding on the geometry of DNA duplex (plasmid pBR322) has been examined using topoisomerase I relaxation followed by gel electrophoresis. The binding of one molecule of aclacinomycin A was found to cause an unwinding of the DNA double helix by an angle of 8±2°in aqueous solution at 37℃. The unwinding angle of daunomycin was 12±2°, and that of ethidium bromide 15±3°. To determine the unwinding angle, precise determination of the equilibrium constant of drug-DNA binding-dissociation reaction in the same buffer as that for the topoisomerase reaction (at 37℃) was indispensable. This determination was made by ultraviolet absorption measurement of the same plasmid-drug system, followed by a Scatchard plot and analysis using McGhee-von Hippel's excluded site model. For the aclacinomycin-pBR322 system, the binding constant (K) was 7.2×10^4M^<-1>, and the number of base pairs in the single site of drug binding (n) was 4.0. For daunomycin-pBR322,K=7.1×10^4M^<-1> and n=3.4,and for ethidium-pBR322,K=4.0×10^4M^<-1> and n=3.3. On the basis of these experimental results, the possible role of the sugar moieties of these antitumour drugs, as well as that of intercalating chromophores, was discussed.
公益社団法人日本薬学会の論文
1997-10-15