The reaction of anthramycin with DNA. II. Studies of kinetics and mechanism

Abstract

Anthramycin is known to react firmly with DNA, but no chemical basis for this interaction has been elucidated. Since anthramycin readily undergoes hydrolytic changes at C-11, the possible relation of this reaction to the interaction with DNA was considered. Both the hydrolysis of an 11-methoxy group and the reaction with DNA were found to be H+ catalysed, thus supporting a relation between the two processes. The titration of H+ from the phenolic group at Position 9 of anthramycin was found to be absent in the DNA complex, suggesting that Position 9 also is involved in the complex. The rate of reaction of anthramycin-11-methyl ether with DNA was found to be increased by prior hydrolysis. The rate of reaction with DNA, however, does not involve a rate-limiting conversion of anthramycin to a reactive component, since the kinetics of the reaction were found to be basically bimolecular. This excluded the possibility that a slow conformational change of the DNA was rate-limiting. The findings support the proposal that the binding of anthramycin to DNA is covalent, and that Positions 11 and 9 are involved in the binding. The bimolecular rate constant was found to decrease exponentially with the extent of DNA reaction, probably due to neighboring-site exclusion effects. The site of reaction involves guanine, since only guanine-containing deoxypolynucleotides were found to be reactive, and since reaction of DNA with anthramycin caused stochiometric elimination of binding sites of actinomycin. © 1974.