Proton exchange kinetics in [d(ACGTATACGT)]2-echinomycin and [d(ACGTTAACGT)]2-echinomycin complexes.

Based on imino proton exchange catalysis, base-pair lifetimes and apparent dissociation constants are reported on the complexes formed by bisintercalation of echinomycin at the CpG steps of the d(ACGTATACGT)2 and d(ACGTTAACGT)2 duplexes. The lifetimes of the four central A x T base pairs between two echinomycin binding sites are much shorter than in the free duplexes. The destabilization of base pairs adjacent to the binding sites is propagated one additional base pair away from the binding site.