[Binding of actinomycin D analogs to DNA]

Equilibrium and kinetic studies are reported on the binding to DNA of actinomycin D analogues containing various substituents at position 7 of the antibiotic chromophore. The binding constants are calculated from the experimental binding isotherms of actinomycin D and its analogues to calf thymus DNA. The rate constants of the association and dissociation processes are measured by stop -- flow method. From these experiments a conclusion is drawn that small substituents (such as nitro or aminogroups) at position 7 of the actinomycin chromophore exhibit a little (if any) influence both on the affinity of antibiotic for DNA and kinetics of association and dissociation processes, while bulky substituents decrease the antibiotic binding affinity and make kinetics behavior slower.