Interaction of anthracycline antibiotics with biopolymers: Comparative studies of DNA binding and antimicrobial activity of rhodomycin-type anthracycline antibiotics

The binding of the anthracyclines β-rhodomycin-I and β-rhodomycin-II to calf thymus DNA was investigated by both equilibrium and kinetic methods taking into account ligand dimerization (ionic strength I = 0.2 M, pH 6.0). The analysis was based upon a cooperative single-step binding mechanism with overlapping of potential binding sites on a linear homogeneous lattice. Equilibrium binding parameters were estimated from spectrophotometric titration experiments by means of a nonlinear fitting program. The results were compared with those obtained previously for the related antibiotic iremycin and were complemented by kinetic parameters determined from temperature-jump experiments at high binding ratio. The binding constants and the mean attachment times of the drugs were found to increase in the serial order iremycin, β-rhodomycin-I and β-rhodomycin-II, which is in line with their increasing antimicrobial activity on Bacillus subtilis ATCC 6633.