Dimerization kinetics of violamycin BI anthracycline - the influence of ionic strength

Violamycin BI is an anthracycline derivative with two sugars hanging on, ea ch of them carries one positive charge. It dimerizes under conditions, whic h depend on the concentration of the antibiotic, pH and the ionic strength of the solution. By keeping a constant pH in a phosphate-EDTA buffer, the r ate constants of violamycin BI dimerization were determined at various ioni c strengths by temperature jump method. The dimerization constant K-d, resu lting from the ratio of these rate constants, confirmed the values obtained spectrophotometrically in this study or elsewhere. The influence of ionic strength (0.02-0.2 hi) on the rate constant values suggested to us some spe culations on the reaction mechanism of the dimerization, in which, the spec ific mutual orientation of the monomers in the encounter, and perhaps a spe cific conformation of their side groups is required before a stabilizing ac tion of the binding forces sets in. (C) 2000 Elsevier Science B.V. All righ ts reserved.