Interaction between antitumor antibiotic chromomycin A3 and Mg2+. I. Evidence for the formation of two types of chromomycin A3-Mg2+ complexes.
Chromomycin A3 (CHRA3) is an antitumor antibiotic which binds to Mg2+. In the present communication, we show, by means of equilibrium spectroscopic studies (such as absorption, fluorescence and circular dichroism), that two types of CHRA3-Mg2+ complexes (of 1:1 and 1.9:1 stoichiometries in terms of CHRA3:Mg2+, respectively) are formed depending on the concentrations of CHRA3 and Mg2+. The rate constant and activation energy for the formation of two complexes are different, thereby reinforcing the proposition that they are different molecular species. This observation is novel and significant in order to understand the anticancer property of the drug. It also provides explanation for earlier observations that site, affinity parameters and mode of interaction of the drug with DNA in the presence of Mg2+ depend on the relative concentration of Mg2+.
Aich
P
P
Biophysics Division, Saha Institute of Nuclear Physics, Calcutta, India.
Sen
R
R
Dasgupta
D
D
D014128:Chromomycin A3 / Q000378:metabolism* / Q000494:pharmacology; D005470:Fluorometry; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D055095:Optics and Photonics; D013053:Spectrophotometry / Q000379:methods
D014128:Chromomycin A3; D008274:Magnesium