The effect of chlorpromazine on some properties DNA in solution

The effect of chlorpromazine [2-chloro-10-(3-dimethylaminopropyl)-phenothiazine] on calf thymus DNA has been investigated by spectrophotometric, equilibrium dialysis, thermal denaturation, sedimentation and viscosity methods. The absorption spectra of DNA undergo two important changes upon binding to chlorpromazine, namely, the displacement of peaks to longer wavelength (ranging from 5-8 nm) and a decrease in the optical density. The extent of binding of chlorpromazine to native calf thymus DNA, AS MEASURED BY SPECTROPHOTOMETRIC METHOD, IS DECREASED WITH INCREASING SODIUM CHLORIDE Concentration. A curvature in the Scatchard plot suggests two types of binding processes. Chlorpromazine decreases the optical density at higher temperatures without affecting the Tm of DNA. In its presence, the absorption spectra of purine deoxynucleosides (dA, dG) and of deoxynucleotides (dAMP, dGMP) are modified, i.e., the maxima are displaced to longer wavelength (ranging from 5-17 nm) and there is a general decrease in the optical density. No such effect is observed with pyrimidine deoxynucleosides (dC, dT) and deoxy-nucleotides (dCMP, dTMP). A combination of electrostatic binding of the amino group of chlorpromazine sidechain with the negative phosphate groups of the DNA and a partial insertion of either of its two phenyl rings between the nucleotide base pairs of the DNA plus the binding caused by mutual interaction between different chlorpromazine molecules at higher concentration is proposed as a probable mode of binding of chlorpromazine to DNA.