The effect of sodium bisulfite on the melting profiles of nucleic acids and on their respective nucleosides.

The effect of sodium bisulfite (0.27 M, pH 7) on melting behavior of DNA, yeast RNA and their respective nucleosides was studied. It was found that bisulfite added not only to pyrimidine bases but also to purine bases of nucleic acids and of nucleosides. The addition products were stable at higher temperatures but reverted to parent compounds at room temperature. The only exception was the addition product of uridine which was stable at room temperature and could be isolated by paper chromatography in a 42-62% yield. Heating of DNA solutions in the presence of bisulfite to 95 degrees C caused a 90% loss of absorbance at 260 nm. On cooling, the absorbance was essentially recovered. When compared to the melting behavior of DNA in 0.27 M NaCl or 0.09 M Na2SO4 (same ionic strength), it was found that bisulfite destabilized double helical structure of DNA and that reversible addition of bisulfite did occur much below the melting temperature of DNA observed in the other two solvents.

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.