Mus DNA (Sigma, St. Louis, USA) was dissolved in 16 saline sodium

Mus DNA (Sigma, St. Louis, USA) was dissolved in 16 saline sodium citrate (SSC) buffer (0.15 M NaCl and 0.015 M sodium citrate, pH 7.5) as 10 mg solution and left Microcystin-LR overnight at 37uC with occasional vortexing. Constant concentration of DNA (0.343 O.D./absorbance at 260 nm 57773-65-6 biological activity corresponding to <17.2 mg/ml) was maintained for UV absorption studies. On the other hand Herring sperm (HiMedia, Mumbai, India) DNA was used for FTIR (Bruker IFS 66V, Germany) analysis alone. The term drugs used here are with reference to the xanthine derivatives such as theophylline (X1), theobromine (X2) and caffeine (X3) (Sigma, St. Louis, MO, USA).UV absorption spectroscopyFor studying interaction of methylxanthines with native form of DNA or Tm-melted DNA, different aliquots of known concentration of DNA (as mentioned above) was taken in DNase/RNase free microcentrifuge tubes, and the drugs were discretely added at different drug-phosphate (P/D) ratios: 0.8, 1.0, 3.0 6.0. The final volume was made up to 1 ml using 16 SSC buffer. All the samples were incubated overnight at 37uC. Next day, each sample was repeatedly scanned between 200?00 nm, using Varian, Cary, 1E UV/visible spectrophotometer (Switzerland). However Tm-melted DNA was obtained by heating the mixtures at 100uC and snap cooled. After a brief incubation, scanning was taken between 200?00 nm. The above setup was also studied in the presence of varying concentration of Mg2+ (1?0 mM). The spectra of free drugs, free DNA or Tm-melted free DNA were obtained and treated as controls.Methylxanthines Binding with DNABinding constantsThe binding efficacy/activity of these three xanthines with DNA was ascertained at varying drug concentrations in P/D ratios (P/D 0.8, 1.0, 3.0 and 6.0), where the binding constants were obtained as reported [37,38]. In order to calculate the binding constant (K) for the DNA ?methylxanthines (theophylline or theobromine or caffeine) complex, it is alleged that DNAmethylxanthines complex forms in a ratio of 1:1, based on this the following equations can be established. DNAzMethylxanthines