Journal
INTERNATIONAL JOURNAL OF PHARMACEUTICS
Volume 237, Issue 1-2, Pages 47-55Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0378-5173(02)00020-0
Keywords
DNA; 8-MOP; intercalation; microcalorimetry; binding sites
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The interaction of 8-methoxypsoralen (8-MOP) with calf thymus DNA was studied in darkness at 25 degreesC and pH 7.4. The enthalpy curve for 8-MOP-DNA interaction was obtained by isothermal titration calorimetry and showed a two-step process for the interaction. According to the spectrophotometric data, it was suggested that some compaction may occur in the DNA structure at higher [8-MOP](t)/[DNA] ratio. Using the fluorescence quenching data, the Scatchard analysis was performed for 8-MOP-DNA interaction at the extended ranges of drug concentration. The results indicated that the first set of binding sites was occupied by I mol of drug bound per near eight base pairs of DNA. Also 8-MOP caused the quenching of the fluorescence emission of DNA-ethidium bromide complex. The Scatchard analysis of these data indicated the non-competitive manner for quenching. A non-displacement based quenching mechanism has been suggested for this behavior. The circular dichroism spectra also confirmed the non-intercalative binding of 8-MOP at higher concentrations accompanied by some conformational changes in DNA structure. It has been suggested that at low drug load, 8-MOP binds to DNA as an intercalator, which is an endothermic process. whereas at higher ratios of [8-MOP](t)/[DNA]. it binds to the outside of DNA, probably in the minor groove and causes some compaction in DNA, which is the exothermic process. (C) 2002 Elsevier Science B.V. All rights reserved.
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