title: Studies on mechanism of 8-methoxypsoralen-DNA interaction in the dark.
abstract: The interaction of 8-methoxypsoralen (8-MOP) with calf thymus DNA was studied in darkness at 25 degrees C 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 1 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.
authors.affiliation: Institute of Biochemistry and Biophysics, University of Tehran, P.O. Box 13145-1384, Tehran, Iran.
authors.forename: A
authors.initials: A
authors.lastname: Arabzadeh
authors.forename: S Z
authors.initials: SZ
authors.lastname: Bathaie
authors.forename: H
authors.initials: H
authors.lastname: Farsam
authors.forename: M
authors.initials: M
authors.lastname: Amanlou
authors.forename: A A
authors.initials: AA
authors.lastname: Saboury
authors.forename: A
authors.initials: A
authors.lastname: Shockravi
authors.forename: A A
authors.initials: AA
authors.lastname: Moosavi-Movahedi
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002151:Calorimetry / Q000379:methods; D002417:Cattle; D004247:DNA / Q000378:metabolism*; D003624:Darkness; D004305:Dose-Response Relationship, Drug; D008730:Methoxsalen / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D004247:DNA; D008730:Methoxsalen