Photosensitized Cleavage of Plasmidic DNA by Norharmane, a Naturally Occurring â-carboline.

M. MICAELA GONZALEZ; MAGALI PELLON-MAISON; MATIAS A. ALES-GANDOLFO; MARIA R. GONZALEZ-BARÓ; ROSA ERRA-BALSELLS*; FRANCO M. CABRERIZO *

Organic and Biomolecular Chemistry

RSC

Año: 2010 vol. 8 p. 2543 - 2552

1477-0520

UV-A radiation (320-400 nm) induces damages to the DNA molecule and its components through photosensitized reactions. b-Carbolines (bCs), heterocyclic compounds widespread in biological systems, participate in several biological processes and are able to act as photosensitizers. The photosensitization of plasmidic DNA by norharmane in aqueous solution under UV-A radiation was studied. The effect of pH was evaluated and the participation of reactive oxygen species (ROS), such as hydroxyl radical (HO.), superoxide anion (O2-.) and singlet oxygen were investigated. A strong dependence of the photosensitized DNA relaxation on the pH was observed, being higher the extent of the reaction in the case of experiments performed at pH 4.7 than those performed at pH 10.2. As it was expected an intermediate extent of the reaction was observed at physiological pH (pH 7.4). Kinetic studies using ROS scavengers revealed that the chemical reactions between ROS and DNA are not the main pathways responsible for the damage of DNA. Consequently, the predominant mechanism yielding the DNA strand break takes place most probably via type I mechanism (electron transfer) from the single excited state (S1) of the protonated form of norharmane (1[nHoH+]*). Additional information about the nature of the norharmane electronic excited states involved in the photocleavage reaction was obtained by using the N-methyl derivative of norharmane (N-methyl-norharmane).