UV irradiation is the most frequent cause of DNA abnormality produced by reactive oxygen species (ROS). Photochemistry of aromatic amino acids has widely been studied with regard to generation of ROS such as singlet oxygen (1O2) and superoxide (O2•–). In general, there are two main processes responsible for photosensitized reactions (scheme 1): (1) the chromophore is excited by light to a triplet state, and undergoes a direct electron or hydrogen exchange with a substrate, creating a free radical (Type I process); (2) energy transfer from the excited chromophore directly to oxygen, resulting in generation of 1O2 (Type II process). However, DNA damage by ROS generated by photoirradiation of aromatic amino acid or neurotransmitter with oxygen has yet to be reported. We report the effects of ROS produced by UV-B photoirradiation of a neurotransmitter, serotonin (5-hydroxytryptamine: 5-HT) and aromatic amino acids, tryptophan (Trp) and tyrosine (Tyr), with oxygen on DNA cleavage. UV-B photoirradiation of a neurotransmitter (5-HT) and aromatic amino acids (tryptophan and tyrosine) with oxygen results in DNA cleavage by generation of superoxide as demonstrated by agarose gel electrophoresis with pBR322 DNA. The reactive species for DNA cleavage is superoxide which was detected by ESR. The formation of O2•– upon photoexcitation of 5-HT with O2 by use of a mercury lamp is confirmed by the ESR spectrum measured at 77 K, where the anisotropic signals at g| = 2.080 and g^ = 2.002 are well assigned to O2•–. We also investigated electron-transfer dynamics of the formation of superoxide anion in electron transfer from the triplet excited state of neurotransmitter or aromatic amino acid to O2 by laser flash photolysis.The 2010 International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2010
