Effects of Histidine on Light-Induced DNA Single-Strand Cleavage by Selected Polycyclic Aromatic Hydrocarbons

The combination of UVA light and 1-aminopyrene, 1-hydroxypyrene, 1-hydroxybenzo[ a ]pyrene, 3-aminofluoranthene, 6-aminochrysene, or 5-, 6-, and 7-methylbenz[ a ]anthracenes causes DNA single-strand cleavage. 1-Hydroxypyrene, 1-hydroxybenzo[ a ]pyrene, and 5-methylbenz[ a ]anthracene have been shown to cause DNA cleavage, at least partially, by generating singlet oxygen. Therefore, the presence of histidine, a singlet oxygen quencher, should inhibit the DNA photocleavage. However, the presence of 50 mM histidine greatly enhances the DNA photocleavage caused by these compounds. This effect is due to the inhibition of the photodegradation of the PAH compounds. Therefore, care must be taken when interpreting the singlet oxygen quenching data by histidine. Histidine may coexist with PAHs that have entered the body. The presence of histidine can alter the photochemical reaction and, possibly, the phototoxicity mechanism of the PAHs.