[Comparison of photomutagenic activities of 5-mop (bergapten) and 8-mop (xanthotoxin) in chlamydomonas reinhardii (author's transl)].

The photomutagenic and phototoxic activities of 5-MOP and 8-MOP were compared in arg- cells of Chlamydomonas reinhardii and their ability to revert to Arg+ mutants. We determined the dependency of induction of Arg+ revertants from cell density, substance concentrations, UV-A fluence, and UV-A radiation intensities. Both furocoumarins were also tested for photomutagenicity under white-light conditions. In all experiments, 5-MOP was more active than 8-MOP. Only on the basis of saturation did both compounds show similarly strong mutagenic activities. When compared on the basis of equivalent cytotoxicity, the different between the activities of 5-MOP and 8-MOP was smaller. The difference between the activities of the 2 compounds was higher when white light was used instead of UV-A. We could not find any strong reciprocity between substance concentration and UV-A fluence or between UV-A fluence and radiation intensity. We believe that the difference between the photomutagenic activities of 5-MOP and 8-MOP in Chlamydomonas reinhardii is caused by their different abilities to form intercalation complexes with DNA which thus determine the kinetics of the following photochemical reactions. In addition, the results presented here suggest that the mutagenic and cancerogenic potency of 5-MOP is similar to or even stronger than that of 8-MOP. The cancerogenic risk of both compounds may be markedly diminished by reducing the UV-A radiation intensities during photochemotherapy.