Metabolic inactivation of 8-methoxypsoralen (8-MOP) by rat-liver microsomal preparations.

A modified Ames assay was developed that used an arginine-requiring mutant of Chlamydomonas reinhardii as an indicator organism. By counting the numbers of colonies formed and Arg+ revertants, we studied the influence of a rat-liver S9 mix (S9 fraction plus co-factors) on the toxic and mutagenic activities of 8-MOP plus black light. Both activities were decreased after pre-incubation of 5 micrograms 8-MOP/ml with S9 mix at 37 degrees C. S9 fractions without co-factors were almost completely inactive.