DETECTION OF MUTAGENICITY IN AMES TEST USING A METALLOPORPHYRIN OXIDANT MODEL SYSTEM FOR CYTOCHROME-P450/

A chemical model system for cytochrome P450, a porphyrin and an oxidan t, was used in Ames assay as a substitute for S9 mix. in the presence of tetrakis(pentafluorophenyl)porphyrinatoiron(III) chloride [Fe(F5P)C l] and tert-butyl hydroperoxide (t-BuOOH), mutagenicity of N-nitrosodi butylamine (NDB) in Salmonella typhimurium TA1535 was detected. The mu tagenicity depended on the pre-incubation period, and also on the conc entration of an oxidant and of bacteria. In the chemical model system, pH affected the mutagenicity of NDB, which suggested that as observed in an enzymatic activating system, the mutagenicity was due to the la bile alkylating species which was derived from NDB activated in the ch emical activation system and was sensitive to pH. Under the optimum co nditions; a higher concentration of an oxidant, a higher concentration of bacterial culture, and a weakly acidic medium, mutagenicity of N-n itrosodipropylamine in S. typhimurium TA1535 was also detected. Beside s N-nitrosodialkylamines, 2-aminofluorene (2-AF) and benzo[a]pyrene (B aP) were also used as mutagens. Mutagenicity of 2-AF and BaP in S. typ himurium TA1538 were both detected in the same system as used in detec ting the mutagenicity of N-nitrosodialkylamines. Ames test using a met alloporphyrin/oxidant model system makes it possible to detect mutagen icity derived from both base pair substitution mutagens and frameshift mutagens without using enzymatic activating system. These results dem onstrate that the assay with the chemical model system is useful in de tecting unstable unknown active mutagens or investigating the mechanis ms of the metabolic pathway of mutagens or carcinogens in a protein-fr ee medium.