INVOLVEMENT OF NITROREDUCTASE AND O-ACETYLTRANSFERASE ON THE MUTAGENICITY OF PLANT-ACTIVATED BENZIDINE AND 4-AMINOBIPHENYL

Benzidine and 4-aminobiphenyl (4-ABP) are activated by intact plant ce lls and cell free TX1MX into mutagenic metabolites that induce framesh ift and base pair substitution mutations in Salmonella typhimurium. Th e plant activation of these agents is plant peroxidase-mediated and ba cterial O-ocetyltransferase (OAT) dependent. TX1MX-activated benzidine and 4-ABP were analyzed with S. typhimurium frameshift tester strains , YG1021, YG1024, TA98, TA98NR, TA98/1,8-DNP6, MP219, and base pair su bstitution tester strains, YG1026, YG1029, TA100, TA100NR, TA100TN:OAT , and MP208. Concentration ranges for benzidine and 4-ABP were 1-50 mu M and 0.1-1 mM, respectively. This study was conducted to determine i f the plant-activation of benzidine and 4-ABP follows the prostaglandi n H synthase-mediated activation pathway in mammals [Smith et al. (199 2): Chem Res Toxicol 5;431-439]. In this model, benzidine is N-acetyla ted by S. typhimurium OAT. This acetylated product is a substrate for PHS and is converted into a 4-nitro product which is catalyzed by nitr oreductase into a N-hydroxy intermediate. The pathway assigns a specif ic role for nitroreductase in the activation of benzidine. By employin g S. typhimurium strains that express different levels of OAT and/or n itroreductase, we determined that the plant-activation of benzidine an d 4-ABP has an absolute requirement of bacterial OAT activity for the induction of frameshift mutations at hisD3052 and is required for the optimal mutagenic response at hisG46. Nitroreductase also plays a role in the plant activation of these agents. The data suggest that the pl ant-activation of benzidine and 4-ABP generates at least two classes o f proximal mutagenic intermediates. One class requires S. typhimurium OAT alone to be transformed into the ultimate mutagen and a second cla ss requires both OAT and nitroreductase. (C) 1997 Wiley-Liss, Inc.