Activation of 2-amino-6-methyldipyrido[1,2-a:3' ,2' -d]imidazole, a mutagenic pyrolysis product of glutamic acid, to bind to microsomal protein by NADPH-dependent and -independent enzyme systems.

The conversion of 2-amino-6-methyldipyrido[1,2-a:3' ,2' -d]-imidazole (Glu-P-1), a highly mutagenic principle in a pyrolysate of glutamic acid, to protein-bound metabolites in vitro was examined with microsomes from various tissues of female F344 rats. Addition of NADPH to the incubation mixture containing microsomes and [14C]Glu-P-1 increased the binding of its metabolites to microsomal proteins linearly with time for up to 30 min, while on addition of arachidonic acid the binding increased linearly only for the first 2-4 min of incubation and then levelled off. However, due to the initial rapid binding, addition of arachidonic acid resulted in 6-fold greater binding of metabolites to small intestinal microsomes than addition of NADPH on incubation for 4 min, and with microsomes from liver and colon, arachidonic acid was found to be a better cofactor than NADPH for activation of Glu-P-1. Indomethacin significantly inhibited the increase in binding by arachidonic acid. Additions of linoleic and linolenic acids also increased the binding, but addition of oleic acid had no influence. With hepatic microsomes from 3-methylcholanthrene-treated rats, binding within 4 min after addition of arachidonic acid was greater than that after addition of NADPH and the reverse on further incubation. These findings suggest that prostaglandin synthetase may serve as an alternative enzyme to cytochrome P-450 monooxygenases for conversion of Glu-P-1 to active intermediates in all the rat tissues investigated.