Enhancement of S9 activation by S105 cytosolic fraction.

The addition of supplementary cytosolic fraction greatly enhances the activation of 2-acetylaminofluorene (AAF) by uninduced 9,000 x g supernatant fractions (S9) in the Ames test. Uninduced S9 is poor at activating AAF in the Ames test (although it is effective in the liquid based fluctuation test) probably because cytosolic material diffuses into the bottom agar. An enhancing effect of cytosol supplementation was also observed with 2-aminoanthracene (AA) and 2-aminofluorene (AF) with uninduced S9. Using Aroclor-induced preparations, supplementation with cytosol enhanced the activation of benzo[a]pyrene and ethidium bromide. With AAF and Aroclor-induced preparations, supplementation with cytosol produces a slight but significant increase in activation, but interpretation is complicated by the fact that Aroclor 105,000 x g supernatant fraction (S105) alone efficiently activates AAF, AF and AA. Norharman potentiated the enhancing effect of Aroclor S105 on Aroclor-S9 activation of AAF but inhibited the activation of AAF by S105 fraction alone. The enhancing effect of S105 fraction may explain some, but not all, of the differences between liquid-based and agar overlay based activation.