Stability of Aroclor 1254-induced rat liver postmitochondrial supernatant (S-9) following long-term storage (-75 degrees C).

The stability of Aroclor 1254-induced rat liver postmitochondrial supernatant (S-9) over a 5-year period was investigated in a retrospective study. S-9 was uniformly prepared at 6-month intervals, and aliquots were stored at -75 degrees C. The protein and cytochrome P-450 content of these lots of S-9 were very similar, and no differences attributable to duration of storage were observed in the activities of ethoxycoumarin O-deethylase, aniline hydroxylase, cytochrome P-450 reductase or aryl hydrocarbon hydroxylase. There was no decrease following 5 years of storage in the ability of S-9 to activate 2-aminoanthracene, as measured in the Ames test (TA98), but there was a notable reduction following more than 1 year of storage in the ability of the S-9 to generate Ames test activity with benzo(a)pyrene. Based on the results of these studies, S-9 prepared and stored under these conditions appears to be suitable for use in vitro genotoxicity assays for at least 1 year.