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°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 hydroxyiase, 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 in vitro genotoxicity assays for at least 1 year.