Instability of mixed function monooxygenases in frozen rat liver

The effect of freezing in liquid nitrogen and storage at -74 degrees C on various parameters of rat livers from phenobarbital-induced and untreated animals was investigated. Marked instability of microsomal aminopyrine N-demethylase activity and cytochrome P-450 content were detected upon freezing and immediate thawing, leading to the conclusion that this may not be an acceptable means of storage of rat liver for studies of the mixed function oxidase enzymes.