Freezing affects the activity and subcellular distribution profile of human placental xenobiotic- and steroid-metabolizing enzymes.

Human placentae from both smoking and non-smoking mothers were examined with respect to the activity and apparent subcellular distribution of cytochrome P-450-linked xenobiotic-and steroid-metabolizing activities. Freezing of the placental sample in pieces before preparing mitochondria and microsomes led to decreases in some catalytic activities and changed the distribution profile of activities between mitochondria and microsomes. Cholesterol side-chain cleavage enzyme and aryl hydrocarbon hydroxylase were especially sensitive to the destructive effect of freezing. Activities in the microsomes were apparently more sensitive to freezing than were those in the mitochondrial fraction. In addition to the destruction of activities by freezing, cross-contamination of microsomes and mitochondria was postulated. Freezing tended to level off the differences between induced and uninduced material. In JEG cells, the specific activities of xenobiotic-metabolizing enzymes were higher in the mitochondrial fraction. In liver biopsy samples the expected, principally microsomal, localization of xenobiotic-metabolizing enzymes was observed. It is suggested that the placenta should be processed fresh at least as far as the postmitochondrial supernatant before freezing to avoid the destructive and cross-contaminating effects of freezing.