Development of peroxisomal beta-oxidation activities in brown fat of perinatal rabbits.

The development of peroxisomal activities in brown fat was analyzed in perinatal rabbits, 25- and 30-day fetuses, newborns, 5- and 10-day-old pups. Purified peroxisomal fractions were obtained from brown fat homogenates by sucrose gradient centrifugation at a density of 1.22 g/cm3. Enzymes specifically associated with the isolated peroxisomes, acyl-CoA oxidase, catalase and KCN-insensitive beta-oxidation, were most active in 25-day fetuses and much less active after birth. Mitochondrial-associated activities such as cytochrome c oxidase were greatest at birth. The beta-oxidation enzymes, enoyl-CoA hydratase, beta-hydroxyacyl-CoA dehydrogenase, and thiolase were present in mitochondrial as well as peroxisomal fractions. Nevertheless, the levels of these three enzymes in peroxisomes were higher in fetuses. Thus, peroxisomes, in contrast to mitochondria, were most active prior to birth. This suggests that peroxisomes do not participate in brown fat thermogenesis but that they have some role in priming the development of brown fat in perinatal rabbits.