Mitochondrial oxidative enzymes and phosphorylations in cold exposure and hibernation

Oxidative enzyme activities and oxidative phosphorylations of the liver mitochondria of a hibernating species, the golden hamster, and a nonhibernating species, the albino Wistar rat, were examined for changes in response to prolonged cold exposure. Succinic and glutamic oxidase, succinic-triphenyltetrazolium reductase, and cytochrome oxidase activities were measured. The mitochondria from cold-exposed rats showed no major changes (except for a high succinic-triphenyltetrazolium reductase activity), and normal P:O ratios (moles of phosphate esterified per gram atom O2 consumed). In both active and hibernating cold-exposed hamsters, all oxidative enzymes measured at 37 C were increased in activity, and the P:O ratios were normal. The mitochondria of hibernators contain a temperature-sensitive succinic oxidase system; when measured at 7 C, this activity is lower in the hibernators than in active cold-exposed animals or control animals. On the basis of the criteria used here hibernation does not involve a loss of oxidative capacity.