Changes in the liver mitochondrial oxidation of succinate during cold-exposure.

1. Exposure of rats to low environmental temperature resulted in increased activities of several hepatic oxidative-enzyme systems. 2. Simultaneous with increase in liver ubiquinone in cold-exposed rats, the ubiquinone-dependent succinate-neotetrazolium chloride reductase activity also increased. Such an increase could also be obtained by enriching liver with ubiquinone by feeding with an exogenous source. 3. Succinate-neotetrazolium chloride reductase activity could be increased by preincubation of mitochondria with succinate and the mechanism of this activation appears to be different from that obtained on addition of ubiquinone. 4. Succinate-neotetrazolium chloride reductase activity was found to be more labile than succinate dehydrogenase on freezing and thawing and storage, and the presence of succinate gave protection against this loss in hepatic mitochondria obtained from both normal and cold-exposed animals.