Activity of the inner and outer membrane oxidative enzymes in brown adipose tissue mitochondria.

1. The specific activity of cytochrome-oxidase, succinate-cytochrome c reductase and su-cinate-oxidase of brown adipose tissue mitochondria of 17-day-old rats was found to be twice as high in brwon adipose tissue mitochondria as in the liver. The specific activity of rotenone-sensitive NADH-cytochrome c reductase and NADH-oxidase was found to be six times higher in brown adipose tissue mitochondria than in the liver. 2. Brown adipose tissue mitochondria have extremely low activity of outer membrane enzymes. When compared with liver the specific activity of rotenone-insensitive NADH-cytochrome c reductase was found to be seven times lower, the specific activity of monoamineoxidase up to 30 times lower according to the substrate used. 3. The optimum conditions for the determination of both NADH-cytochrome c reductases in brown adipose tissue mitochondria were more specified on the base of the following findings: (a) the outer membrane rotenone-insensitive NADH-cytochrome c reductase is strongly inactivated by freezing-thawing, (b) freezing-thawing, alone is insufficient to release completely maximal activity of rotenone-sensitive NADH-cytochrone c reductase, freezing-thawing activite can be further potentiated by e.g. trypsin treatment. 4. The activities of the outer membranes of brown-adipose tissue mitochondria are discussed with regards to the structural integrity of the outer membrane, the activities of the inner membrane enzymes are discussed with regards to the functional specifity of the tissue.