Effect of thyroxine on the latent apyrase activity of canary liver mitochondria.

Abstract

RECENT biochemical studies on the action of thyroid hormones have > indicated that such hormones as thyroxine and triiodothyronine uncouple the oxidative phosphorylation in mammalian liver mitochondria in vitro and in vivo (1, 2, 3, 4, 5). It is also well known that 2,4-dinitrophenol (DNP) is the strong uncoupling agent and it activates strikingly the latent apyrase2 activity of liver mitochondria (6, 7). Therefore it may be expected that thyroxine activates the enzyme action. In this respect, Lardy and Maley (5) have already observed an acceleration of ATP breakdown in aged rat liver mitochondria by a number of thyroid hormones in vitro. This present investigation was undertaken to observe the effect of thyroxine on the latent apyrase activity of fresh liver mitochondria. We used mouse serum in this experiment, because Klemperer (2) succeeded in demonstrating the in vitro uncoupling effect of thyroxine in normal rat liver mitochondria by introducing sheep serum into the reaction mixture.