The influence of thyroid hormones on normal rat-liver mitochondria I. Changes associated with the inhibition of phosphorylation by thyroxine added to untreated mitochondria

Abstract

1. 1. A study of the uncoupling of oxidative phosphorylation by thyroxine in the presence of MgCl 2 has demonstrated that the reduced phosphorylation efficiency was associated with an inhibition of the terminal phosphate-transferring reactions and a slowing of the rate of substrate oxidation. These initial effects were followed by a loosening of respiratory control. No pretreatment of the mitochondria was necessary in order to observe the effects although it was essential that the thyroxine be added to the incubation medium after the mitochondria. 2. 2. Thyroxine did not induce mitochondrial swelling under the conditions required for phosphorylation. However, contrary to the observations of other investigators, thyroxine did induce mitochondrial swelling in the presence of adenosine 5′-triphosphate and MgCl 2. At high levels of adenosine 5′-triphosphate the swelling was followed by an increase in the adenosine-5′-triphosphatase activity of the mitochondria.