Thyroxine and the Release of Protein fromRat Liver Mitochondria

Abstract

Thyroactive compounds at concentrations down to 5 × 10⁻⁶ M have the property of decreasing the amount of protein released by rat liver mitochondria in a suspending medium of either sucrose or phosphate at pH 7.4. This reaction is marked after 30 minutes at 37 C but is detectable at 25 C. A small amount of protein is released during the phase of rapid swelling produced by thyroid hormones, but thereafter the protein content of the suspending medium remains almost constant. By contrast, the delayed swelling noted in solvent controls is accompanied by continuous release of larger amounts of protein. Both magnesium ions and ATP at high concentrations affect the reaction in a complex manner, decreasing the release of protein in the solvent controls, an effect that is antagonized by the thyronines. These findings may be related to the preservation by thyronines of the failing metabolic systems of isolated tissues.