The effect of thyroxine on ascorbic acid oxidation.

After numerous negative experiments on the possible effect of thyroxine on oxidations in animal tissue slices and homogenates, experiments were tried with this hormone on a vegetable enzyme, ascorbic acid oxidase. It was found that small amounts of thyroxine stimulated the oxygen uptake of the ascorbic acid-ascorbic acid oxidase system. Since ascorbic acid oxidase is a copper protein (I), the effect of thyroxine was studied on the cupric ion-induced oxidation of ascorbic acid. In this case, an inhibition of oxidation was obtained which was proportional to the thyroxine concentration.