Studies on the deiodination of 3,3',5'-T3 (reverse T3) to 3,3'-T2 (diiodothyronine) in rat liver.

Properties of the deiodination reaction of rT3 to 3,3' T2 in rat liver homogenate are reported and compared with T4 to T3 conversion under similar conditions. pH optimum and SH-group dependency of these two reactions are quite different, though both are concerned with 5' deiodination. The most potent activator of the reaction rT3 to T2' is dithiothreitol; the enzyme activity increases almost linearly even at very high concentration of this compound (the same is true for mercaptoethanol). Glutathione and coenzyme A, show only small activating effects. T4 to T3 and rT3 to T2' converting is being induced almost parallel in thyrectomized rats substituted with T4 or T3.