Effect of thyroid hormone on carbohydrate content of Na+-K+-adenosine triphosphatase.

The effect of L-3,5,3'-triiodothyronine (T3) (50 micrograms/100 body wt) on the incorporation of labeled glucosamine and fucose into the subunits of Na+-K+-ATPase was examined by gel electrophoresis in sodium dodecyl sulfate. T3 augmented the incorporation of glucosamine into the alpha- and beta-subunits by 51 and 58%, respectively, in the 22-h chase experiments. Similarly T3 augmented the incorporation of fucose into the alpha- and beta-subunits by 58 and 43%, respectively. Reverse T3 did not alter the incorporation of labeled fucose in either subunit. The effect of T3 on the rate constant of degradation of renal cortical Na+-K+-ATPase was assessed. The rate constant of degradation (Kd) of the [3H]fucose labeled alpha- and beta-subunits for the hypothyroid rats were both 0.20, and for T3-treated rats, the Kd of the alpha- and beta-subunits were 0.23 and 0.18, respectively, suggesting that T3 enhanced fucose incorporation into the subunits of Na+-K+-ATPase rather than retarding the degradation of this enzyme.