Radiometric enzyme assay for the type 2 iodothyronine deiodinase, based on the enzymic conversion of radioactive substrate to labeled products, and the measurement of radioactivity of products and residual substrate after their quantitative separation.
A:
An electronic image (made with the aid of laser scanner BAS-5000, see next figure) of optimized thin layer chromatographic separation of enormously small amount – femtomols (i.e., 10-15 (!) mol) of radioactive products ([125I]-3,5,3‘-triiodothyronine, T3 and [125I]-iodide) from unconsumed radio-labeled substrate ([125I]-thyroxine, T4) in the quantified enzymic reaction.
B:
The influence of subchronic administration to the rats (for 21 days) of antidepressant drug fluoxetine (Fluox), triiodothyronine (T3) and their combination, on the specific enzyme activity of deiodinase of type 2 (D2) in the rat pituitary. (As expected, fluoxetine caused a slight increase, and T3 very marked decrease, in pituitary D2 activity – due to feedback regulation of the extent of thyroid hormone metabolism by free T3).