Quantifying Enzyme Activity
In vitro, including cell culture experiments, deiodination activity is determined by incubating cells or homogenates with high amounts of labeled thyroxine (T4) and required cosubstrates. As a measure of deiodination, the production of radioactive iodine and other physiological metabolites, in particular T3 or reverse T3, are determined and expressed e.g. as fmol/mg protein/minute.
In vivo, deiodination activity is estimated from equilibrium levels of free T3 and free T4. A simple approximation is T3/T4 ratio, a more elaborate approach is calculating sum activity of peripheral deiodinases (GD) from free T4, free T3 and parameters for protein binding, dissociation and hormone kinetics.
Read more about this topic: Iodothyronine Deiodinase
Famous quotes containing the word activity:
“Dissent is the native activity of the scientist, and it has got him into a good deal of trouble in the last years. But if that is cut off, what is left will not be a scientist. And I doubt whether it will be a man.”
—Jacob Bronowski (1908–1974)