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:
“The teacher must derive not only the capacity, but the desire, to observe natural phenomena. In our system, she must become a passive, much more than an active, influence, and her passivity shall be composed of anxious scientific curiosity and of absolute respect for the phenomenon which she wishes to observe. The teacher must understand and feel her position of observer: the activity must lie in the phenomenon.”
—Maria Montessori (1870–1952)