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 superstition respecting power and office is going to the ground. The stream of human affairs flows its own way, and is very little affected by the activity of legislators. What great masses of men wish done, will be done; and they do not wish it for a freak, but because it is their state and natural end.”
—Ralph Waldo Emerson (1803–1882)