GDP-sensitive permeabilities

Whereas the methods mentioned above all determine thermogenin amounts, the functional activity of thermogenin can be measured — at least in relative terms — by measuring GDP-sensitive Cl permeability [38,48]. 

Similarly, GDP-sensitive respiration (which is a measure of thermogenin-associ-ated (OH ) permeability) is an estimate of functionally active thermogenin — provided that a sufficiently efficient substrate is used (palmitoyl-camitine) such that respiration is thermogenin-limited (i.e., that an artificial uncoupler can stimulate respiration above the initial level). 

When changes in thermogenin concentration due to cold acclimation of hamsters were measured by GDP-binding, ELISA, GDP-sensitive swelling, and GDP-sensitive respiration, it was found that these parameters increased in parallel, indicating that all thermogenin was functionally active [38,57]. 

---