The objective of this project was to investigate the equilibrium thermodynamic stability of the Iron-dependent repressor, IdeR, from Mycobacterium tuberculosis. As a function of bound metal, urea-induced isothermal equil ibrium denaturation experiments were used.. The goal was to measure the total free energy change upon metal bi nding, DGmetal_binding, of IdeR to complement ongoing experiments that directly measure ligand binding energet ics. To calculate DGmetal_binding, the free energy of unfolding of metal bound IdeR, holo-IdeR, and unbound Id eR, apo-IdeR, were measured by monitoring the changes in the intrinsic fluorescence of tryptophan residues. Th e difference of free energy of unfolding between holo and apo yields DGmetal_binding. The results are used to constrain models for IdeR’s activation.