Redox-dependent axial ligand replacement and its functional significance in heme-bound iron regulatory proteins

Both iron regulatory protein (IRP)-1 and 2 bind heme to the heme regulatory motif (HRM), but only IRP2 forms a 5-coordinate His-ligated heme immediately after the reduction. The formation of the 5-coordinate species probably due to the structural flexibility of IRP2 would differentiate function of heme in two IRPs.79