Activation of IDE by Ins(1,4,5)P3 and phytic acid [Ins(1,2,3,4,5,6)P6]. IDE activity was measured using the fluorogenic peptide Abz-GGFLRKHGQ-Eddnp at the indicated concentrations in 50 mM Tris buffer pH 7.4 with and without the addition of 50 µM Ins(1,4,5)P3 or 5 µM phytic acid.