We have synthesized the first amino-substituted inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] analogue, D-3-amino-3-deoxy-myo-Ins(1,4,5)P3 (9). Although 9 is a full agonist at the Ca2+ mobilizing Ins(1,4,5)P3 receptor at pH 7.2 and 7.6, it is apparently a high intrinsic activity partial agonist at pH 6.8, releasing only 80% of the Ins(1,4,5)P3-sensitive Ca2+ stores of SH-SY5Y cells. Additionally, 9 was able to fully displace [3H]Ins(1,4,5)P3 from binding sites in rat cerebellum membranes at both pH 6.8 and 7.6, indicating a full interaction with the Ins(1,4,5)P3 receptor. The activity displayed by this amino analogue is unexpected and may be indicative of a pH-dependent conformational change in the amino acid residues comprising the Ins(1,4,5)P3 binding site.