– Type I inositol 1,4,5-trisphosphate 5-phosphatase is a 412 amino acids protein that belongs to the inositol 1,4,5-trisphosphate 5-phosphatase type I family. Type I inositol-1,4,5-trisphosphate 5-phosphatase is an enzyme that in humans is encoded by the INPP5A gene. It is expressed in brain and high level in Purkinje cells. InsP3 5-phosphatases hydrolyze Ins(1,4,5)P3, which mobilizes intracellular calcium and acts as a second messenger mediating cell responses to various stimulation.