 ITPKB protein regulates inositol phosphate metabolism by phosphorylation of second messenger inositol 1,4,5-trisphosphate, which releases calcium from intracellular store in the endoplasmic reticulum by gating the inositol trisphosphate receptor.ITPKB produces Ins(1,3,4,5)P4, which does "not" gate the inositol trisphosphate receptor.The enzyme specifically phosphorylates the 1,4,5 isomer of IP3.