Inositol-trisphosphate 3-kinase B is an enzyme that in humans is encoded by the ITPKB gene.
The protein encoded by the ITPKB gene is one of 3 isoforms of Inositol-trisphosphate 3-kinase expressed in humans. 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)P<small>4</small>, which does not gate the inositol trisphosphate receptor. The enzyme specifically phosphorylates the 1,4,5 isomer of IP<small>3</small>. The activity of this encoded protein is responsible for regulating the levels of a large number of inositol polyphosphates that are important in cellular signaling. Both calcium/calmodulin and protein phosphorylation mechanisms control its activity. Itpkb regulates immune cell function and is required for T and B cell development.