Inositol-1,4,5-Trisphosphate-3-Kinase B (ITPKB)

ITPKB regulates inositol phosphate metabolism by phosphorylation of second messenger inositol 1,4,5-trisphosphate to Ins(1,3,4,5)P4. 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.Sequencing yielded an open reading frame encoding a 472-amino acid protein with a calculated relative mass of 53,451. The C-terminal part of ITPKB, namely residues 187 to 462, was 68% identical to ITPKA in amino acid sequence.Mitogenic stimulation of thymocytes resulted in decreased Ins(1,3,4,5)P4, but not Ins(3,4,5)P3, production.