Inositol 1,4,5-trisphosphate (IP3) is a second messenger for many growth factors, hormones, and neurotransmitters and, upon binding to the IP3 receptor (IP3R), triggers the release of intracellular, luminal calcium to the cytosol. Several additional cellular forms of inositol phosphates have been discovered. These include some which have been recently discovered and characterized to possess up to seven or eight phosphate groups, including pyrophosphates (PP-IPs: pyrophosphate-inositol phosphates). It has been proposed that high-energy pyrophosphates may participate in protein phosphorylation. Inositol-hexakisphosphate (IP6) kinase, or PiUS (Pi Uptake Stimulator) has ATP synthase activity and transfers a phosphate from PP-IP5 to ADP to form ATP thus suggesting an important physiological role for PP-IP5 and IP6 kinase.
ATP:1D-myo-inositol-hexakisphosphate phosphotransferase; IHPK2; Inositol hexakisphosphate kinase 2; inositol hexaphosphate kinase 2; InsP6 kinase 2; P(i)-uptake stimulator; pi uptake stimulator; PiUS