Inositol-1,3,4-Triphosphate-5/6-Kinase (ITPK1)

This cDNA encodes a 414-amino acid polypeptide. ITRPK1 was expressed as a 3.6-kb message in all tissues tested, with the highest levels in brain. Expression of the cDNA resulted in inositol 1,3,4-trisphosphate 5/6-kinase activity, showing that a single kinase phosphorylates inositol in both the D5 and D6 positions.

Functional analysis showed that the variant, which they called the type beta protein, as well as the protein with asn356, which they called the type alpha protein, phosphorylated not only the 5- and 6-hydroxy groups of Ins(1,3,4)P3 but also the 1-hydroxy group of Ins(3,4,5,6)P4, suggesting that the 2 inositol phosphates compete for phosphorylation in vivo.