ITPK1 (Inositol Tetrakisphosphate 1-Kinase)
Historical Background: Evolution of the Concept that ITPK1 Is a Cell-Signaling Enzyme
A 6-kinase activity that phosphorylates Ins(1,3,4)P3 to Ins(1,3,4,6)P4 (EC 220.127.116.11) was originally described in 1987 by two separate groups working independently (Balla et al. 1987; Shears et al. 1987). The gene encoding the 46 kDa 6-kinase was cloned almost 10 years later (Wilson and Majerus 1996). The enzyme also has a less active 5-kinase activity towards Ins(1,3,4)P3 (Shears 1989; Wilson and Majerus 1996), and so was generally referred to as an “inositol 1,3,4-trisphosphate 5/6-kinase.” This prompted the HGNC (the HUGO Gene Nomenclature Committee; http://www.genenames.org/) to accept that the corresponding gene could be named as ITPK1. Subsequently, the enzyme was found to also add a 1-phosphate to Ins(3,4,5,6)P4 (Yang and Shears 2000). This was a particularly significant observation from a cell signaling perspective, as Ins(3,4,5,6)P4 had...