So, what's a review on inositol phosphates doing in a nice lipid-themed place like this? (given how watersoluble and un-lipiddy they are). But they are, at least in animal cells, inextricably linked with inositol lipids. The link is the phospholipase C (PI-PLC) reaction, which splits phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] into diacylglycerol and Ins(1,4,5)P3, of which the latter mobilizes intracellular Ca2+ (this well-known inositol phosphate will not be discussed further). Over the last few years, a consensus has emerged that the PI-PLC reaction is also the starting point of all inositol phosphate synthesis in animal cells (Figure 1). Some organisms, especially InsP6-obsessives such as higher plants (who make lots of InsP6 to use as a phosphate-storage compound) and slime moulds (who make even more InsP6 even more quickly, for reasons known only to slime moulds) can also phosphorylate inositol sequentially up to InsP6 without any lipid intermediate. But we animals apparently have to start with Ins(1,4,5)P3 generated from PtdIns(4,5)P2 to make all our inositol phosphates.

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