Module 2: Figure phosphoinositide metabolism
Summary of phosphoinositide metabolism.
The metabolism of phosphoinositides is separated into inositol lipid metabolism and inositol phosphate metabolism. In the former case, the parent molecule phosphatidylinositol (PtdIns) (Module 2: Figure PtdIns structure) undergoes a series of phosphorylation reactions to create various polyphosphoinositides many of which have messenger functions. For example, PtdIns4,5P2 functions both as a messenger and as a precursor for the formation of other phosphoinositide lipid signalling molecules such as PtdIns3,4,5P3. In addition, it can be hydrolysed to form the second messengers inositol 1,4,5-trisphosphate (Ins1,4,5P3) and diacylglycerol (DAG). The Ins1,4,5P3 is the major input into a complex pathway of inositol phosphate metabolism (Module 2: Figure inositol phosphate metabolism). One of the outputs of this metabolism is inositol that is used for the resynthesis of PtdIns. Cells also have a 1-L-myo-inositol-1-phosphate synthase that can convert glucose 6-phosphate (G-6-P) into inositol.