| Health / Medical Topics |
Phosphoinositide Pathway
Nine currently identified phosphoinositide 3-kinases (PI 3-K) constitute a subfamily of lipid kinases that catalyze the addition of a phosphate molecule on the 3-position of the inositol ring of phosphoinositides. Phosphatidylinositol (PtdIns), the precursor of all phosphoinositides (PI), constitutes less than 10% of the total lipid in eukaryotic cell membranes. Approximately 5% of cellular PI is phosphorylated at the 4-position (PtdIns-4-P), and another 5% is phosphorylated at both the 4- and 5-positions (PtdIns-4, 5-P2). However, less than 0.25% of the total inositol-containing lipids are phosphorylated at the 3-position, consistent with the idea that these lipids exert specific regulatory functions inside the cell, as opposed to a structural function. Here we have chosen to highlight a group of the phosphoinositide targets of the PI3-Ks and their downstream targets. The downstream effects of these PI-3 targets are indicated, illustrating the important role the PI3Ks have in cell function and survival. (NCI Thesaurus/BIOCARTA)
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