Signaling with Phosphoinositides: Better than Binary

Phosphoinositide turnover. The reversible production of phosphoinositides (PIs) is catalyzed through the combined activities of a number of specific phosphatases and phosphoinositide kinases (i.e., x-Pases and PIxKs, respectively, where x designates substrate specificity with regard to the inositol ring). Cells utilize this PI network to support and distribute endocytic, exocytic, and signal transduction pathways that are, in turn, dependent upon a battery of proteins containing discrete, modular domains (viz., signaling domains) that bind to specific PIs. The figure also shows the turnover of PI4,5P₂ by phospholipase C (PLC) to yield soluble inositol-1,4,5P₃ and membrane-embedded diacylglycerol.