A phosphatidic acid combined with inositol found in biomembranes and a precursor to certain cellular signals. Sometimes referred to as inositide. SYN: phosphoinositide.
- p. 4,5-bisphosphate (PIP2, PtdIns(4,5)P2) p. with two additional sites of phosphorylation; an important constituent of cell membrane phospholipids as well as a precursor of the second messengers, diacylglycerol and inositol 1,4,5-trisphosphate.
- p. 4-phosphate the intermediate in the biosynthesis of p. 4,5-bisphosphate from p..
- p. synthase an enzyme that catalyzes the reaction of CDP-diacylglycerol with inositol to form CMP and p.; found in the endoplasmic reticulum.
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phos·pha·ti·dyl·ino·si·tol (PI) (fos″fə-ti″dəl-ĭ-noґsĭ-tol) a phospholipid in which the sugar inositol is attached to the phosphate group of phosphatidic acid by an ester linkage and the fatty acyl groups are usually arachidonate and stearate; additional phosphates can be attached to the sugar. It is a minor constituent of cell membranes found primarily in the plasma membrane. It is converted by specific kinases to mono- and diphosphorylated forms, phosphoinositides involved in hormonally activated calcium mobilization.Medical dictionary. 2011.