Phospholipids phosphomonoesterase

Fig. 1. The major inositol lipids. Phosphatidylinositol (Ptdlns), the major membrane inositol phospholipid, is phosphorylated to phosphatidylinositol 4-phosphate (Ptdlns 4-P) by a phosphatidylinositol kinase (a). Ptdlns 4-P is further phosphorylated to phosphatidylinositol 4,5-bisphosphate (Ptdlns 4,5-P2) by a phosphatidylinositol 4-phosphate kinase (b). Ptdlns 4,5-P, is converted back to Ptdlns 4-P by phosphatidylinositol 4,5-bisphosphate phosphomonoesterase (c) and then to Ptdlns by phosphatidylinositol 4-phosphate monoesterase (d). The pathway of phosphorylation and dephosphorylation constitutes a futile cycle and is only interrupted by agonist-induced hydrolysis of Ptdlns 4,5-P,.

PIP2 is formed in the cell membrane by the successive phosphorylation of the membrane phospholipid phosphatidylinositol (PI) to phosphatidylinositol 4-monophosphate (PIP) and then to PIP2. PIP2 is readily recycled by specific phosphomonoesterases to PIP and eventually back to PI. This cycle continues at rest until stimulation of surface receptors occurs. Receptor... 

Utilization of phosphate monoesters by microalgae and bacteria is effected by phosphomonoesterases (phosphatases) of broad specificity present at the cell surface. Hydrolytic release of PO4- from sugar phosphates, nucleotide phosphates, phospholipids, and phenyl phosphates, to name a few, enables a wide variety of phosphorus containing compounds to be utilized as phosphorus sources for growth of microbes. Ultrastructural observations and results from biochemical experiments indicate that extracellular phosphatases cleave the phosphate moiety from dissolved organic phosphorus compounds, which is then internalized, leaving the carbon skeleton outside the cell (Kuenzler and Perras, 1965 Doonan and Jensen, 1977). 

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