Phosphocholine phosphatase

L-Serine kinase, L-serine-3-phosphate decarboxylase 2 phosphoethanolamine phosphatase 3 ethanolamine kinase 4 phosphocholine phosphatase 5 choline kinase 6 ethanolamine phosphate cytidylyltransferase 7 ethanolamine phosphotransferase (D 3.2.4), phosphatidyl ethanolamine methyltransferase, phospholipase D, choline kinase 8 choline phosphate cytidylyltransferase... 

Fig. 6.12. Formation and function of the messenger substance ceramide. The starting point for the synthesis of ceramide is sphingomyelin, which is converted to phosphocholine and ceramide by the action of a sphingomyelinase. Sphingomyelinase is activated via a pathway starting from tumor necrosis factor a (TNFa) and its receptor. Ceramide serves as an activator of protein kinases and protein phosphatases. RI fatty add side chain.

Other compounds, not shown in Table VI, which are hydrolyzed by alkaline phosphatase are TPN (28), poly A (28), phosphocellulose (28), pyrophosphoserine (102, 103), phosphoserine (102-104), pyridoxine phosphate (104), pyridoxal phosphate (104), phosphothreonine (104), and phosphocholine (104) These compounds are all hydrolyzed at approximately the same rate. 

Barak and Tuma (1981) described the assay of choline by use of periodide. A colored complex is formed, and its absorbance is measured in 1,2-dichloroethane. The limit of detection is close to 0.5 p.g choline. If phosphocholine is present also, then it must be degraded by a phosphatase to yield free choline. 

FIGURE 6.1 Phosphatidylcholine (PC) synthesis by the CDP-choline pathway. First, choline is converted to phosphocholine then the CMP moiety of CTP is transferred to phosphocholine to form CDP-choline. Cleavage of the pyrophosphate (PPj) produced by phosphatases markedly reduces its concentration in the cell and ensures that the reaction is driven in the forward direction. The phosphocholine moiety of CDP-choline then is transferred to diacylglycerol, generating PC. The total number of phosphate-phosphate bonds (phosphodiester bonds) broken in this pathway is three. This number determines the energy cost of PC synthesis. All cells containing a nucleus can make PC via the CDP-choline pathway. 

CTP phosphocholine cytidylyltransferase (3) glycerol kinase (4) acyl-CoA glycerol-3-phosphate acyltransferase (5) acyl-CoA acyl glycerol-3-phosphate acyltransferase (6) phosphatidic acid phosphatase (7) CDP-choline diacylglycerol phosphocholine transferase. 

Fig. 1. Phospholipid biosynthetic pathways in animal cells. The abbreviations are DHAP, dihydroxyacetone phosphate G-3-P, glycerol-3-phosphate PA, phosphatidic acid DG, diacylglycerol CDP-DG, cytidine diphosphodiacylglycerol PI, phosphatidylinositol PG, phosphatidylglycerol PG-P, phosphatidylglycerol phosphate DPG, diphosphatidylglycerol PP, phosphatidic acid phosphatase PE, phosphatidylethanolamine PC phosphatidylcholine PEMT, phosphatidylethanolamine A-methyltransferase CT, CTP phosphocholine cytidylyltransferase PS, phosphatidylserine CK/EK, choline/ethanolamine kinase CPT, CDP-choline 1,...

In the first mechanism, phosphatidic acid is cleaved by a phosphatase to form diacylglycerol (DAG). DAG then reacts with an activated head group. In the synthesis of phosphatidylcholine, the head group choline is activated by combining with CTP to form CDP-choline (Fig. 33.28). Phosphocholine is then transferred to carbon 3 of DAG, and CMP is released. Phosphatidylethanolamine is produced by a similar reaction involving CDP-ethanolamine. 

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