CDP-Choline:diacylglycerol

Finally PC is made by releasing the CMP group in the process of fusing phosphocholine to diacylglycerol (DAG) by the enzyme CDP-choline 1,2-diacylglycerol choUnephosphotransferase (CPT McMaster and Bell, 1997). One cloned isoform of CPT seems specific for CDP-choUne, whereas another CPT also can synthesize PE from CDP-ethanolamine and DAG (Henneberry and McMaster, 1999 Heimeberry et al., 2000). 

McMaster, C.R., and BeU, R.M., 1997, CDP-choline 1,2-diacylglycerol cholinephospho-transferase. Biochim. Biophys. Acta 1318 100-110... 

Note that the enzymes CDP-choline 1,2-diacylglycerol transferase in phospholipid synthesis and acyl-CoA transferase in triglyceride synthesis have the common substrate 1,2-diacylglycerol thus we have this two-way synthesis shown in Fig. 13-13. 

Fig. 3. Regulation of PC biosynthesis via the CDP-choline pathway by modulation of the binding of CTP phosphocholine cytidylyltransferase (CT) to membranes. Three different modes of regulation of CT activity are indicated. The abbreviations are CK, choline kinase CPT, CDP-choline 1,2-diacylglycerol cholinephos-photransferase PEMT, phosphatidylethanolamine Af-methyltransferase PC, phosphatidylcholine PE, phos-phatidylethanolamine DG, diacylglycerol.

CMP + Phosphatidylcholine (catalyzed by CDP-Choline 1,2-Diacylglycerol Phosphocholine Transferase), , ... 

CDP-Choline 1,2-diacylglycerol phosphocholine transferase catalzyes the following reaction in the biosynthetic pathway leading to phosphatidylcholine (Figure 19.5)... 

McMaster, CR Bell, RM. CDP-choline 1,2-diacylglycerol choline phosphotransferase. 

This enzyme [EC 2.7.S.2] (also known as CDP-choline l,2-diacylglycerol cholinephosphotransferase, diacylglycerol cholinephosphotransferase, phosphoryl-choline glyceride transferase, alkylacylglycerol cholinephosphotransferase, and l-alkyl-2-acetylglycerol cholinephosphotransferase) catalyzes the reaction of CDP-choline with 1,2-diacylglycerol to produce CMP and a phosphatidylcholine. l-Alkyl-2-acylglycerol derivatives can also serve as substrates. 

A possible route for the reincorporation of phospholipid diacylglycerols is the pathway described by Kanoh and Ohno (1973) in which CDP-choline 1,2-. n-diacylglycerol transferase is reversed ... 

PC is synthesized in plant cells via the CDP-choline pathway, which includes three enzymatic steps catalyzed by choline kinase (EC 2.7.1.32 CKI), CTPiphosphocholine cytidylyltransferase (EC 2.7.7.15 CCT) and CDP-choline diacylglycerol choline-phosphotransferase (EC 2.7.8.2 CPT). Among them, CCT has been reported to be a rate-limiting enzyme [3]. 

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