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The CDP-choline pathway, first identified by Eugene Kennedy in 1956, is the predominant mechanism by which mammalian cells synthesize phosphatidylcholine (PC) for incorporation into membranes or lipid-derived signalling molecules. The CDP-choline pathway represents one half of what is known as the Kennedy pathway. The other half is the CDP-ethanolamine pathway which is responsible for the biosynthesis of the phospholipid product phosphatidylethanolamine (PE).〔 The CDP-choline pathway begins with the uptake of exogenous choline into the cell. The first enzymatic reaction is catalyzed by choline kinase (CK) and involves the phosphorylation of choline to form phosphocholine. Phosphocholine is then activated by the addition of CTP catalyzed by the rate-limiting enzyme, CTP:phosphocholine cytidylyltransferase to form CDP-choline. The final step of the pathway involves the addition of the choline headgroup onto a diacylglycerol (DAG) backbone to form PC, catalyzed by choline/ethanolamine phosphotransferase (CEPT).〔 Phosphatidylcholine can be acted upon by phospholipases to form different metabolites. == Choline transport == Mammalian cells are unable to synthesize choline ''de novo'' and therefore must rely on exogenous sources from the diet. The uptake of choline is accomplished predominantly by the high-affinity, sodium dependent choline transporter (CHT) and requires ATP as an energy source. On the other hand, choline many enter the cell through the activation of low-affinity, sodium-independent organic cation transport proteins (OCTs) and/or carnitine/organic cation transporters (OCTNs), and do not require ATP. Lastly, choline may enter the cell through intermediate-affinity transporters, which include the choline transporter-like protein 1 (CTL1). The fate of internalized choline depends on the cell type. In pre-synaptic neurons the majority of choline will be acetylated by the enzyme choline acetyltransferase to form the neurotransmitter acetylcholine. Mst other cells will phosphorylate choline by the enzyme choline kinase, the first committed step of CDP-choline pathway. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CDP-choline pathway」の詳細全文を読む スポンサード リンク
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