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Pathway Description
Choline Biosynthesis I
Arabidopsis thaliana
Metabolic Pathway
Choline is a nitrogen-containing, water-soluble nutrient that is incorporated into the headgroups of membrane phospholipids such as phosphatidylcholine. Two pathways exist for choline biosynthesis whereby serine becomes choline. Both of these pathways take place in the cytosol. This is the first pathway of choline biosynthesis. First, serine decarboxylase (SDC) uses a proton and a pyridoxal 5'-phosphate cofactor to catalyze the conversion of L-serine to ethanolamine, producing carbon dioxide as a byproduct. Second, ethanolamine kinase, localized to the cell membrane (coloured dark green in the image), uses ATP to catalyze the conversion of ethanolamine to O-phosphoethanolamine. Note that this is only the probable ethanolamine kinase in Arabidopsis thaliana and requires further research to confirm its function. Steps 3, 4, and 5 are catalyzed by phosphoethanolamine N-methyltransferase (PEAMT). These three sequential N-methylation steps convert phosphoethanolamine to phosphocholine and utilize S-adenosyl-L-methionine as a methyl donor. The intermediates are as follows: O-Phosphoethanolamine, N-methylethanolamine phosphate, and N-dimethylethanolamine phosphate. Sixth, phosphoethanolamine/phosphocholine phosphatase catalyzes the synthesis of choline from phosphocholine. It requires magnesium as a cofactor.
References
Choline Biosynthesis I References
BeGora MD, Macleod MJ, McCarry BE, Summers PS, Weretilnyk EA: Identification of phosphomethylethanolamine N-methyltransferase from Arabidopsis and its role in choline and phospholipid metabolism. J Biol Chem. 2010 Sep 17;285(38):29147-55. doi: 10.1074/jbc.M110.112151. Epub 2010 Jul 22.
Pubmed: 20650897
Lin YC, Liu YC, Nakamura Y: The Choline/Ethanolamine Kinase Family in Arabidopsis: Essential Role of CEK4 in Phospholipid Biosynthesis and Embryo Development. Plant Cell. 2015 May;27(5):1497-511. doi: 10.1105/tpc.15.00207. Epub 2015 May 12.
Pubmed: 25966764
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