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Choline Kinase (also known as CK,ChoK and Choline Phosphokinase) is an enzyme which catalyzes the first reaction in the choline pathway for phosphatidylcholine (PC) biosynthesis.This reaction involves the transfer of a phosphate group from ATP to choline in order to form phosphocholine. :ATP + choline ADP + O-phosphocholine Thus, the two substrates of this enzyme are ATP and choline, whereas its two products are ADP and O-phosphocholine.Choline Kinase requires magnesium ions (+2) as a cofactor for this reaction. This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with an alcohol group as acceptor. The first detailed investigation of the enzyme was conducted by McCamen in 1962, where it was shown that the brain is the richest source of the enzyme in mammalian tissue. A related enzyme, ethanolamine kinase tends to co-purify with choline kinase leading to a suggestion that the two activities are mediated by two distinct active sites on a single protein. The systematic name of this enzyme class is ATP:choline phosphotransferase. These enzymes participate in glycine, serine and threonine metabolism and glycerophospholipid metabolism. In mammalian cells, the enzyme exists as three isoforms,CKα-1,CKα-2 and CKβ. These isoforms are encoded by two separate genes, CHKA and CHKB and are only active in their homodimeric,heterodimeric and oligomeric forms. == Structural studies == As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes , , , , , and . CKα-2 originating from C. elegans, is a dimeric enzyme with each monomer being composed of two domains.The active site is located between the two domains. (See figure below) Its overall structure is similar to members of the eukaryotic protein kinase family. Mammalian choline kinases exists in either dimeric or tetrameric forms in solution. Structural studies carried out on CKα-2, have implied that the conserved residues in the CK family of enzymes could possible play a vital role in substrate binding as well as in the stabilization of catalytically important residues.〔 An enlarged view of the residues involved in the dimer interface between the S-shaped loop of the yellow subunit and the loop following helix A and strand 4 of the cyan subunit. Only residues that are involved in direct salt bridges, hydrogen bonds, or van der Waals interactions are shown. Salt bridges and hydrogen bonds, dashed lines; labels of residues from the yellow subunit, red; labels of residues from the cyan subunit, blue. 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「Choline kinase」の詳細全文を読む スポンサード リンク
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