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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク intrinsic factor ： ウィキペディア英語版 intrinsic factor Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 (cobalamin) later on in the small intestine. In humans, the gastric intrinsic factor protein is encoded by the ''GIF'' gene. Haptocorrin (also known as HC, R protein, and transcobalamin I, TCN1), is a glycoprotein secreted by the salivary glands which binds to vitamin B12. Vitamin B12 is acid sensitive and in binding to transcobalamin I it can safely pass through the acidic stomach to the duodenum. Here in the less acidic environment of the small intestine, pancreatic enzymes digest the glycoprotein carrier and vitamin B12 can then bind to intrinsic factor. This new complex is then absorbed by the epithelial cells (enterocytes) of the ileum. Inside the cells, B12 dissociates once again and binds to another protein, transcobalamin II (TCN2). The new complex can then exit the epithelial cells to be carried to the liver. == Site of secretion == The intrinsic factor is secreted by the stomach. It is present in the gastric juice as well as in the gastric mucous membrane. The optimum pH for its action is 7 and it is inactivated at temperatures above 45 °C. It does not necessarily run parallel with the amount of HCl or pepsin in the gastric juice. So in some cases, the intrinsic factor may be present even if there is no HCl or pepsin or vice versa. The site of formation of the intrinsic factor varies in different species. In pigs it is obtained from the pylorus and beginning of the duodenum. In human beings it is present in the fundus and body of the stomach. The limited amount of normal human gastric intrinsic factor limits normal efficient absorption of B12 to about 2 mcg per meal, a nominally adequate intake of B12. 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「intrinsic factor」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.