Nicolas J P, Guéant J L
Unité INSERM 308, Faculté de Médecine, Vandoeuvre-les-Nancy.
Bull Acad Natl Med. 1994 Mar;178(3):551-65; discussion 565-8.
In our first communication, the complexity of vitamin B12 digestive transport was considered. This second presentation demonstrates the route of the vitamin in the body. As cobalamin or vitamin B12 has existed for Four Billion Years, they figure without any doubt amongst those molecules which have the most complex structure. The rarity of an architecture organised around a cobalt atom confirms their high level of originality. Their exceptional character is reflected in their cycle such as for mammals and for man where the intervention of binders, such as intrinsic factor, transcobalamin and haptocorrin is necessary for transporting them. As far as cellular metabolism is concerned, it is especially loaded sometimes with folates in the transfer of the methyl group. The Molecules are spiked with hydrophobic sites. Their membrane transfer is facilitated by several types of receptors. The intestinal absorption, which appears to require the presence of two receptors and two transporters, remains for the moment a unique assimilation model. The very probable existence of an enterohepatic cycle as well as a renal reabsorption saves this molecule, itself synthesised by microorganisms only.
在我们的首次交流中，探讨了维生素B12消化运输的复杂性。本次报告展示了维生素在体内的运输途径。由于钴胺素或维生素B12已存在40亿年，它们无疑是结构最为复杂的分子之一。围绕钴原子构建的罕见结构证实了它们高度的独特性。它们的特殊性质体现在其循环过程中，比如在哺乳动物和人类中，需要诸如内因子、转钴胺素和运钴胺蛋白等结合蛋白的参与来运输它们。就细胞代谢而言，在甲基转移过程中它有时会与叶酸结合。这些分子带有疏水位点。几种类型的受体促进了它们的膜转运。肠道吸收似乎需要两种受体和两种转运蛋白的存在，目前仍是一种独特的同化模式。极有可能存在的肠肝循环以及肾脏重吸收挽救了这种仅由微生物合成的分子。
