Russell-Jones G J, Alpers D H
C/- Biotech Australia Pty Ltd, Roseville, NSW, Australia.
Pharm Biotechnol. 1999;12:493-520. doi: 10.1007/0-306-46812-3_17.
The uptake of vitamin B12 from the intestine into the circulation is perhaps the most complex uptake mechanism of all the vitamins, involving no less than five separate VB12-binding molecules, receptors and transporters. Each molecule involved in uptake has a separate affinity and specificity for VB12 as well as a separate cell receptor. Thus VB12 is initially bound by haptocorrin in the stomach, then by IF in the small intestine. An IF receptor is then involved in uptake of the IF-VB12 complex by the intestinal epithelial cell, with the subsequent proteolytic release of VB12 and subsequent binding to TcII. The TcII receptor then transports the TcII-VB12 complex across the cell, whence it is released into the circulation. It is surprising, then, that despite its complexity, it has been possible to harness the vitamin VB12 uptake mechanism to enhance the oral uptake of peptides, proteins, and nanoparticles.
维生素B12从肠道吸收进入血液循环的过程，可能是所有维生素吸收机制中最为复杂的，涉及不少于五种独立的维生素B12结合分子、受体和转运蛋白。参与吸收的每个分子对维生素B12都有各自不同的亲和力和特异性，并且有各自独立的细胞受体。因此，维生素B12最初在胃中与钴胺素结合蛋白结合，然后在小肠中与内因子结合。接着，一种内因子受体参与肠道上皮细胞对内因子 - 维生素B12复合物的吸收，随后维生素B12通过蛋白水解作用释放出来，并随后与转钴胺素II结合。转钴胺素II受体随后将转钴胺素II - 维生素B12复合物转运穿过细胞，然后释放到血液循环中。那么，令人惊讶的是，尽管其过程复杂，但利用维生素B12的吸收机制来增强肽、蛋白质和纳米颗粒的口服吸收已成为可能。
