Seetharam B, Jimenez M, Alpers D H
Am J Physiol. 1983 Jul;245(1):G72-7. doi: 10.1152/ajpgi.1983.245.1.G72.
Human bile or commercially available bile acids bind [57Co]cobalamin (Cbl) due to the presence of "R"-type binders, which are normally present in the former and present as a contaminant in the latter. The competition of these R proteins for the binding of Cbl by intrinsic factor (IF) could explain the in vivo inhibition attributed previously to the bile acids themselves. R protein seems to be involved in the inhibition of Cbl binding because protease digestion of either bile or bile acid abolishes the Cbl binding ability. Moreover, antibody to R protein abolishes the inhibition. Bile or bile acids do not have a direct effect on either purified IF or the IF-Cbl receptor molecule, even though bile acids increase the attachment of IF-[57Co]Cbl to ileal brush-border membranes. These data demonstrate two steps where components of bile could affect Cbl absorption: the binding of Cbl to IF and of IF-Cbl to its ileal receptor. It is not clear whether these in vitro phenomena are important for the normal absorption of Cbl in vivo.
由于存在“R”型结合蛋白，人胆汁或市售胆汁酸会结合[57Co]钴胺素（Cbl），“R”型结合蛋白通常存在于前者中，而在后者中则作为污染物存在。这些R蛋白与内因子（IF）竞争结合Cbl，这可以解释先前归因于胆汁酸本身的体内抑制作用。R蛋白似乎参与了Cbl结合的抑制，因为对胆汁或胆汁酸进行蛋白酶消化会消除Cbl的结合能力。此外，针对R蛋白的抗体也消除了这种抑制作用。胆汁或胆汁酸对纯化的IF或IF-Cbl受体分子没有直接影响，尽管胆汁酸会增加IF-[57Co]Cbl与回肠刷状缘膜的附着。这些数据表明胆汁成分可能影响Cbl吸收的两个步骤：Cbl与IF的结合以及IF-Cbl与其回肠受体的结合。目前尚不清楚这些体外现象对体内Cbl的正常吸收是否重要。
