Donaldson R M, Mackenzie I L, Trier J S
J Clin Invest. 1967 Jul;46(7):1215-28. doi: 10.1172/JCI105615.
Hamster intrinsic factor (IF) preparations markedly enhanced the uptake of (57)cobalt-labeled cyanocobalamin (B(12)-(57)Co) by brush borders and microvillous membranes isolated from villous absorptive cells obtained from the distal but not the proximal half of hamster intestine. A similar effect was observed with rat and rabbit IF preparations, but IF preparations obtained from man, dog, and hog were ineffective. After fractionation of hamster IF preparations by gel filtration or ion exchange chromatography, the extent to which each fraction enhanced B(12)-(57)Co uptake by brush borders correlated closely with the vitamin B(12) binding capacity of the fraction. IF-mediated attachment of B(12)-(57)Co to brush borders occurred rapidly, was not diminished by removal of glucose or oxygen from the incubation medium, and was not significantly altered when incubation temperatures were reduced from 37 degrees C to 7 degrees C. Marked reduction in uptake occurred, however, in the absence of divalent cations. IF enhanced B(12)-(57)Co uptake by brush borders isolated from the proximal half of the intestine when these proximal brush borders were preincubated with supernatant fluid obtained after centrifugation of homogenates of distal intestinal mucosa at 28,500 g. The factor in this supernate responsible for the effect on proximal brush borders was shown to be particulate in nature upon centrifugation at speeds of 54,500 g or greater. The resultant pellet contained ribosomes and membranous fragments. Prolonged incubation of brush borders with crude saline extracts of hamster gastric mucosa resulted in decreased uptake of B(12)-(57)Co and marked lysis of brush borders with concomitant release of tissue nitrogen. Neither lysis of brush borders nor decreased uptake of B(12)-(57)Co with prolonged incubation was observed when hamster IF was partially purified. Furthermore, uptake of B(12)-(57)Co by brush borders increased with increasing purity of the IF preparation used. These results demonstrate IF-mediated attachment of B(12)-(57)Co to brush borders and microvillous membranes of hamster intestinal cells and provide further support for the presence of a specific receptor for IF-bound vitamin B(12) at the microvillous surface of the intestinal cell. IF-mediated attachment to the intestinal cell surface appears to be facilitated by divalent cations and to result from adsorption rather than an energy-requiring enzymatic reaction. Crude sources of hamster IF contain a factor which causes lysis of brush borders in vitro and which may explain in part the inhibitory effects of IF excess previously observed in vitro.
仓鼠内因子（IF）制剂能显著增强从仓鼠肠道远端而非近端绒毛吸收细胞分离得到的刷状缘和微绒毛膜对（57）钴标记的氰钴胺素（B（12）-（57）Co）的摄取。在大鼠和兔的IF制剂中也观察到了类似的效果，但从人、狗和猪获得的IF制剂则无效。通过凝胶过滤或离子交换色谱对仓鼠IF制剂进行分级分离后，各组分增强刷状缘对B（12）-（57）Co摄取的程度与该组分的维生素B（12）结合能力密切相关。IF介导的B（12）-（57）Co与刷状缘的结合迅速发生，孵育介质中去除葡萄糖或氧气不会使其减弱，当孵育温度从37℃降至7℃时也没有明显改变。然而，在没有二价阳离子的情况下，摄取量会显著降低。当从近端肠道分离的刷状缘与经28,500g离心的远端肠黏膜匀浆上清液预孵育时，仓鼠IF制剂能增强其对B（12）-（57）Co的摄取。经54,500g或更高速度离心后，该上清液中对近端刷状缘有作用的因子显示为颗粒状。所得沉淀含有核糖体和膜碎片。用仓鼠胃黏膜粗盐水提取物长时间孵育刷状缘会导致B（12）-（57）Co摄取减少以及刷状缘明显裂解，并伴随组织氮的释放。当仓鼠IF部分纯化后，长时间孵育既未观察到刷状缘裂解，也未观察到B（12）-（57）Co摄取减少。此外，刷状缘对B（12）-（57）Co的摄取随着所用IF制剂纯度的提高而增加。这些结果证明了IF介导的B（12）-（57）Co与仓鼠肠道细胞刷状缘和微绒毛膜的结合，并为肠细胞微绒毛表面存在IF结合维生素B（12）的特异性受体提供了进一步的支持。IF介导的与肠细胞表面的结合似乎受到二价阳离子的促进，是由吸附而非需要能量的酶促反应导致的。仓鼠IF的粗制品中含有一种在体外会导致刷状缘裂解的因子，这可能部分解释了先前在体外观察到的IF过量的抑制作用。
