Intrinsic factor-mediated attachment of vitamin B12 to brush borders and microvillous membranes of hamster intestine.
Intrinsic factor-mediated attachment of vitamin B12 to brush borders and microvillous membranes of hamster intestine.
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内在因素介导的维生素 B12 与仓鼠肠道刷状缘和微绒毛膜的附着。
DOI：
10.1172/jci105615
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发表时间：
1967
期刊：
影响因子：
--
通讯作者：
J. S. Trier
中科院分区：
文献类型：
--
作者：
R. Donaldson;I. L. Mackenzie;J. S. Trier
从仓鼠肠的远侧而非近侧的绒毛吸收细胞中分离的刷状缘和微绒毛膜，可显著增强（57）钴标记的氰钴胺（B（12）-（57）Co）的摄取。用大鼠和兔IF制剂观察到类似的效果，但从人、犬和猪获得的IF制剂无效。通过凝胶过滤或离子交换色谱法分离仓鼠IF制剂后，各组分增强刷状缘对B（12）-（57）Co摄取的程度与组分的维生素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，从培养介质中去除葡萄糖或氧气不会减弱，当培养温度从37 ℃降至7 ℃时也不会显著改变。然而，在没有二价阳离子的情况下，摄取量明显减少。当这些近端刷状缘与远端肠粘膜匀浆在28，500 g下离心后获得的上清液预孵育时，增强了从近端一半肠分离的刷状缘对B（12）-（57）Co的摄取。在以54，500 g或更高的速度离心时，该上清液中对近端刷状缘产生影响的因子显示为微粒性质。所得沉淀物含有核糖体和膜片段。刷状缘与仓鼠胃粘膜的生理盐水粗提物长时间孵育导致B（12）-（57）Co摄取减少，刷状缘明显溶解，同时释放组织氮。当仓鼠IF部分纯化时，既没有观察到刷状缘溶解，也没有观察到随着孵育时间的延长而降低的B（12）-（57）Co摄取。此外，刷状缘对B（12）-（57）Co的吸收随所用IF制剂纯度的增加而增加。这些结果证明了IF介导的B（12）-（57）Co与仓鼠肠细胞刷状缘和微绒毛膜的附着，并进一步支持了肠细胞微绒毛表面存在IF结合维生素B（12）的特异性受体。IF介导的附着到肠细胞表面似乎是由二价阳离子促进的，并且是由吸附而不是需要能量的酶促反应引起的。仓鼠IF的粗品来源含有一种因子，该因子可导致体外刷状缘溶解，这可能部分解释先前在体外观察到的IF过量的抑制作用。
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.