THE MAMMALIAN TRANSFERRIN-INDEPENDENT IRON TRANSPORT-SYSTEM MAY INVOLVE A SURFACE FERRIREDUCTASE ACTIVITY
THE MAMMALIAN TRANSFERRIN-INDEPENDENT IRON TRANSPORT-SYSTEM MAY INVOLVE A SURFACE FERRIREDUCTASE ACTIVITY
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DOI：
10.1042/bj3020875
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发表时间：
1994-09-15
影响因子：
4.1
通讯作者：
KAPLAN, J
中科院分区：
文献类型：
--
作者：
JORDAN, I;KAPLAN, J
哺乳动物细胞通过转铁蛋白非依赖性铁转运系统的活性从柠檬酸铁或次氮基三乙酸铁积累铁[Sturrock，亚历山大，兰姆，克雷文和卡普兰（1990）生物化学杂志265，3139-3145]。吸收系统可能识别和运输铁离子复合物，或者细胞可以在表面还原三价铁，然后运输亚铁。为了区分这些可能性，我们将鳗鱼暴露于[Fe-59]柠檬酸铁或[C-14]柠檬酸铁，并确定铁的积累是否伴随着柠檬酸盐的强制性积累。在HeLa细胞和人类皮肤成纤维细胞中，铁的积累速率是柠檬酸盐的三到五倍。用柠檬酸铁或柠檬酸铁铵孵育成纤维细胞导致铁和柠檬酸盐的积累增强;积累的摩尔比接近统一。然而，当柠檬酸铁孵育的细胞单独暴露于[C-14]柠檬酸盐时，观察到类似的柠檬酸盐蓄积速率。进一步的研究表明，铁和柠檬酸盐的积累的独立性：除了未标记的柠檬酸盐的细胞减少标记的柠檬酸盐的摄取，而不影响Fe-59的积累;铁的摄取减少，而柠檬酸盐的摄取不受影响的亚铁螯合剂的加入;减少三价铁的抗坏血酸增加铁的摄取，但没有影响柠檬酸盐的摄取。当HeLa细胞被耗尽的钙，铁的摄取减少，但有柠檬酸盐摄取的影响不大。这些结果表明铁的运输不需要柠檬酸盐的强制性运输，反之亦然。哺乳动物转铁蛋白独立的铁转运系统出现在功能上类似于铁转运系统在细菌和植物王国，需要的活动的表面还原酶和铁金属转运蛋白。
Mammalian cells accumulate iron from ferric citrate or ferric nitrilotriacetate through the activity of a transferrin-independent iron transport system [Sturrock, Alexander, Lamb, Craven and Kaplan (1990) J. Biol. Chem. 265, 3139-3145]. The uptake system might recognize and transport ferric-anion complexes, or cells may reduce ferric iron at the surface and then transport ferrous iron. To distinguish between these possibilities we exposed eels to either [Fe-59]ferric citrate or ferric [C-14]citrate and de termined whether accumulation of iron was accompanied by the obligatory accumulation of citrate. In HeLa cells and human skin fibroblasts the rate of accumulation of iron was three to five times greater than that of citrate. Incubation of fibroblasts with ferric citrate or ferric ammonium citrate resulted in an enhanced accumulation of iron and citrate; the molar ratio of accumulation approaching unity. A similar rate of citrate accumulation: however, was observed when ferric citrate-incubated cells were exposed to [C-14]citrate alone. Further studies demonstrated the independence of iron and citrate accumulation: addition of unlabelled citrate to cells decreased the uptake of labelled citrate without affecting the accumulation of Fe-59; iron uptake was decreased by the addition of ferrous chelators whereas the uptake of citrate was unaffected; reduction of ferric iron by ascorbate increased the uptake of iron but had no effect on the uptake of citrate. When HeLa cells were depleted of calcium, iron uptake decreased, but there was little effect on citrate uptake. These results indicate that transport of iron does not require the obligatory transport of citrate and vice versa. The mammalian transferrin-independent iron transport system appears functionally similar to iron transport systems in both the bacterial and plant kingdoms which require the activities of both a surface reductase and a ferrous metal transporter.