Nuñez M T, Glass J
J Biol Chem. 1983 Aug 25;258(16):9676-80.
Rabbit reticulocytes were pulsed for 10 s with diferric 59Fe, 125I-labeled transferrin followed without further manipulation by a chase with unlabeled diferric transferrin. The 125I-transferrin and 59Fe were measured in different cell compartments as a function of time thereafter. Immediately after binding, transferrin entered a phase that lasted 60 s, characterized by a slow dissociation of transferrin into the extracellular medium. During this period, most of the iron originally present in transferrin is donated to the cell. The half-time of 59Fe release from transferrin was 43 s. After the initial 60 s, transferrin, now devoid of iron, is released into the medium. The whole transferrin cycle lasted about 4 min. The iron released from transferrin could be transiently found in the cell plasma membrane, the cytosol, and the mitochondria. All these compartments behaved like intermediates in the iron uptake process as their 59Fe content rose, reached a plateau, and gradually fell. Finally, the iron was incorporated into heme with a half-time of incorporation of 173 s. We conclude that the release of iron from transferrin is one of the fastest events occurring after the initial binding of transferrin. The limiting step in the entire process of iron delivery is the dissociation of apotransferrin from its receptor, a step which will enable the latter to undergo another cycle of transferrin binding.
用双铁59Fe对兔网织红细胞进行10秒的脉冲处理，随后加入125I标记的转铁蛋白，接着用未标记的双铁转铁蛋白进行追踪，不再进行进一步操作。此后，随着时间的推移，在不同的细胞区室中测量125I -转铁蛋白和59Fe。结合后立即，转铁蛋白进入一个持续60秒的阶段，其特征是转铁蛋白缓慢解离到细胞外培养基中。在此期间，最初存在于转铁蛋白中的大部分铁被捐赠给细胞。转铁蛋白释放59Fe的半衰期为43秒。在最初的60秒后，现在不含铁的转铁蛋白被释放到培养基中。整个转铁蛋白循环持续约4分钟。从转铁蛋白释放的铁可短暂地在细胞质膜、胞质溶胶和线粒体中发现。所有这些区室在铁摄取过程中表现得像中间体，因为它们的59Fe含量上升、达到平台期并逐渐下降。最后，铁以173秒的掺入半衰期掺入血红素中。我们得出结论，转铁蛋白中铁的释放是转铁蛋白初始结合后发生的最快事件之一。铁传递整个过程中的限速步骤是脱铁转铁蛋白与其受体的解离，这一步骤将使后者能够经历另一个转铁蛋白结合循环。
