Further Elucidation of the Mechanism of Iron Transport Form Plasma Transferrin to Mitochondrial Ferrochelatase: Further Evidence for the “Kiss and Run” Hypothesis
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Normal hemoglobinization of immature red blood cells (RBC) requires iron (Fe) uptake from transferrin (Tf), mediated by Tf receptors (TfR). Following the binding of Fe(III)2-Tf to TfR on the erythroid cell membrane, the Tf-TfR complexes are internalized via endocytosis, following which Fe is released from Tf by a process involving endosomal acidification and reduction by Steap3. Fe2+ is then transported across the endosomal membrane by the divalent metal transporter 1 (DMT1). Unfortunately, the post-endosomal path of Fe within cells remains elusive or is, at best, controversial. It has been commonly accepted that a low molecular weight intermediate chaperones Fe in transit from endosomes to mitochondria and other sites of utilization; however, this much sought Fe binding intermediate has never been identified.