Transferrin-iron routing to the cytosol and mitochondria as studied by live and real-time fluorescence

Biochem J. 2010 Jul 1;429(1):185-93. doi: 10.1042/BJ20100213.


In the present study we analysed the mechanism of intracellular routing of iron acquired by erythroid cells via receptor-mediated endocytosis of Tf-Fe [Tf (transferrin)-iron]. Using real-time fluorimetry and flow cytometry, in conjunction with targeted fluorescent metal sensors, we monitored concurrently the cytosolic and mitochondrial changes in labile iron evoked by endocytosed Tf-Fe. In K562 human erythroleukaemia cells, most of the Tf-Fe was found to be delivered to the cytosolic labile iron pool by a saturable mechanism [60-120 nM Km (app)] that was quantitatively dependent on: Tf receptor levels, endosomal acidification/reduction for dislodging iron from Tf and ensuing translocation of labile iron into the cytosolic compartment. The parallel ingress of iron to mitochondria was also saturable, but with a relatively lower Km (app) (26-42 nM) and a lower maximal ingress per cell than into the cytosol. The ingress of iron into the mitochondrial labile iron pool was blocked by cytosol-targeted iron chelators, implying that a substantial fraction of Tf-Fe delivered to these organelles passes through the cytosol in non-occluded forms that remain accessible to high-affinity ligands. The present paper is the first report describing intracellular iron routing measured in intact cells in real-time and in quantitative terms, opening the road for also exploring the process in mixed-cell populations of erythroid origin.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Computer Systems*
  • Cytosol / chemistry
  • Cytosol / metabolism*
  • Endocytosis / physiology
  • Fluorescence
  • Fluorometry* / methods
  • Humans
  • Iron / analysis
  • Iron / metabolism*
  • K562 Cells
  • Mitochondria / chemistry
  • Mitochondria / metabolism*
  • Transferrin / analysis
  • Transferrin / metabolism*


  • Transferrin
  • Iron