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Am J Physiol Gastrointest Liver Physiol 275: G279-G286, 1998;
0193-1857/98 $5.00
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Vol. 275, Issue 2, G279-G286, August 1998

Mechanisms of ferric citrate uptake by human hepatoma cells

Deborah Trinder and Evan Morgan

Department of Physiology, University of Western Australia, Nedlands 6907, Western Australia, Australia

The mechanisms of uptake of non-transferrin-bound iron by human hepatoma cells (HuH7) were investigated using 59Fe-citrate and [14C]citrate. The amount of iron associated with the cells increased linearly with time, whereas citrate uptake reached a plateau after 45 min, resulting in a cellular accumulation of iron over citrate. The cells displayed high-affinity membrane binding sites for citrate with maximum binding of 118 ± 17 pmol citrate/mg protein and a dissociation constant of 21 ± 2 µM (n = 3). Iron uptake was saturable with a maximum uptake rate of 1.95 ± 0.43 pmol · mg protein-1 · min-1 and an apparent Michaelis constant of 1.1 ± 0.1 µM. Nonradioactive ferric citrate and citrate inhibited 59Fe uptake to a similar degree. This suggests that the uptake of citrate-bound iron is dependent on either binding to specific citrate binding sites or the concentration of unbound iron. The uptake of iron was inhibited by ferricyanide (>100 µM) and ferrous iron chelators but stimulated by ferrocyanide and ascorbate, suggesting that the iron is reduced from Fe3+ to Fe2+ and transported into the cell by an iron carrier-mediated step.

non-transferrin-bound iron; iron overload; iron carrier; citrate binding sites


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