Why is iron transported across membranes in the ferrous form?

Question

Iron in the diet of animals is predominantly in the ferric form, but it must be reduced to the ferric form by a specific ferrireductase before it can be transported across the cell membrane into the cell:

To be absorbed, dietary iron… must be in its ferrous Fe²⁺ form. A ferric reductase enzyme on the enterocytes’ brush border, duodenal cytochrome B (Dcytb), reduces ferric Fe³⁺ to Fe²⁺. A protein called divalent metal transporter 1 (DMT1), which can transport several divalent metals across the plasma membrane, then transports iron across the enterocyte’s cell membrane into the cell.

(https://en.wikipedia.org/wiki/Human_iron_metabolism)

Why is this necessary?

Answer 1

This is not my subject, but from scanning the introductions to a couple of reviews on the general topic of iron metabolism, the following factors seem to be important:

• Ferric iron is less soluble than ferrous iron [1].

• Ferric iron is potentially toxic in the cell because it can be reduced by oxygen, giving reactive oxygen species which are dangerous to the cell [2].

[1] Srai et al. (2002)

[2] Kaplan (2002)