Divalent metal transporter role

Divalent metal transporter 1 was identified in the enterocytes of the small intestine and in other cells as a proton symporter, favoring the transport from more acidic media, and it was assigned a major role in the assimilation of iron from the animal diet [54]. But its lack of selectivity in reconstituted systems soon became apparent, showing that Cd " is efficiently transported by DMTl in vitro [54,55]. This observation was extended to include a correlation of DMTl expression and Cd " transport, both in cellular models [56-58] and in animals with iron-manipulated diets [59,60]. Furthermore, animal [61], and human [62] studies comparing iron status and cadmium burden fully corroborated the association of Cd " transport with the plasma membrane form(s) of DMTl. Hence, there is no doubt that DMTl transports Cd " in cells that produce this transporter. This conclusion is relevant to an individual s susceptibility to cadmium toxicity since DMTl is strongly iron-regulated and cadmium transport thus depends on the nutritional and (patho)physiological iron status, in particular for intestinal absorption. 

The transferrin receptor TfR may have a role in reduction of the transferrin-bound Fe(III) within the endosome. Iron leaves the endosome to enter the cytoplasm via the divalent metal ion transporter DMTl, which only transports Fe(ll), not Fe(lll) (see Section 5). As noted above, the reduction potential of Fe(lll) bound to transferrin not associated with TfR is less than -500 mV, which is too low for reduction of the bound Fe(lll) by physiological systems such as reduced pyridine nucleotides. However, as Dhungana et al. have shown," the reduction potential of Fe(III)-transferrin bovmd to TfR is considerably higher at around -300 mV, which puts it in the range for reaction with physiological reductants. 

The role of the iron in electron transport is still obscure. Electron transfer from the first to the second quinone acceptor in Fe-depleted RC is only a factor of two slower than in Fe-containing RC [34]. Fe can be replaced by other divalent metals without much affecting the lifetime of Q [34]. The iron may stabilize the semi-... 

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