Iron Imports. II. Iron uptake at the apical membrane in the intestine.

How does iron enter enterocytes? Ablating SLC11A2, the gene for the divalent metal ion transporter DMT1, supports evidence from the Belgrade rat and mk mouse models establishing DMT1 as the primary mechanism serving apical uptake of nonheme iron. DMT1 harnesses the energy from the proton electrochemical potential gradient to drive active transport of Fe(2+) (and perhaps Mn(2+) and other metal ions) into enterocytes. Fe(III) must first be reduced by ascorbic acid and surface ferrireductases. Among these is duodenal cytochrome B (DcytB), but lack of an obvious phenotype in DcytB (Cybrd1) knockout mice suggests ferrireductase redundancy. Our understanding of heme absorption has lagged, but the time is ripe for gains.