Iron transport activity of wild-type and mutant forms of Nramp2. HEK293T cells were transfected with the constructs indicated and uptake of ⁵⁵Fe (in pmol) was measured. Cells were incubated for 20 minutes in pH 6.0 incubation buffer with 50 μmol/L ascorbate and 1 μmol/L ⁵⁵Fe-NTA. (−) Indicates iron uptake by cells transfected with an antisense control, in which the murine Nramp2 cDNA was subcloned into pMT2 in a noncoding orientation.