Transferrin-bound iron uptake by nm/nm reticulocytes. Reticulocyte iron uptake and heme synthesis was measured in 129S6/SvEvTac-?/+ (n = 10) and -nm/nm (n = 5) as well as MK/ReJ-Slc11a2^mk/+ (n = 4) and -Slc11a2^mk/mk (n = 9) animals following incubation with ⁵⁵Fe₂-transferrin. Error bars are of total iron uptake ± 1 SD. Incubations were carried out for 30 minutes, when the assay was linear, but normalized to and presented as uptake per microgram of RNA per hour.