Caco-2 cells grown in bicameral chambers and depleted of serum proteins were offered 1 μmol/L ⁵⁹Fe ascorbate in the apical chamber with the basal chamber containing either 0 to 50 μmol/L apotransferrin (○) or 0 to 10 μmol/L ferri-transferrin (•). The cells were incubated at 37°C for 1 hour and the moles of⁵⁹Fe transported into the basal chamber were determined. Presented are the mean ± SD of triplicates for three experiments. When not apparent, the error bars are smaller than the symbols. The curves were fit to the data with Michaelis-Menton kinetics using nonlinear regression analysis.