Effects of Baf and SA on the use of endosomal ⁵⁹Fe for heme synthesis. Endosomal vesicles were loaded with ⁵⁹Fe as described in Figure 1, and the cells were incubated at 37°C for the indicated time intervals. Baf (A) or SA (B) was included during the last 30 minutes of period 4 (Figure 1) and the entire period 5 (Figure 1) where indicated. The values are displayed as the percentage of the total cellular ⁵⁹Fe as it was after the membrane-associated radioiron was displaced by ⁵⁶Fe-Tf (Figure 1, end of period 4).