The relationship between heme synthesis and iron uptake in erythroid cells.

Hemin inhibited 59Fe uptake from transferrin (Tf) by mouse erythro-leukemia cells (MELC) induced for differentiation by hexamethylene bisacetamide (HMBA), but the rate and the extent of 125I-Tf endocytosis was unaffected. Hemin inhibited 59Fe incorporation into heme by a greater proportion than the overall uptake of 59Fe from Tf. Desferrioxamine (DFO) reverted the inhibition of 59Fe transport into MELC caused by hemin. Exogenous 5-aminolevulinic acid (ALA) stimulated 59Fe utilization for heme synthesis in MELC but did not revert inhibition induced by hemin. No evidence for a direct effect of heme on the Tf cycle or iron release was found.