Distribution of iron in reticulocytes after inhibition of heme synthesis with succinylacetone: examination of the intermediates involved in iron metabolism.
Succinylacetone (SA) is an inhibitor of heme synthesis that acts on the enzyme delta-aminolevulinic acid dehydratase. When reticulocytes are incubated with 59Fe-transferrin (59Fe-Tf) in the presence of SA, there is an accumulation of 59Fe in the mitochondrion and in a cytosolic non-heme intermediate that has been described as a putative Fe transporter (Adams et al, Biochim Biophys Acta 1012:243, 1989). Considering these observations, the present study was designed to examine the intermediates of Fe metabolism in control and SA-treated reticulocytes. This investigation showed that in the cytosol of control cells, most 59Fe was incorporated into hemoglobin (Hb) with a minor amount entering ferritin. In addition, a previously unrecognized cytosolic intermediate was identified (band X) that was absent when heme synthesis was inhibited with SA. Upon reincubation of SA-treated reticulocytes with protoporphyrin IX, band X initially increased in intensity and then decreased later in the incubation. In contrast, when 59Fe-labeled control cells were reincubated in the presence of SA and unlabeled diferric Tf, there was a marked decrease in the intensity of band X. These experiments suggest that component X may be an intermediate involved in the transfer of heme in the cytosol. Alternatively, these data could also be interpreted as indicating that band X may be a short-lived hemoprotein. We have confirmed the presence of an 59Fe-containing molecule in the cytosol of SA-treated reticulocytes (band Y) that is not present in control cells. However, when cells were incubated with 59Fe-Tf plus SA and then chased in the presence of SA and unlabeled diferric Tf, there was no decrease in this cytosolic pool of Fe, suggesting that it was not a intermediate supplying Fe for either ferritin or heme synthesis. Finally, there is little low molecular weight (Mr) Fe in reticulocytes, and our studies suggest that the low-Mr Fe present does not behave as an intermediate. Moreover, after inhibition of heme synthesis with SA, 59Fe in the low-Mr compartment was markedly decreased, suggesting that this component may be heme or a low-Mr heme-containing molecule. Considering the apparent lack of a cytosolic Fe transporter in rabbit reticulocytes, an alternative model of intracellular Fe transport is proposed that does not implicate a potentially toxic intermediate pool of low-Mr Fe complexes.
Richardson
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Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada.
Ponka
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Vyoral
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D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D002451:Cell Compartmentation; D003600:Cytosol / Q000378:metabolism; D003676:Deferoxamine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006418:Heme / Q000096:biosynthesis*; D006454:Hemoglobins / Q000096:biosynthesis; D006537:Heptanoates / Q000494:pharmacology*; D007501:Iron / Q000032:analysis* / Q000378:metabolism; D007502:Iron Chelating Agents / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D000623:Porphobilinogen Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011524:Protoporphyrins / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000737:chemistry* / Q000187:drug effects / Q000648:ultrastructure; D014168:Transferrin / Q000378:metabolism
D001798:Blood Proteins; D004791:Enzyme Inhibitors; D006454:Hemoglobins; D006537:Heptanoates; D007502:Iron Chelating Agents; D008565:Membrane Proteins; D011524:Protoporphyrins; D014168:Transferrin; D006418:Heme; C020804:succinylacetone; D007501:Iron; D000623:Porphobilinogen Synthase; D003676:Deferoxamine