The ligands that bind iron and heme in reticulocyte and may regulate their distribution are not known. Guinea pig reticulocyte hemolysates were labeled with 59Fe and filtered through molecular weight sieving columns. 59Fe-containing peaks of ferritin, transferrin, and hemoglobin were identified, as well as a low molecular weight peak containing predominantly nonheme iron, and a 17,000 mol wt heme containing peak with a specific activity (59Fe/heme) 20-fold greater than hemoglobin. We note that the low molecular weight peak, the existence of which has been postulated, has been identified for the first time without the addition of a chelating agent. We speculate that the 17,000 mol wt peak is an alpha-chain pool.

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