Iron regulatory protein-1 (IRP-1) is known as a cytosolic aconitase and a central regulator of iron (Fe) homeostasis. IRP-1 regulates the expression of Fe metabolism-related proteins by interacting with the Fe-responsive element (IRE) in the untranslated regions of mRNAs of these proteins. However, it is less known whether IRP-1 modulates various non-Fe metals. In the present study, we showed that treatment of homogenously purified IRP-1 with non-Fe metals decreased the affinity to IRE in RNA band shift assays and increased aconitase activity. Non-Fe metals also inhibited Fe-55 incorporation into the fourth labile position of the Fe-S cluster of IRP-1. In PLC hepatoma cells, metal loading inactivated binding activity and activated enzyme activity. It also suppressed transferrin receptor mRNA expression in the cells. These results suggest that various non-Fe metals modulate IRP-1 by conversion of the 3Fe-4S apo-form to a [1 non-Fe metal + 3Fe]-4Fe holo-form. (C) 2002 Elsevier Science.