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Posttranscriptionally IRP1 regulates the expression of proteins involved in the maintenance of homeostasis in mammals Fe ions . IRP1 is a bifunctional protein that occurs in the cytoplasm of aconitase , an enzyme containing a catalytic [ 4Fe -4S ] ( holo - IRP1 ) or trans - regulatory protein , devoid of the center (apo - IRP1 ) . Two IRP1 activity are mutually exclusive and are inversely regulated by Fe ions contained in the LIP , the labile iron pool . Fe ion deficiency in apo - cell IRP1 predominates , that attaches IREs iron responsive elements present in ferritin subunit mRNA (Ft ) and transferrin receptor ( TfR ) . When IRP1 binds to the 5 IRE Ft UTR subunit mRNA inhibits translation thereof . Binding of IRP1 to IRE in the 3 UTR of TfR mRNA increases its stability and, consequently, the synthesis of the receptor. The inverse regulation of synthesis of both proteins and the absence of binding of holo- IRP1 IRE occurs when the cell is high level of LIP . Both deficiency and excess of Fe effect of regulating the synthesis of Ft and TfR by IRP1 is a rapid return to physiological levels of LIP . Nitric oxide (NO) , described as the second- ion Fe biological factor regulating IRP1 activity . Similarly to iron chelators , NO inhibits aconitase activity and induces IRP1 IRE-binding . Rapid emergence of apo - IRP1 in cells exposed to NO , however , in contrast to iron , the effect of the interaction of NO with [ 4Fe -4S ] , the removal of destabilization and IRP1 molecule . Besides modulating the activity of IRP1 , NO also reduces IRP1 level in the cells.
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Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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