Evidence That Calcineurin Accommodates an Active Site Binuclear Metal Center

In this report we provide data indicating that the iron and zinc ions of native bovine brain calcineurin are present as a binuclear metal cluster, albeit in a ligand environment different from that in PAPase. Furthermore, we show that dithionite reduction of the bound ferric ion leads to loss of activity which can be quantitatively recovered upon reoxidation, indicating that the oxidation state of bound iron is important for enzymatic function. (DBO)