Fig. 2. AR27/IRP1 has reduced c-aconitase activity. Strains 0615d/IRP1 and AR27/IRP1 were grown in SD-ura medium to an OD₆₀₀ of 0.8, and cells were harvested and extracts prepared as described previously (Brown et al., 1998). Extracts were used to measure endogenous c-aconitase activity (A), IRP1 protein by immunoblotting (B), or were incubated with 0.5 mM ferrous ammonium sulfate and 50 mM DTT at room temperature for 1 h to activate c-aconitase followed by aconitase assay (C). Unit activity is in µmol cis-aconitate produced per min per mg total extract protein using 20 mM isocitrate as substrate (Kennedy et al., 1983). The results of the enzyme assays are representative of three independent experiments.