FIG. 3.

Copper regulation of ferric reductase. Cells were grown in LIM + 15 μM Fe(III) with no copper (--) or with 15 μM CuSO₄ (Cu). Ferric reductase was measured as described for Fig. 1. Reductase was assayed every 2 h in exponential phase; each bar represents the peak of activity for each strain (mean ± standard deviation). The peaks occurred at the following time points in the absence and presence of Cu, respectively: WT, 2 and 0 h; frr1⁶⁰⁶, 0 and 2 h; frr2⁶⁰⁸, 6 and 6 h; frr3⁶³², 12 and 2 h; frr4⁶¹⁶, 4 and 2 h.