Nature 403, 298–301 (2000).

Throughout Figs 2–4 and the corresponding legends, mM should have been mmol, µM should have been µmol, and pM should have been pmol. In addition, in Fig. 3a the x axis should have been labelled ‘Fe (II) conc. in medium (µmol)’; and in Fig. 3b the x axis should have been labelled ‘Halide ion conc. in medium (mmol)’.