Effects of halide ions on porcine kidney catalase

The inactivating effects of halide ions on porcine kidney catalase were investigated. It was found that the inactivation of catalase was dependent on incubation time with halides and on their concentrations: the addition of 2 M NaCl reduced the activity to 18% of the original level, whereas the same extent of inactivation was obtained in the presence of 0.1 M NaF. Removal of excess halide ions by dialysis resulted in good recovery of enzyme activity for all halides examined except for KI. Additions of halide ions to catalase solution caused subtle but evident alterations in the absorption and CD spectra. We could detect clear difference spectra between the salt-treated and native catalase solutions. These difference spectra showed halide concentration dependence with an evident isosbestic point. From these changes and also changes in CD spectra, we deduced that fluoride, chloride, and bromide ions can bind with heme iron of the catalase molecule as ligands to form stable catalase-halide complexes, but iodide ions showed a different reactivity with catalase from other halides and may cause gross alteration in the structure or conformation of catalase. Dissociation constants (Kd) were estimated to be 2.5, 0.23, and 26 M for chloride, fluoride, and bromide complexes with catalase, respectively, and there is no heme-heme interaction during formation of the catalase-halide complexes as estimated from the Hill plot.