The Inhibition of Ferroxidase by Trivalent and Other Metal Ions

The inhibitory effects of trivalent and other metal ions on ferroxidase (ceruloplasmin EC 1.12.3.1.) activity were investigated. All trivalent cations tested inhibited ferroxidase activity but the strongest inhibitors had an ionic radius of 0.81 A or less. The inhibition by Al(III) was found to be mixed competitive and uncompetitive with respect to the substrate, Fe(II). The uncompetitive feature of the inhibition was not due to competition by Al(III) with the other substrate, oxygen. A mechanism for the mixed inhibition by Al(III) is proposed consistent with these results. A comparison of the strong cationic inhibitors provides the following metal ion series in order of decreasing effectiveness of inhibition: In(III) g ZrO(II) g Al(III) g Sc(III) g Ga(III)