Kinetic Studies of Ferrous Ion Oxidation with Crystalline Human Ferroxidase (Ceruloplasmin)

The kinetics of the catalysis of Fe(II) oxidation by crystalline human ferroxidase (ceruloplasmin) has been studied under various conditions at 30°. Two Km values with respect to Fe(II), Km1 = 0.6 µm and Km2 = 50 µm, were obtained at pH 6.5, at which ferroxidase gave the maximum activity of 550 Fe(II) per ferroxidase per min in an acetate buffer. Competition between the two substrates, p-phenylenediamine and Fe(II), was observed. The stoichiometry of Fe(II), ferroxidase, and oxygen, determined from the experimental data, was 4:1:1.