ROLE OF IRON IN OXIDASE ACTIVITY OF CERULOPLASMIN

Trace iron has been found to be associated with ceruloplasmin (ferroxidase)*** *** The name ferroxidase (ferro:O2 oxidoreductase) has been suggested on the basis of its principal naturally occurring substrates16. and the sodium acetate buffers used in test systems even after attempts to purify these substances by chromatography on Chelex-100 and Amberlite CG-50 columns. The concentration of iron eluted with ceruloplasmin from Chelex-100 columns was estimated to be as high as 10-8 M. The amount of 59Fe eluted with ceruloplasmin increases proportionally with ceruloplasmin concentration. Ceruloplasmin, pre-equilibrated with 59Fe, was dialyzed against apotransferrin, reducing the iron concentration to less than 10-8 M and the molecular activity for ascrobate to less than 1. Several previously reported substrates of ceruloplasmin were investigated with respect to the role of iron in the catalytic process. The reported substrates have now been classified into three groups: 1. 1.Fe(II), which is oxidized directly by ceruloplasmin. 2. 2.Certain aryldiamines and polyphenols: e.g., p-phenylenediamine and its methyl derivatives, epinephrine, norepinephrine, dopamine, and serotonin, for which oxidation is not completely inhibited by iron chelators, are directly oxidized by the enzyme. However, the rates of oxidation of most of these substrates can be increased by iron via a Fe(II)-ceruloplasmin coupled reaction. 3. 3.Numerous compounds which reduce Fe(III); e.g., ascorbate, hydroquinone, catechol, hydroxylamine, thioglycolate, cysteine, ferro cyanide, and DOPA, for which oxidation is completely inhibited by iron chelators, appear not to be directly oxidized by the enzyme. Therefore, they must function in an iron-ceruloplasmin coupled reaction and the iron-dependent substrates. The inhibition of the oxidation of these iron coupled substrates by apotransferrin and citrate is due to their strong chelaton of Fe(III). © 1968.