Multifunctional blue, copper-binding (6-7 atoms per molecule) glycoprotein. It has ferroxidase activity oxidizing Fe(2+) to Fe(3+) without releasing radical oxygen species. It is involved in iron transport across the cell membrane (PubMed:16150804). Copper ions provide a large number of enzymatic activites. Oxidizes highly toxic ferrous ions to the ferric state for further incorporation onto apo- transferrins, catalyzes Cu(+) oxidation and promotes the oxidation of biogenic amines such as norepinephrin and serotonin (PubMed:14623105, PubMed:4643313, PubMed:5912351). Provides Cu(2+) ions for the ascorbate-mediated deaminase degradation of the heparan sulfate chains of GPC1 (By similarity). Has glutathione peroxidase-like activity, can remove both hydrogen peroxide and lipid hydroperoxide in the presence of thiols (PubMed:10481051). Acts as an inhibitor of the peroxidase activity of MPO (By similarity). Also shows NO-oxidase and NO2 synthase activities that determine endocrine NO homeostasis (PubMed:16906150). {ECO:0000250|UniProtKB:P13635, ECO:0000250|UniProtKB:Q61147, ECO:0000269|PubMed:10481051, ECO:0000269|PubMed:14623105, ECO:0000269|PubMed:16150804, ECO:0000269|PubMed:16906150, ECO:0000269|PubMed:4643313, ECO:0000269|PubMed:5912351}. This is the function of Ensembl gene identifier ENSG00000047457 (CP, ceruloplasmin).