 They demonstrated that recombinant human hephaestin (rhHp) bound copper (determined by inductively coupled plasma mass spectrometry) and exhibited an absorption maximum at ~610 nm consistent with other blue multicopper oxidases such as ceruloplasmin.By using ferrous ammonium sulfate as a substrate, rhHp was shown to have ferroxidase activity with a Km of 2.1 μM for Fe(II).Hephaestin is a member of the family of copper oxidases that includes mammalian ceruloplasmin, yeast fet3 and fet5, and bacterial ascorbate oxidase, among others.