A copper-containing protein in Chlamydomonas reinhardtii is a plasma membrane ferroxidase, encoded by the FOX1 gene, involved in Fe assimilation. FOX1 is most highly related to the mammalian homologues hephaestin and ceruloplasmin; its occurrence and pattern of expression in Chlamydomonas indicate a role for copper in iron assimilation in a photosynthetic species.