Specialised copper sites have been recruited during evolution to provide long-range electron transfer reactivity and oxygen binding and activation in proteins destined to cope with oxygen reactivity in different organisms. Ceruloplasmin is an ancient multicopper dase evolved to insure a safe handling of oxygen in some metabolic pathways of vertebrates. The presently available knowledge of its structure provides a glimpse of its plasticity, revealing a multitude of binding sites that point to an elaborate mechanism of multifunctional activity. Ceruloplasmin represents an example of a 'moonlighting' protein that overcomes the one gene-one structure-one function concept to follow the changes of the organism in its physiological and pathological conditions.