Cops and robbers: Putative evolution of copper oxygen-binding proteins

Two closely related copper proteins, phenoloxidase and haemocyanin, are kno wn to be involved in different physiological functions such as the primary immune response and oxygen transport. Although the proteins differ structur ally, they have the same active site by which dioxygen is bound. Recent res ults reveal that haemocyanin also exhibits phenoloxidase activity. A scenar io is proposed for the evolutionary relationships among copper oxygen-bindi ng proteins (COPs).