True wild type and recombinant wild type cytochrome c oxidase from Paracoccus denitrificans show a 20-fold difference in their catalase activity

► Recombinant cytochrome c oxidase produced homologously was compared to the wild type. ► The recombinant protein shows a 20-fold increase in the catalase side reaction. ► Adjusting the chaperone levels leads to a significant decrease of the catalase activity. ► Well adjusted chaperone levels are required to achieve wild type activities.