So far, Co has been mainly studied in its role associated to the corrin ring of B 12 but there are other Co-containing proteins like methionine aminopeptidase, prolidase, nitrile hydratase, glucose isomerase, methylmalonyl-CoA carboxytransferase, aldehyde decarbonylase, lysine-2,3-aminomutase, and bromoperoxidase (Kobayashi and Shimizu, 1999).
Source: wiktionary