Cytochromes P450 are a superfamily of monooxygenases that are found in all kingdoms of life and which show extraordinary diversity in their reaction chemistry.This superfamily consists of hundreds families and several clans.The most unusual enzymes among cytochromes P450 belong to the CYP74 clan.Unlike the monooxygenases, the CYP74 enzymes have an atypical reaction mechanism that requires neither oxygen nor an NADPH-reductase.