In enzymology, a columbamine oxidase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are columbamine and O<sub>2</sub>, whereas its two products are berberine and H<sub>2</sub>O.
This enzyme belongs to the family of oxidoreductases, specifically those acting on X-H and Y-H to form an X-Y bond with oxygen as acceptor. The systematic name of this enzyme class is columbamine:oxygen oxidoreductase (cyclizing). This enzyme is also called berberine synthase. This enzyme participates in alkaloid biosynthesis i. It employs one cofactor, iron.