In enzymology, a bilirubin oxidase (EC 1.3.3.5) is an enzyme that catalyzes the chemical reaction 2 bilirubin + O2 2 biliverdin + 2 H2O. Thus, the two substrates of this enzyme are bilirubin and O2, whereas its two products are biliverdin and H2O. This enzyme belongs to the family of oxidoreductases, to be specific those acting on the CH-CH group of donor with oxygen as acceptor. This enzyme participates in porphyrin and chlorophyll metabolism.