In enzymology, an androst-4-ene-3,17-dione monooxygenase is an enzyme that catalyzes the chemical reaction androst-4-ene-3,17-dione + AH2 + O2 ⇌ {\displaystyle \rightleftharpoons } 3-oxo-13,17-secoandrost-4-ene-17,13alpha-lactone + A + H2OThe 3 substrates of this enzyme are androst-4-ene-3,17-dione, an electron acceptor AH2, and O2, whereas its 3 products are 3-oxo-13,17-secoandrost-4-ene-17,13alpha-lactone, the reduction product A, and H2O. Wikipedia