In enzymology, a steroid 17alpha-monooxygenase is an enzyme that catalyzes the chemical reaction a steroid + AH2 + O2 ⇌ {\displaystyle \rightleftharpoons } a 17alpha-hydroxysteroid + A + H2OThe 3 substrates of this enzyme are steroid, an electron acceptor AH2, and O2, whereas its 3 products are 17alpha-hydroxysteroid, the reduction product A, and H2O. Wikipedia