In enzymology, a cholesterol 25-hydroxylase is an enzyme that catalyzes the chemical reaction cholesterol + AH2 + O2 ⇌ {\displaystyle \rightleftharpoons } 25-hydroxycholesterol + A + H2OThe 3 substrates of this enzyme are cholesterol, an electron acceptor AH2, and O2, whereas its 3 products are 25-hydroxycholesterol, the reduction product A, and H2O. Wikipedia