In enzymology, a thymidylate synthase is an enzyme that catalyzes the chemical reaction 5,10-methylenetetrahydrofolate + dUMP + FADH2 ⇌ {\displaystyle \rightleftharpoons } dTMP + tetrahydrofolate + FADThe 3 substrates of this enzyme are 5,10-methylenetetrahydrofolate, dUMP, and FADH2, whereas its 3 products are dTMP, tetrahydrofolate, and FAD. Wikipedia