In enzymology, a luteolin O-methyltransferase is an enzyme that catalyzes the chemical reaction S-adenosyl-L-methionine + 5,7,3',4'-tetrahydroxyflavone ⇌ {\displaystyle \rightleftharpoons } S-adenosyl-L-homocysteine + 5,7,4'-trihydroxy-3'-methoxyflavoneThus, the two substrates of this enzyme are S-adenosyl methionine and 5,7,3',4'-tetrahydroxyflavone, whereas its two products are S-adenosylhomocysteine and 5,7,4'-trihydroxy-3'-methoxyflavone. Wikipedia