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