Methylquercetagetin 6-O-methyltransferase

S-adenosyl-L-methionine + 5,6,3',4'-tetrahydroxy-3,7-dimethoxyflavone $\rightleftharpoons$ S-adenosyl-L-homocysteine + 5,3',4'-trihydroxy-3,6,7-trimethoxyflavone

Thus, the two substrates of this enzyme are S-adenosyl methionine and 5,6,3',4'-tetrahydroxy-3,7-dimethoxyflavone, whereas its two products are S-adenosylhomocysteine and 5,3',4'-trihydroxy-3,6,7-trimethoxyflavone.

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:3',4',5,6-tetrahydroxy-3,7-dimethoxyflavone 6-O-methyltransferase. Other names in common use include flavonol 6-O-methyltransferase, flavonol 6-methyltransferase, 6-OMT, S-adenosyl-L-methionine:3',4',5,6-tetrahydroxy-3,7-dimethoxyflavone, and 6-O-methyltransferase.

References

De Luca V, Ibrahim RK (1985). "Enzymatic synthesis of polymethylated flavonols in Chrysosplenium americanum. I. Partial purification and some properties of S-adenosyl-L-methionine:flavonol 3-, 6-, 7-, and 4'-O-methyltransferases". Arch. Biochem. Biophys. 238 (2): 596–605. doi:10.1016/0003-9861(85)90205-X. PMID 3994393.
De Luca V, Ibrahim RK (1985). "Enzymatic synthesis of polymethylated flavonols in Chrysosplenium americanum. II. Substrate interaction and product inhibition studies of flavonol 3-, 6-, and 4'-O-methyltransferases". Arch. Biochem. Biophys. 238 (2): 606–18. doi:10.1016/0003-9861(85)90206-1. PMID 3994394.