Isoflavone 4'-O-methyltransferase (EC 2.1.1.46) is an enzyme that catalyzes a general chemical reaction that adds a methyl group to a specific phenolic oxygen in isoflavones, for example:
In this example, the methylation reaction converts daidzein to formomonetin. The methyl group comes from the cofactor, S-adenosyl methionine (SAM), which becomes S-adenosyl-L-homocysteine (SAH). The enzyme can act on other isoflavones such as genistein but flavanones such as naringenin are not substrates. 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:isoflavone 4'-O-methyltransferase. Other names in common use include 4'-hydroxyisoflavone methyltransferase, isoflavone methyltransferase, and isoflavone O-methyltransferase.
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