Molecular function

Catalysis of the reaction: S-adenosyl-L-methionine + a 3-demethylubiquinol = S-adenosyl-L-homocysteine + a ubiquinol.

OMHMB-methyltransferase, S-adenosyl-L-methionine:2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone-O-methyltransferase

Note that the polyprenyl sidechain substrate for this reaction has a different number of prenyl units in different organisms (for example, ubiquinone-6 in Saccharomyces, ubiquinone- 9 in rat and ubiquinone-10 in human), and thus the natural substrate for the enzymes from different organisms has a different number of prenyl units. However, the enzyme usually shows a low degree of specificity regarding the number of prenyl units.