Demethylrebeccamycin-D-glucose O-methyltransferase (EC 2.1.1.164, RebM) is an enzyme with systematic name S-adenosyl-L-methionine:demethylrebeccamycin-D-glucose O-methyltransferase.^[1][2] This enzyme catalyses the following chemical reaction

4'-demethylrebeccamycin + S-adenosyl-L-methionine ${\displaystyle \rightleftharpoons }$ rebeccamycin + S-adenosyl-L-homocysteine

Demethylrebeccamycin-D-glucose O-methyltransferase catalyses the last step in the biosynthesis of rebeccamycin, an indolocarbazole alkaloid produced by the Actinobacterium Lechevalieria aerocolonigenes.