methyltransferase activity O-methyltransferase activity https://github.com/geneontology/go-ontology/issues/25591 Reactome:R-HSA-5578717 Reactome:R-HSA-5629237 Reactome:R-HSA-5629203 Catalysis of the transfer of a methyl group to the oxygen atom of an acceptor molecule. molecular_function Reactome:R-HSA-6790907 GO:0008171 Reactome:R-HSA-5629218