Acetobacterium dehalogenans (Strain MC)is a strictly anaerobic homoacetogenic bacterium which converts methyl-groups of methylchloride or phenylmethylethers into acetate in its energy meta-bolism. The inducible enzyme O-demethylase catalyzes the cleavage of the ether bond of phenyl-methyl-ethers and the transfer of the methylgroup to tetra-hydrofolate (FH4). O-demethylase purified with 4-hydroxy-3-methoxybenzoate (vanillate) as methyl donor consists of four individual proteins: A corrinoid protein (OdmA) is me-thylated with vanillate by methyltransferase I. The methylgroup is then transferred to FH4 by methyltranferase II. The activating enzyme catalyzes the ATP-dependent reduction of the catalytically inactive cob(II)alamin form of OdmA with electrons from hydrogen.