In enzymology, a precorrin-4 C11-methyltransferase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are S-adenosyl methionine and precorrin 4; its two products are S-adenosylhomocysteine and precorrin 5.
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:precorrin-4 C11 methyltransferase. Other names in common use include precorrin-3 methylase, and CobM. It is part of the biosynthetic pathway to cobalamin (vitamin B<sub>12</sub>) in aerobic bacteria.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes and .