In enzymology, a precorrin-6Y C5,15-methyltransferase (decarboxylating) () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are S-adenosyl methionine and precorrin 6Y; its three products are S-adenosylhomocysteine, precorrin 8X, and CO<sub>2</sub>.
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:1-precorrin-6Y C5,15-methyltransferase (C-12-decarboxylating). Other names in common use include precorrin-6 methyltransferase, precorrin-6Y methylase and CobL. This enzyme is part of the biosynthetic pathway to cobalamin (vitamin B<sub>12</sub>) in aerobic bacteria.