The bacteriochlorophyll biosynthesis gene, bchM, of Rhodobacter sphaeroides encodes S-adenosyl-L-methionine: Mg protoporphyrin IX methyltransferase.

The bchM gene of Rhodobacter sphaeroides has been sequenced and then overexpressed in E. coli producing a protein of M(r) approximately. 27,500. Cell-free extracts of the transformed E. coli strain are able to methylate added Mg protoporphyrin, resulting in the formation of Mg protoporphyrin monomethyl ester. The identity of this product was verified by HPLC. The bchM gene product is therefore assigned to the methyltransferase step in bacteriochlorophyll biosynthesis.