In enzymology, an O-acetylhomoserine aminocarboxypropyltransferase (EC 2.5.1.49) is an enzyme that catalyzes the chemical reaction

O-acetyl-L-homoserine + methanethiol ${\displaystyle \rightleftharpoons }$ L-methionine + acetate

Thus, the two substrates of this enzyme are O-acetyl-L-homoserine and methanethiol, whereas its two products are L-methyionine and acetate.

This enzyme belongs to the family of transferases, specifically those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is O-acetyl-L-homoserine:methanethiol 3-amino-3-carboxypropyltransferase. Other names in common use include O-acetyl-L-homoserine acetate-lyase (adding methanethiol), O-acetyl-L-homoserine sulfhydrolase, O-acetylhomoserine (thiol)-lyase, O-acetylhomoserine sulfhydrolase, and methionine synthase. This enzyme participates in methionine metabolism and cysteine metabolism.