The enzyme methionine γ-lyase (EC 4.4.1.11, MGL) is in the γ-family of PLP-dependent enzymes. It degrades sulfur-containing amino acids to α-keto acids, ammonia, and thiols: L-methionine + H2O = methanethiol + NH3 + 2-oxobutanoate (overall reaction)(1a) L-methionine = methanethiol + 2-aminobut-2-enoate(1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous)(1c) 2-iminobutanoate + H2O = 2-oxobutanoate + NH3 (spontaneous) Because sulfur-containing amino acids play a role in multiple biological processes, the regulation of these amino acids is essential. Additionally, it is crucial to maintain low homocysteine levels for the proper functioning of various pathways and for preventing the toxic effects of the cysteine homologue. Methionine γ-lyase has been found in several bacteria (Clostridiums porogenes, Pseudomonas ovalis, Pseudomonas putida, Aeromonas sp., Citrobacter intermedius, Brevibacterium linens, Citrobacter freundii, Porphyromonas gingivalis, Treponema denticola), parasitic protozoa (Trichomonas vaginalis, Entamoeba histolytica), and plants (Arabidopsis thaliana). This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is L-methionine methanethiol-lyase (deaminating; 2-oxobutanoate-forming). Other names in common use include L-methioninase, methionine lyase, methioninase, methionine dethiomethylase, L-methionine γ-lyase, and L-methionine methanethiol-lyase (deaminating). This enzyme participates in . It employs one cofactor, pyridoxal phosphate. (en)