Reaction: 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)
For diagram click here.
Other name(s): L-methioninase; methionine lyase; methioninase; methionine dethiomethylase; L-methionine γ-lyase; L-methionine methanethiol-lyase (deaminating)
Systematic name: L-methionine methanethiol-lyase (deaminating; 2-oxobutanoate-forming)
Comments: A pyridoxal-phosphate protein. The enzyme cleaves a carbon-sulfur bond, releasing methanethiol and an unstable enamine product that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form 2-oxobutanoate and ammonia. The latter reaction, which can occur spontaneously, can also be catalysed by EC 3.5.99.10, 2-iminobutanoate/2-iminopropanoate deaminase. The enzyme is involved in L-methionine catabolism.
Links to other databases: BRENDA, EAWAG-BBD, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 42616-25-1
References:
1. Kreis, W. and Hession, C. Isolation and purification of L-methionine-α-deamino-γ-mercaptomethane-lyase (L-methioninase) from Clostridium sporogenes. Cancer Res. 33 (1973) 1862-1865. [PMID: 4720797]