If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: methionine biosynthesis from homoserine, methionine biosynthesis by transsulfuration
|Superclasses:||Biosynthesis → Amino Acids Biosynthesis → Proteinogenic Amino Acids Biosynthesis → L-methionine Biosynthesis → L-methionine De Novo Biosynthesis|
Pathway Summary from MetaCyc:
L-methionine (met) is an essential amino acid and is required for a number of important cellular functions, including the initiation of protein synthesis, the methylation of DNA, rRNA and xenobiotics, and the biosynthesis of cysteine, phospholipids and polyamines.
Some bacteria can synthesize methionine using organic sulfur through transsulfuration of O-acylated homoserine with L-cysteine to form L-cystathionine. Cystathionine is then cleaved to L-homocysteine, which is methylated to methionine (this pathway) [Soda87].
Some bacteria, yeast and fungi can use a different route in which they directly assimilate inorganic sulfur by a sulfhydrylation (see L-methionine biosynthesis III). In that route hydrogen sulfide (H2S), the final product of microbial sulfate reduction (see MetaCyc pathway sulfate reduction I (assimilatory)) reacts with O-acylated homoserine, with replacement of the acetyl group by sulfide to form homocysteine (see L-homocysteine biosynthesis).
L-homocysteine is methylated to L-methionine via either a cobalamin-independent enzyme (EC 18.104.22.168) or a cobalamin-dependent enzyme (EC 22.214.171.124), depending upon the species or growth conditions [Thomas97, Ruckert03].
The O-acyl group of homoserine is an acetyl group in fungi, yeast, and most Gram-positive bacteria (see L-methionine biosynthesis III) and a succinyl group in enteric bacteria and some other Gram-negative bacteria, such as Pseudomanas aeruginosa, and Pseudomonas putida (this pathway) ([Vermeij99, Soda87, 1]).
While many organisms seem to contain both routes for methionine biosynthesis, in Escherichia coli and other enteric bacteria only the transsulfuration pathway is used (Greene, R.C. in [Neidhardt87] pp. 542-560). Published evidence for these pathways includes gene identification; complementation of known mutants; analysis of mutant phenotypes; and gene cloning, expression, and enzyme activity assays. The presence of EC 126.96.36.199, O-acetylhomoserine aminocarboxypropyltransferase was considered indicative of the presence of a direct sulfhydrylation pathway.
Cynthia J. Krieger on Wed Oct 15, 2003:
This pathway was formerly called methionine biosynthesis from homoserine.
Pathway Evidence Glyph:
Key to pathway glyph edge colors:
An enzyme catalyzing this reaction is present in this organism
No enzyme catalyzing this reaction has been identified in this organism
The reaction and any enzyme that catalyzes it (if one has been identified) is unique to this pathway
Revised 07-May-2007 by SRI International
Neidhardt87: Neidhardt FC, Ingraham J, Low KB, Magasanik B, Schaechter M, Umbarger HE "Escherichia coli and Salmonella typhimurium, Cellular and Molecular Biology, Volumes 1 & 2." Microbiology, Washington, D.C., 1987.
Ruckert03: Ruckert C, Puhler A, Kalinowski J (2003). "Genome-wide analysis of the L-methionine biosynthetic pathway in Corynebacterium glutamicum by targeted gene deletion and homologous complementation." J Biotechnol 104(1-3);213-28. PMID: 12948640
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