If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Degradation/Utilization/Assimilation → Amino Acids Degradation → Proteinogenic Amino Acids Degradation → L-methionine Degradation|
Pathway Summary from MetaCyc:
In the degradation pathway shown here, L-methionine is first metabolized toS-adenosyl-L-methionine (SAM), a compound that mediates most biological methylations. In the second reaction, the S-methyl group is transferred to other acceptors in a transmethylation step. The product, S-adenosyl-L-homocysteine, is then hydrolyzed to L-homocysteine and adenosine.
L-homocysteine is a branch point. In rats and humans approximately half of the homocysteine formed is remethylated back to methionine via two salvage pathways, one involving methionine synthase (EC 220.127.116.11), and the other involving betaine-homocysteine S-methyltransferase (EC 18.104.22.168) (see L-methionine salvage from L-homocysteine).
The remainder of the homocysteine is degraded further. The first step is the condensation with serine to form L-cystathionine. cystathionine γ-lyase catalyzes cleavage of the C-γ-S bond of L-cystathionine, yielding L-cysteine, 2-oxobutanoate and ammonia in a transsulfuration reaction (see L-cysteine biosynthesis III (from L-homocysteine)) [Griffith87, Finkelstein90].
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
Created in MetaCyc 15-Mar-1999 by Wagg J , SRI International
Revised in MetaCyc 13-Sep-2006 by Caspi R , SRI International
Imported from MetaCyc 08-Aug-2014 by Subhraveti P , SRI International
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