L-methionine biosynthesis via de novo pathway PMID:12951250 PMID:10469143 UPa:UPA00051 pathway KEGG:map00920 PMID:12948640 PMID:15215334 KEGG:map00300 KEGG:map01120 Sulfur-containing amino-acid L-methionine (2-amino-4-(methylthio)butanoic acid) is synthesized de novo by most microorganisms and plants after the initial steps of inorganic sulfate assimilation and synthesis of cysteine or homocysteine. There are two alternative pathways of methionine synthesis in microorganisms. The enterobacterial type trans-sulfuration pathway involves cystathionine as an intermediate and utilizes cysteine as the sulfur source. In contrast, the direct sulfhydrylation pathway found in yeast (Saccharomyces cerevisiae), spirochete (Leptospira meyeri) and actinomycetes (Corynebacterium glutamicum) bypasses cystathionine and uses inorganic sulfur instead. Although yeast, fungi and higher plants have both transsulfuration and direct sulfhydrylation pathways, only the bacteria C. glutamicum, B. subtilis, P. aeruginosa, P. putida and L. meyeri have been shown to have both pathways. Methionine biosynthesis is a central pathway, as it controls a large number of cellular processes such as translation of mRNA into proteins (not only as a substrate for protein elongation but also as the initiator of protein synthesis) and transmethylation reactions via the formation of S-adenosylmethionine (SAM) (cf activated methyl cycle pathway). KEGG:map01100 KEGG:map01110 KEGG:map00670 KEGG:map00260 2-amino-4-(methylthio)butanoic acid biosynthesis KEGG:map00270 PMID:12845493 amino-acid biosynthesis L-methionine biosynthesis