L-isoleucine biosynthesis KEGG:map01110 KEGG:map00660 KEGG:map01100 KEGG:map00260 KEGG:map00280 GO:0009097 PMID:9864346 KEGG:map00290 (2R*,3R*)-2-amino-3-methylpentanoic acid biosynthesis Biosynthesis of L-isoleucine, (2R*,3R*)-2-amino-3-methylpentanoic acid, an hydrophobic branched- chain amino-acid. In most microorganisms, isoleucine is synthesized from aspartate via threonine [Umbarger, H. E. 1978. Amino-acid biosynthesis and its regulation. Annu. Rev. Biochem. 47:533-606]. However, alternative routes to isoleucine from precursors other than threonine have been reported. Some anaerobes can assimilate 2-methylbutyrate into isoleucine. The most commonly observed alternative route was a route from pyruvate and acetyl coenzyme A (acetyl-CoA) via citramalate. This 'pyruvate pathway' was initially proposed for the genus Leptospira because isotope-labeling experiments indicated that in some leptospiral strains, {alpha}-ketobutyrate was derived from pyruvate rather than threonine. Only a limited number of leptospires possess catabolic threonine dehydratase. Later, a similar observation was made with a thermophilic archaeon, Methanobacterium thermoautotrophicum, suggesting that isoleucine biosynthesis involves pyruvate as a precursor. Recently, (R)-citramalate synthase (EC 4.1.3.-) activity was demonstrated in the thermophilic archaeon Methanococcus jannaschii. PMID:15292141 pathway UPa:UPA00047 KEGG:map00966 amino-acid biosynthesis proteinogenic amino-acid biosynthesis