Alternate pathway for isoleucine biosynthesis in Escherichia coli.
A threonine dehydrataseless mutant of Escherichia coli, Crookes strain, was observed to grow on an acetate minimal medium without the usual requirement for isoleucine supplementation. Both the wild-type Crookes strain and a threonine auxotroph metabolized l-glutamate-1-(14)C to l-isoleucine-1-(14)C with no appreciable randomization, suggesting that a pathway for isoleucine formation from glutamate via beta-methylaspartate, beta-methyloxaloacetate, and alpha-ketobutyrate was possible in addition to the pathway from threonine and alpha-ketobutyrate. Crude cell-free extracts formed (14)C-beta-methylaspartate from (14)C-glutamate, and the conversion of beta-methylaspartate to alpha-ketobutyrate was also demonstrated, thus supporting the conclusion that glutamate can serve as a precursor of alpha-ketobutyrate (and isoleucine) without the necessary involvement of threonine as an intermediate.
D000085:Acetates / Q000378:metabolism; D001224:Aspartic Acid / Q000096:biosynthesis / Q000378:metabolism; D002087:Butyrates / Q000096:biosynthesis; D002247:Carbon Isotopes; D002474:Cell-Free System; D002854:Chromatography, Paper; D002855:Chromatography, Thin Layer; D003470:Culture Media; D004586:Electrophoresis; D004590:Electrophoresis, Paper; D004926:Escherichia coli / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D005827:Genetics, Microbial; D005971:Glutamates / Q000378:metabolism; D006836:Hydro-Lyases / Q000378:metabolism; D007532:Isoleucine / Q000096:biosynthesis*; D007535:Isomerases / Q000378:metabolism; D009154:Mutation; D013053:Spectrophotometry; D013912:Threonine / Q000378:metabolism; D000637:Transaminases / Q000378:metabolism
D000085:Acetates; D002087:Butyrates; D002247:Carbon Isotopes; D003470:Culture Media; D005971:Glutamates; D007532:Isoleucine; D013912:Threonine; D001224:Aspartic Acid; D000637:Transaminases; D006836:Hydro-Lyases; D007535:Isomerases