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Last Updated: 2018-12-21
Isoleucine biosynthesis begins with L-threonine from the threonine biosynthesis pathway. L-threonine interacts with a threonine dehydratase biosynthetic releasing water, a hydrogen ion and (2Z)-2-aminobut-2-enoate. This compound is isomerized into a 2-iminobutanoate which interacts with water and a hydrogen ion spontaneously, resulting in the release of ammonium and 2-ketobutyric acid. This compound reacts with pyruvic acid and hydrogen ion through an acetohydroxybutanoate synthase / acetolactate synthase 2 resulting in carbon dioxide and (S)-2-Aceto-2-hydroxybutanoic acid. The latter compound is reduced by an NADPH driven acetohydroxy acid isomeroreductase releasing NADP and acetohydroxy acid isomeroreductase. The latter compound is dehydrated by a dihydroxy acid dehydratase resulting in 3-methyl-2-oxovaleric acid.This compound reacts in a reversible reaction with L-glutamic acid through a Branched-chain-amino-acid aminotransferase resulting in oxoglutaric acid and L-isoleucine. L-isoleucine can also be transported into the cytoplasm through two different methods: a branched chain amino acid ABC transporter or a branched chain amino acid transporter BrnQ y.
Isoleucine Biosynthesis References
Bell SC, Turner JM, Collins J, Gray TR: Patterns of microbial threonine catabolism: a survey. Biochem J. 1972 Apr;127(3):77P.Pubmed: 5076220
Bell SC, Turner JM: Bacterial catabolism of threonine. Threonine degradation initiated by l-threonine hydrolyase (deaminating) in a species of Corynebacterium. Biochem J. 1977 Jun 15;164(3):579-87.Pubmed: 16743051
Calhoun DH, Rimerman RA, Hatfield GW: Threonine deaminase from Escherichia coli. I. Purification and properties. J Biol Chem. 1973 May 25;248(10):3511-6.Pubmed: 4573981
Gollop N, Damri B, Barak Z, Chipman DM: Kinetics and mechanism of acetohydroxy acid synthase isozyme III from Escherichia coli. Biochemistry. 1989 Jul 25;28(15):6310-7.Pubmed: 2675968
Grimminger H, Umbarger HE: Acetohydroxy acid synthase I of Escherichia coli: purification and properties. J Bacteriol. 1979 Feb;137(2):846-53.Pubmed: 370104
Komatsubara S, Murata K, Kisumi M, Chibata I: Threonine degradation by Serratia marcescens. J Bacteriol. 1978 Aug;135(2):318-23.Pubmed: 355220
Lee-Peng FC, Hermodson MA, Kohlhaw GB: Transaminase B from Escherichia coli: quaternary structure, amino-terminal sequence, substrate specificity, and absence of a separate valine-alpha-ketoglutarate activity. J Bacteriol. 1979 Aug;139(2):339-45.Pubmed: 378964
MYERS JW: Dihydroxy acid dehydrase: an enzyme involved in the biosynthesis of isoleucine and valine. J Biol Chem. 1961 May;236:1414-8.Pubmed: 13727223
Ratzkin B, Arfin S, Umbarger HE: Isoleucine and valine metabolism in Escherichia coli. 18. Induction of acetohydroxy acid isomeroreductase. J Bacteriol. 1972 Oct;112(1):131-41.Pubmed: 4562389
UMBARGER HE, BROWN B: Threonine deamination in Escherichia coli. II. Evidence for two L-threonine deaminases. J Bacteriol. 1957 Jan;73(1):105-12.Pubmed: 13405870
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