Homoserine
Template:Chembox Homoserine (also called isothreonine) is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2OH. L-Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an additional [[methylene bridge|Template:Chem2 unit]] into the sidechain. Homoserine, or its lactone, is the product of a cyanogen bromide cleavage of a peptide by degradation of methionine. Homoserine is an intermediate in the biosynthesis of three essential amino acids: methionine, threonine (an isomer of homoserine), and isoleucine.[1]
Applications
Commercially, homoserine can serve as precursor to the synthesis of isobutanol and 1,4-butanediol.[2] Purified homoserine is used in enzyme structural studies.[3] Also, homoserine has played important roles in studies to elucidate peptide synthesis and synthesis of proteoglycan glycopeptides.[4] Bacterial cell lines can make copious amounts of this amino acid.[5][2]
Biosynthesis
Its complete biosynthetic pathway includes glycolysis, the tricarboxylic acid (TCA) or citric acid cycle (Krebs cycle), and the aspartate metabolic pathway.Script error: No such module "Unsubst". It forms by two reductions of aspartic acid via the intermediacy of aspartate semialdehyde.[6] Specifically, the enzyme homoserine dehydrogenase, in association with NADPH, catalyzes a reversible reaction that interconverts L-aspartate-4-semialdehyde to L-homoserine. Homoserine kinase and homoserine O-succinyltransferase convert homoserine to phosphohomoserine and O-succinyl homoserine, respectively.[5] Homoserine is produced from aspartate via the intermediate aspartate-4-semialdehyde, which is produced from β-phosphoaspartate. By the action of homoserine dehydrogenases, the semialdehyde is converted to homoserine.[7]
Other biochemical roles
L-Homoserine is substrate for homoserine kinase, yielding phosphohomoserine (homoserine-phosphate), which is converted by threonine synthase to L-threonine.
Homoserine is converted to O-succinyl homoserine by homoserine O-succinyltransferase. O-succinyl homoserine is a precursor to L-methionine.[8]
Homoserine inhibits aspartate kinase and glutamate dehydrogenase.[5] Glutamate dehydrogenase reversibly converts glutamate to α-ketoglutarate and α-ketoglutarate coverts to oxaloacetate through the citric cycle. Threonine acts as another allosteric inhibitor of aspartate kinase and homoserine dehydrogenase, but it is a competitive inhibitor of homoserine kinase.[8]
References
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- ↑ Berg, J. M.; Stryer, L. et al. (2002), Biochemistry. W.H. Freeman. Template:ISBN
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- ↑ a b Script error: No such module "Citation/CS1".
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