Homoserine

l-Homoserine
Names
	IUPAC name (S)-2-Amino-4-hydroxybutanoic acid
Identifiers
CAS Number	672-15-1 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:30653 ;
ChEMBL	ChEMBL11722 ;
ChemSpider	758 ;
ECHA InfoCard	100.010.538
EC Number	211-590-6;
PubChem CID	779;
UNII	6KA95X0IVO ;
CompTox Dashboard (EPA)	DTXSID5075159 ;
	InChI InChI=1S/C4H9NO3/c5-3(1-2-6)4(7)8/h3,6H,1-2,5H2,(H,7,8) Key: UKAUYVFTDYCKQA-UHFFFAOYSA-N ; InChI=1/C4H9NO3/c5-3(1-2-6)4(7)8/h3,6H,1-2,5H2,(H,7,8) Key: UKAUYVFTDYCKQA-UHFFFAOYAZ;
	SMILES O=C(O)C(N)CCO;
Properties
Chemical formula	C4H9NO3
Molar mass	119.12 g/mol
Melting point	203 °C (decomposes)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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 -CH₂- unit into the backbone. Homoserine, or its lactone form, 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] Its complete biosynthetic pathway includes glycolysis, the tricarboxylic acid (TCA) or citric acid cycle (Krebs cycle), and the aspartate metabolic pathway. It forms by two reductions of aspartic acid via the intermediacy of aspartate semialdehyde.^[2] Specifically, the enzyme homoserine dehydrogenase, in association with NADPH, catalyzes a reversible reaction that interconverts L-aspartate-4-semialdehyde to L-homoserine. Then, two other enzymes, homoserine kinase and homoserine O-succinyltransferase use homoserine as a substrate and produce phosphohomoserine and O-succinyl homoserine respectively.^[3]

Applications

Commercially, homoserine can serve as precursor to the synthesis of isobutanol and 1,4-butanediol.^[4] Purified homoserine is used in enzyme structural studies.^[5] Also, homoserine has played important roles in studies to elucidate peptide synthesis and synthesis of proteoglycan glycopeptides.^[6] Bacterial cell lines can make copious amounts of this amino acid.^[3]^[4]

Biosynthesis

Homoserine is produced from aspartate via aspartate-4-semialdehyde, which is produced from β-phosphoaspartate. By the action of homoserine dehydrogenases, the semialdehyde is converted to homoserine.^[7]

L-Homoserine is substrate for homoserine kinase, yielding phosphohomoserine (homoserine-phosphate), which is converted to by threonine synthase to yield L-threonine.

Homoserine is converted to O-succinyl homoserine by homoserine O-succinyltransferase, a precursor to L-methionine.^[8]

Homoserine allosterically inhibits aspartate kinase and glutamate dehydrogenase.^[3] 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]