Homoserine

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 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]

l-Homoserine

Skeletal formula
Ball-and-stick model of the zwitterion
Names
IUPAC name (S)-2-Amino-4-hydroxybutanoic acid
Identifiers
CAS Number	672-15-1 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30653 Y
ChEMBL	ChEMBL11722 N
ChemSpider	758 Y
ECHA InfoCard	100.010.538
EC Number	211-590-6
PubChem CID	779
UNII	6KA95X0IVO Y
CompTox Dashboard (EPA)	DTXSID5075159
InChI InChI=1S/C4H9NO3/c5-3(1-2-6)4(7)8/h3,6H,1-2,5H2,(H,7,8) Y Key: UKAUYVFTDYCKQA-UHFFFAOYSA-N Y 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). N verify (what is YN ?) Infobox references

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.^{[clarification needed]} 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]

Biosynthesis pathway for homoserine.

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]