|CAS number||(L-isomer) , , (D-isomer)|
|Jmol-3D images||Image 1|
|Molar mass||105.09 g mol−1|
|Appearance||white crystals or powder|
|Density||1.603 g/cm3 (22 °C)|
|Melting point||246 °C (475 °F; 519 K) decomposes|
|Solubility in water||soluble|
|Acidity (pKa)||2.21 (carboxyl), 9.15 (amino)|
|Supplementary data page|
|n, εr, etc.|
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Serine (abbreviated as Ser or S) is an amino acid with the formula HO2CCH(NH2)CH2OH. It is one of the proteinogenic amino acids. Its codons in the genetic code are UCU, UCC, UCA, UCG, AGU and AGC. By virtue of the hydroxyl group, serine is classified as a polar amino acid.
Occurrence and biosynthesis
This compound is one of the naturally occurring proteinogenic amino acids. Only the L-stereoisomer appears naturally in proteins. It is not essential to the human diet, since it is synthesized in the body from other metabolites, including glycine. Serine was first obtained from silk protein, a particularly rich source, in 1865. Its name is derived from the Latin for silk, sericum. Serine's structure was established in 1902.
The biosynthesis of serine starts with the oxidation of 3-phosphoglycerate to 3-phosphohydroxypyruvate and NADH. Reductive amination of this ketone followed by hydrolysis gives serine. Serine hydroxymethyltransferase catalyzes the reversible, simultaneous conversions of L-serine to glycine (retro-aldol cleavage) and 5,6,7,8-tetrahydrofolate to 5,10-methylenetetrahydrofolate (hydrolysis).
This compound may also be naturally produced when UV light illuminates simple ices such as a combination of water, methanol, hydrogen cyanide, and ammonia, suggesting that it may be easily produced in cold regions of space.
Industrially, L-serine is produced by fermentation, with an estimated 100-1000 tonnes per year produced. In the laboratory, racemic serine can be prepared from methyl acrylate via several steps:
Serine is important in metabolism in that it participates in the biosynthesis of purines and pyrimidines. It is the precursor to several amino acids including glycine and cysteine, and tryptophan in bacteria. It is also the precursor to numerous other metabolites, including sphingolipids and folate, which is the principal donor of one-carbon fragments in biosynthesis.
Serine plays an important role in the catalytic function of many enzymes. It has been shown to occur in the active sites of chymotrypsin, trypsin, and many other enzymes. The so-called nerve gases and many substances used in insecticides have been shown to act by combining with a residue of serine in the active site of acetylcholine esterase, inhibiting the enzyme completely.
Serine proteases are a common type of protease.
D-Serine, synthesized in the brain by serine racemase from L-serine (its enantiomer), serves as a neuromodulator by coactivating NMDA receptors, making them able to open if they then also bind glutamate. D-serine is a potent agonist at the glycine site of the NMDA-type glutamate receptor. For the receptor to open, glutamate and either glycine or D-serine must bind to it. In fact, D-serine is a more potent agonist at the glycine site on the NMDAR than glycine itself. D-serine was only thought to exist in bacteria until relatively recently; it was the second D amino acid discovered to naturally exist in humans, present as a signalling molecule in the brain, soon after the discovery of D-aspartate. Had D amino acids been discovered in humans sooner, the glycine site on the NMDA receptor might instead be named the D-serine site.
Pure D-serine is an off-white crystalline powder with a very faint musty aroma. L-Serine is sweet with minor umami and sour tastes at high concentration. D-Serine is sweet with an additional minor sour taste at medium and high concentrations.
Research for therapeutic use
D-Serine is being studied in rodents as a potential treatment for schizophrenia and L-serine is in FDA-approved human clinical trials as a possible treatment for ALS. A 2011 meta-analysis found adjunctive sarcosine to have a medium effect size for negative and total symptoms.
- Serine aggregation properties in Serine octamer clusters
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