Serine

Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the L-stereoisomer appears in mammalian protein. It is not essential to the human diet, since it can be 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 hydroxyl group attached makes it a polar amino acid.

Synthesis
The synthesis of serine and glycine starts with the oxidation of 3-phosphoglycerate forming 3-phosphohydroxypyruvate and NADH. A transamination reaction with glutamic acid forms 3-phosphoserine and removal of Pi yields serine.

Function
Serine is important in metabolism in that it participates in the biosynthesis of purines and pyrimidines, cysteine, tryptophan (in bacteria), and a large number of other metabolites.

When incorporated into the structure of enzymes, serine often plays an important role in their catalytic function. 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. Without the esterase activity that usually destroys acetylcholine as soon as it performs its function, dangerously high levels of this neurotransmitter build up, quickly resulting in convulsions and death.

As a constituent (residue) of proteins, its side chain can undergo O-linked glycosylation. This might be important in explaining some of the devastating consequences of diabetes. It is one of three amino acid residues that are commonly phosphorylated by kinases during cell signalling in eukaryotes. Phosphorylated serine residues are often referred to as phosphoserine. Serine proteases are a common type of protease.

D-serine, synthesized by serine racemase from L-serine, acts as a neuronal signaling molecule by activating NMDA receptors in the brain.

Serine is also a precursor to Folate which is the principle donator of one carbon fragments for biosynthesis.