Serine

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General Features
Molecular Formula: C₃H₇NO₃ or HO₂CCH(NH₂)CH₂OH
Molecular Mass: 105.09 g/mol
Abbreviation: Ser or S
pKa= 2.21 (carboxyl), 9.15 (amino)

The hydroxyl group classifies serine as a polar amino acid. Serine is not an essential amino acid and can be synthesized.  Serine was first isolated from silk protein in 1865.  Its name comes from the Latin for silk, sericum.

Physiological Roles
Serine is a naturally occurring proteinogenic amino acid (precursor to proteins).  Only the L-stereoisomer appears in proteins.  Its codons are UCU, UCC, UCA, UCG, AGU, and AGC.

Serine is also important in metabolism.  It is involved in the synthesis of purine and pyrimidines.  For more information of nucleotide synthesis, please visit Nucleotide Metabolism: Nucleic Acid Synthesis.  Serine is also the precursor for glycine and cysteine.  It is also important in the synthesis of tryptophan in bacteria. Serine is also the precursor of sphingolipids, folate, and many other metabolities. For more information on folate synthesis, please read "Folate Synthesis by Intestinal Bacteria" by Dr. Frederick Klipstein and Dr. I. Michael Samloff.


Serine also plays a role in proteolysis.  Serine proteases are enzymes with a serine residue attached at the active site.  Serine proteases are believed to make up one-third of known proteolytic enzymes in eukaryotes.  The number of proteolytic enzymes in prokaryotes is not known.  Their function in bacteria include adaptation of the external environment, cell signaling, development, pathogenesis, and many other functions. Serine proteases contribute to antibiotic resistance; serine beta-lactamases open the ring structure of beta-lactam antibiotics.  For more information on the roles of serine proteases, please read "Genome-wide survey of prokaryotic serine proteases: analysis of distribution and domain architectures of five serine protease families in prokaryotes."


Synthesis


Synthesis of serine starts with oxidation of 3-phosphoglycerate.  This forms 3-phosphohydroxy pyruvate and NADH.  A transamination reaction with glutamate forms 3-phosphoserine.  The removal of the phosphate yields serine.

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