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.
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.
D-Serine, synthesized in neurons 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 (NR1) of the NMDA-type glutamate receptor (NMDAR). For the receptor to open, glutamate and either glycine or D-serine must bind to it; in addition a pore blocker must not be bound (e.g. Mg2+ or Zn2+).[13] In fact, D-serine is a more potent agonist at the glycine site on the NMDAR than glycine itself.
L-Serine is sweet with minor umami and sour tastes at high concentration.