-!- The enzyme cleaves a carbon-oxygen bond, releasing a water molecule (hence the enzyme's original classification as EC 4.2.1.14) and an unstable enamine product that tautomerizes to an imine form, which undergoes a hydrolytic deamination to form pyruvate and ammonia. -!- The latter reaction, which can occur spontaneously, can also be catalyzed by EC 3.5.99.10. -!- Also acts, slowly, on D-threonine. -!- Formerly EC 4.2.1.14.

-!- Highly selective for L-serine as substrate. -!- D-serine is found in type-II astrocytes in mammalian brain, where it appears to be an endogenous ligand of the glycine site of N-methyl-D- aspartate (NMDA) receptors. -!- The reaction can also occur in the reverse direction but does so more slowly at physiological serine concentrations.

-!- The reaction catalyzed by both types of enzymes involves the initial elimination of water to form an enamine intermediate (hence the enzyme's original classification as EC 4.2.1.13) followed by tautomerization to an imine form and hydrolysis of the C-N bond. -!- The latter reaction, which can occur spontaneously, is also be catalyzed by EC 3.5.99.10. -!- This reaction is also carried out by EC 4.3.1.19 from a number of sources. -!- Formerly EC 4.2.1.13.