The enzyme threonine synthase (EC 4.2.3.1) catalyzes the chemical reaction
This enzyme belongs to the family of lyases, specifically those carbon-oxygen lyases acting on phosphates. The systematic name of this enzyme class is O-phospho-<small>L</small>-homoserine phosphate-lyase (adding water <small>L</small>-threonine-forming). Other names in common use include threonine synthetase, and O-phospho-<small>L</small>-homoserine phospho-lyase (adding water). This enzyme participates in glycine, serine and threonine metabolism, and vitamin B<sub>6</sub> metabolism. It employs one cofactor, pyridoxal phosphate.
As of late 2007, 7 structures have been solved for this class of enzymes, with PDB accession codes , , , , , , and .