The enzyme threonine aldolase (EC 4.1.2.5) is an enzyme not found in humans that catalyzes the chemical reaction
L-threonine ⇌ {\displaystyle \rightleftharpoons } glycine + acetaldehyde This enzyme belongs to the family of lyases, specifically the aldehyde-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is L-threonine acetaldehyde-lyase (glycine-forming). This enzyme is also called L-threonine acetaldehyde-lyase. This enzyme participates in glycine, serine and threonine metabolism. It employs one cofactor, pyridoxal phosphate.
Structural studies As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes PDB: 1JG8, PDB: 1LW4, PDB: 1LW5, PDB: 1M6S, and PDB: 1SVV.
Presence in human and mouse
Some early evidence from 2005 suggests that the mouse ortholog enzyme, Tha1 (or GLY1), is synthesized and functional in mice, but this has not been reviewed by certain major groups like UniProt (as of August 2026). Humans also have the remnants of the gene denoted THA1P (or GLY1), however it seems to be damaged by past mutations and inactive. RNA expression has not been found in major databases, suggesting that it isn't transcribed. Moreover, the pseudogene contains two single nucleotide deletions which would cause frameshifts even if were to be transcribed.
References
Bell SC; Turner JM (1973). "Bacterial threonine aldolase and serine hydroxymethyltransferase enzyme". Biochem. Soc. Trans. 1 (3): 678–681. doi:10.1042/bst0010678. KARASEK MA, GREENBERG DM (1957). "Studies on the properties of threonine aldolases". J. Biol. Chem. 227 (1): 191–205. doi:10.1016/S0021-9258(18)70806-5. PMID 13449064. Kumagai H, Nagate T, Yoshida H, Yamada H (1972). "Threonine aldolase from Candida humicola. II. Purification, crystallization and properties". Biochim. Biophys. Acta. 258 (3): 779–90. doi:10.1016/0005-2744(72)90179-9. PMID 5017702.