Accepted name: 3-hydroxy acid dehydrogenase
Reaction: L-allo-threonine + NADP+ = aminoacetone + CO2 + NADPH + H+ (overall reaction)
(1a) L-allo-threonine + NADP+ = L-2-amino-3-oxobutanoate + NADPH + H+
(1b) L-2-amino-3-oxobutanoate = aminoacetone + CO2 (spontaneous)
Glossary: L-allo-threonine = (2S,3S)-2-amino-3-hydroxybutanoic acid
aminoacetone = 1-aminopropan-2-one
L-2-amino-3-oxobutanoate = (2S)-2-amino-3-oxobutanoate
Other name(s): ydfG (gene name); YMR226c (gene name)
Systematic name: L-allo-threonine:NADP+ 3-oxidoreductase
Comments: The enzyme, purified from the bacterium Escherichia coli and the yeast Saccharomyces cerevisiae, shows activity with a range of 3- and 4-carbon 3-hydroxy acids. The highest activity is seen with L-allo-threonine and D-threonine. The enzyme from Escherichia coli also shows high activity with L-serine, D-serine, (S)-3-hydroxy-2-methylpropanoate and (R)-3-hydroxy-2-methylpropanoate. The enzyme has no activity with NAD+ or L-threonine (cf. EC, L-threonine 3-dehydrogenase).
1.  Fujisawa, H., Nagata, S. and Misono, H. Characterization of short-chain dehydrogenase/reductase homologues of Escherichia coli (YdfG) and Saccharomyces cerevisiae (YMR226C). Biochim. Biophys. Acta 1645 (2003) 89–94. [PMID: 12535615]
[EC created 2014, modified 2015]
Accepted name: L-threonine aldolase
Reaction: L-threonine = glycine + acetaldehyde
Other name(s): L-threonine acetaldehyde-lyase
Systematic name: L-threonine acetaldehyde-lyase (glycine-forming)
Comments: A pyridoxal-phosphate protein. This enzyme is specific for L-threonine and can not utilize L-allo-threonine. Different from EC, L-allo-threonine aldolase, and EC, low-specificity L-threonine aldolase.
1.  Dainty, R.H. Purification and properties of threonine aldolase from Clostridium pasteurianum. Biochem. J. 117 (1970) 585–592. [PMID: 5419751]
2.  Karasek, M.A. and Greenberg, D.M. Studies on the properties of threonine aldolases. J. Biol. Chem. 227 (1957) 191–205. [PMID: 13449064]
[EC created 1961, deleted 1972, reinstated 1976, modified 2011]
Accepted name: low-specificity L-threonine aldolase
Reaction: (1) L-threonine = glycine + acetaldehyde
(2) L-allo-threonine = glycine + acetaldehyde
Other name(s): LtaE
Systematic name: L-threonine/L-allo-threonine acetaldehyde-lyase (glycine-forming)
Comments: Requires pyridoxal phosphate. The low-specificity L-threonine aldolase can act on both L-threonine and L-allo-threonine [1,2]. The enzyme from Escherichia coli can also act on L-threo-phenylserine and L-erythro-phenylserine [4]. The enzyme can also catalyse the aldol condensation of glycolaldehyde and glycine to form 4-hydroxy-L-threonine, an intermediate of pyridoxal phosphate biosynthesis [3]. Different from EC, L-threonine aldolase, and EC, L-allo-threonine aldolase.
1.  Yamada, H., Kumagai, H., Nagate, T. and Yoshida, H. Crystalline threonine aldolase from Candida humicola. Biochem. Biophys. Res. Commun. 39 (1970) 53–58. [PMID: 5438301]
2.  Kumagai, H., Nagate, T., Yoshida, H. and Yamada, H. Threonine aldolase from Candida humicola. II. Purification, crystallization and properties. Biochim. Biophys. Acta 258 (1972) 779–790. [PMID: 5017702]
3.  Liu, J.Q., Nagata, S., Dairi, T., Misono, H., Shimizu, S. and Yamada, H. The GLY1 gene of Saccharomyces cerevisiae encodes a low-specific L-threonine aldolase that catalyzes cleavage of L-allo-threonine and L-threonine to glycine—expression of the gene in Escherichia coli and purification and characterization of the enzyme. Eur. J. Biochem. 245 (1997) 289–293. [PMID: 9151955]
4.  Liu, J.Q., Dairi, T., Itoh, N., Kataoka, M., Shimizu, S. and Yamada, H. Gene cloning, biochemical characterization and physiological role of a thermostable low-specificity L-threonine aldolase from Escherichia coli. Eur. J. Biochem. 255 (1998) 220–226. [PMID: 9692922]
5.  Kim, J., Kershner, J.P., Novikov, Y., Shoemaker, R.K. and Copley, S.D. Three serendipitous pathways in E. coli can bypass a block in pyridoxal-5′-phosphate synthesis. Mol. Syst. Biol. 6:436 (2010). [PMID: 21119630]
[EC created 2011]
Accepted name: L-allo-threonine aldolase
Reaction: L-allo-threonine = glycine + acetaldehyde
Systematic name: L-allo-threonine acetaldehyde-lyase (glycine-forming)
Comments: Requires pyridoxal phosphate. This enzyme, characterized from the bacterium Aeromonas jandaei, is specific for L-allo-threonine and can not act on either L-threonine or L-serine. Different from EC, L-threonine aldolase, and EC, low-specificity L-threonine aldolase. A previously listed enzyme with this name, EC, was deleted in 1971 after it was found to be identical to EC, glycine hydroxymethyltransferase.
1.  Kataoka, M., Wada, M., Nishi, K., Yamada, H. and Shimizu, S. Purification and characterization of L-allo-threonine aldolase from Aeromonas jandaei DK-39. FEMS Microbiol. Lett. 151 (1997) 245–248. [PMID: 9228760]
[EC created 2011]