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: D-threonine aldolase
Reaction: (1) D-threonine = glycine + acetaldehyde
(2) D-allothreonine = glycine + acetaldehyde
Glossary: D-threonine = (2R,3S)-2-amino-3-hydroxybutanoic acid
D-allothreonine = (2R,3R)-2-amino-3-hydroxybutanoic acid
Other name(s): D-TA; DTA; low specificity D-TA; low specificity D-threonine aldolase
Systematic name: D-threonine acetaldehyde-lyase (glycine-forming)
Comments: A pyridoxal-phosphate protein that is activated by divalent metal cations (e.g. Co2+, Ni2+, Mn2+ or Mg2+) [1,2]. The reaction is reversible, which can lead to the interconversion of D-threonine and D-allothreonine [1]. Several other D-β-hydroxy-α-amino acids, such as D-β-phenylserine, D-β-hydroxy-α-aminovaleric acid and D-β-3,4-dihydroxyphenylserine, can also act as substrate [1].
1.  Kataoka, M., Ikemi, M., Morikawa, T., Miyoshi, T., Nishi, K., Wada, M., Yamada, H. and Shimizu, S. Isolation and characterization of D-threonine aldolase, a pyridoxal-5′-phosphate-dependent enzyme from Arthrobacter sp. DK-38. Eur. J. Biochem. 248 (1997) 385–393. [PMID: 9346293]
2.  Liu, J.Q., Dairi, T., Itoh, N., Kataoka, M., Shimizu, S. and Yamada, H. A novel metal-activated pyridoxal enzyme with a unique primary structure, low specificity D-threonine aldolase from Arthrobacter sp. Strain DK-38. Molecular cloning and cofactor characterization. J. Biol. Chem. 273 (1998) 16678–16685. [PMID: 9642221]
3.  Liu, J.Q., Odani, M., Dairi, T., Itoh, N., Shimizu, S. and Yamada, H. A new route to L-threo-3-[4-(methylthio)phenylserine], a key intermediate for the synthesis of antibiotics: recombinant low-specificity D-threonine aldolase-catalyzed stereospecific resolution. Appl. Microbiol. Biotechnol. 51 (1999) 586–591. [PMID: 10390816]
4.  Liu, J.Q., Odani, M., Yasuoka, T., Dairi, T., Itoh, N., Kataoka, M., Shimizu, S. and Yamada, H. Gene cloning and overproduction of low-specificity D-threonine aldolase from Alcaligenes xylosoxidans and its application for production of a key intermediate for parkinsonism drug. Appl. Microbiol. Biotechnol. 54 (2000) 44–51. [PMID: 10952004]
5.  Liu, J.Q., Dairi, T., Itoh, N., Kataoka, M., Shimizu, S. and Yamada, H. Diversity of microbial threonine aldolases and their application. J. Mol. Catal. B 10 (2000) 107–115.
6.  Paiardini, A., Contestabile, R., D'Aguanno, S., Pascarella, S. and Bossa, F. Threonine aldolase and alanine racemase: novel examples of convergent evolution in the superfamily of vitamin B6-dependent enzymes. Biochim. Biophys. Acta 1647 (2003) 214–219. [PMID: 12686135]
[EC created 2007]
Accepted name: 3-hydroxy-D-aspartate aldolase
Reaction: (1) threo-3-hydroxy-D-aspartate = glycine + glyoxylate
(2) D-erythro-3-hydroxyaspartate = glycine + glyoxylate
Other name(s): D-3-hydroxyaspartate aldolase
Systematic name: 3-hydroxy-D-aspartate glyoxylate-lyase (glycine-forming)
Comments: A pyridoxal-phosphate protein. The enzyme, purified from the bacterium Paracoccus denitrificans IFO 13301, is strictly D-specific as to the α-position of the substrate, but accepts both the threo and erythro forms at the β-position. The erythro form is a far better substrate (about 100-fold). The enzyme can also accept D-allothreonine, D-threonine, erythro-3-phenyl-D-serine and threo-3-phenyl-D-serine. Different from EC, erythro-3-hydroxy-L-aspartate aldolase. Requires a divalent cation, such as Mg2+, Mn2+ or Co2+.
1.  Liu, J.Q., Dairi, T., Itoh, N., Kataoka, M. and Shimizu, S. A novel enzyme, D-3-hydroxyaspartate aldolase from Paracoccus denitrificans IFO 13301: purification, characterization, and gene cloning. Appl. Microbiol. Biotechnol. 62 (2003) 53–60. [PMID: 12835921]
[EC created 2011]
Accepted name: D-serine ammonia-lyase
Reaction: D-serine = pyruvate + NH3 (overall reaction)
(1a) D-serine = 2-aminoprop-2-enoate + H2O
(1b) 2-aminoprop-2-enoate = 2-iminopropanoate (spontaneous)
(1c) 2-iminopropanoate + H2O = pyruvate + NH3 (spontaneous)
Other name(s): D-hydroxyaminoacid dehydratase; D-serine dehydrase; D-hydroxy amino acid dehydratase; D-serine hydrolase; D-serine dehydratase (deaminating); D-serine deaminase; D-serine hydro-lyase (deaminating)
Systematic name: D-serine ammonia-lyase (pyruvate-forming)
Comments: A pyridoxal-phosphate protein. The enzyme cleaves a carbon-oxygen bond, releasing a water molecule (hence the enzyme’s original classification as EC, D-serine dehydratase) 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 catalysed by EC, 2-iminobutanoate/2-iminopropanoate deaminase. Also acts, slowly, on D-threonine.
1.  Dupourque, D., Newton, W.A. and Snell, E.E. Purification and properties of D-serine dehydrase from Escherichia coli. J. Biol. Chem. 241 (1966) 1233–1238. [PMID: 5327100]
2.  Metzler, D.E. and Snell, E.E. Deamination of serine. II. D-Serine dehydrase, a vitamin B6 enzyme from Escherichia coli. J. Biol. Chem. 198 (1952) 363–373. [PMID: 12999751]
[EC created 1961 as EC, transferred 2001 to EC]
Accepted name: threonine racemase
Reaction: L-threonine = D-threonine
Glossary: D-threonine = (2R,3S)-2-amino-3-hydroxybutanoic acid
Systematic name: threonine racemase
Comments: Inverts both chiral centres.
1.  Amos, H. A racemase for threonine in Escherichia coli. J. Am. Chem. Soc. 76 (1954) 3858.
[EC created 1961, modified 1981]

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