ExplorEnz: EC 4.3.1.19

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4.3.1.19

Accepted name:

threonine ammonia-lyase

Reaction:

L-threonine = 2-oxobutanoate + NH₃ (overall reaction)
(1a) L-threonine = 2-aminobut-2-enoate + H₂O
(1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous)
(1c) 2-iminobutanoate + H₂O = 2-oxobutanoate + NH₃ (spontaneous)

For diagram of isoleucine and valine biosynthesis, click here

Other name(s):

threonine deaminase; L-serine dehydratase; serine deaminase; L-threonine dehydratase; threonine dehydrase; L-threonine deaminase; threonine dehydratase; L-threonine hydro-lyase (deaminating); L-threonine ammonia-lyase

Systematic name:

L-threonine ammonia-lyase (2-oxobutanoate-forming)

Comments:

Most enzymes that catalyse this reaction are pyridoxal-phosphate-dependent, although some enzymes contain an iron-sulfur cluster instead. The reaction catalysed by both types of enzymes involves the initial elimination of water to form an enamine intermediate (hence the enzyme’s original classification as EC 4.2.1.16, threonine dehydratase), followed by tautomerization to an imine form and hydrolysis of the C-N bond [3,5]. The latter reaction, which can occur spontaneously, is also be catalysed by EC 3.5.99.10, 2-iminobutanoate/2-iminopropanoate deaminase [5]. The enzymes from a number of sources also act on L-serine, cf. EC 4.3.1.17, L-serine ammonia-lyase.

Links to other databases:

BRENDA, EAWAG-BBD, EXPASY, Gene, KEGG, MetaCyc, PDB, CAS registry number: 774231-81-1

References:

1.	Cohn, M.S. and Phillips, A.T. Purification and characterization of a B6-independent threonine dehydratase from Pseudomonas putida. Biochemistry 13 (1974) 1208–1214. [PMID: 4814721]
2.	Nishimura, J.S. and Greenberg, D.M. Purification and properties of L-threonine dehydrase of sheep liver. J. Biol. Chem. 236 (1961) 2684–2691. [PMID: 14479973]
3.	Phillips, A.T. and Wood, W.A. The mechanism of action of 5′-adenylic acid-activated threonine dehydrase. J. Biol. Chem. 240 (1965) 4703–4709. [PMID: 5321308]
4.	Shizuta, Y., Nakazawa, A., Tokushige, M. and Hayaishi, O. Studies on the interaction between regulatory enzymes and effectors. 3. Crystallization and characterization of adenosine 5′-monophosphate-dependent threonine deaminase from Escherichia coli. J. Biol. Chem. 244 (1969) 1883–1889. [PMID: 4889010]
5.	Lambrecht, J.A., Flynn, J.M. and Downs, D.M. Conserved YjgF protein family deaminates reactive enamine/imine intermediates of pyridoxal 5′-phosphate (PLP)-dependent enzyme reactions. J. Biol. Chem. 287 (2012) 3454–3461. [DOI] [PMID: 22094463]

[EC 4.3.1.19 created 1961 as EC 4.2.1.16, transferred 2001 to EC 4.3.1.19, modified 2014]