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EC 4.3.1.19 Details
EC number
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)
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)
CAS registry number
774231-81-1
Comment
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.
History
created 1961 as EC 4.2.1.16, transferred 2001 to EC 4.3.1.19, modified 2014
EC Tree
4.3.1.8 created 1972, modified 1982, modified 1989, deleted 2003
4.3.1.21 created 1965 as EC 4.2.1.26, transferred 2002 to EC 4.3.1.21, deleted 2004