Threonine dehydrogenase

Tiessel, T, Thompson, R., Zieske, L. R., Menendez, M., and Davis, L. (1986). Interaction between L-threonine dehydrogenase and aminoacetone synthetase and mechanisms of artiinuacetone production. /. Bjuf. Citon. 261,16428-16437. 

Threonine can be broken down by two separate pathways. Serine dehydratase catalyzes the conversion of threonine to 2-ketobut ate plus an ammonium ion 2-ketobutyrate is then converted by branched-chain keto add (BCKA) dehydrogenase to propionyl-CoA plus carbon dioxide. Propionyl-CoA catabolism is described later in this chapter. Threonine can also be broken down by a complex that has been suggested to be composed of threonine dehydrogenase and acetoacetone synthase (Tressel et ah, 1986). Here, threonine catabolism results in the production of acetyl-CoA plus glycine. 

Threonine. In the major degradative pathway, threonine is oxidized by threonine dehydrogenase to form a-amino-/3-ketobutyrate. The latter molecule is... 

Fig. 1. Bio thetic pathways for the essential aspartate-family amino adds. The numbers represent enzymes catalyzing the reaction 1, aspartate kinase 2, homoserine dehydrogenase 3, homoserine kinase 4, threonine thase 5, threonine dehydrogenase 6, acetolactate thase 7, dihydrodipicolinate thase 8, diaminopimelate decarboiylase.

Threonine dehydrogenase tdh Consume threonine to produce glycine in E. coli... 

Fig. 1. Modification of plant metabolic pathways for the synthesis of poly(3HB) and poly(3HB-co-3HV). The pathways created or enhanced by the expression of transgenes are highlighted in bold, while endogenous plant pathways are in plain letters. The various transgenes expressed in plants are indicated in italics. The ilvA gene encodes a threonine deaminase from E. coli. The phaARe, phaBRe, and phaCRe genes encode a 3-ketothiolase, an aceto-acetyl-CoA reductase, and a PHA synthase from R. eutropha, respectively. The btkBRe gene encodes a second 3-ketothiolase isolated from R. eutropha which shows high affinity for both propionyl-CoA and acetyl-CoA [40]. PDC refers to the endogenous plant pyruvate dehydrogenase complex...

Fig. 3. Generation of propionyl-CoA from the isoleucine biosynthetic pathway. The intermediate 2-ketobutyrate can be decarboxylated by either the 2-oxoacid dehydrogenase complex or at low efficiency by the pyruvate dehydrogenase complex. Inhibition of the threonine deaminase by isoleucine and of the acetolactate synthase by herbicides are indicated with dashed arrows...

This enzyme [EC 1.5.1.17] catalyzes the reversible reaction of 2,2 -iminodipropanoate with water and NAD+ to produce alanine, pyruvate and NADH. In the reverse reaction, alanine can be replaced as a substrate by cysteine, serine, or threonine. Glycine acts very slowly as a substrate (that is, the reaction catalyzed by strombine dehydrogenase). 

Starnes, W.L. Munk, P. Maul, S.B. Cunningham, G.N. Cox, D.J. Shive, W. Threonine-sensitive aspartokinase-homoserine dehydrogenase complex, amino acid composition, molecular weight, and subunit composition of the complex. Biochemistry, 11, 677-687 (1972)... 

Veron, M. Falcoz-Kelly E Cohen, G.N. The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K12. The two catalytic activities are carried by two independent regions of the polypeptide chain. Eur. J. Biochem., 28, 520-527 (1972)... 

Azevedo, R.A. Smith, R.J. Lea, P.J. Aspartate kinase regulation in maize Evidence for co-purification of threonine-sensitive aspartate kinase and homoserine dehydrogenase. Phytochemistry, 31, 3731-3734 (1992)... 

Paris, S. Wessel, P.M. Dumas, R. Overproduction, purification, and characterization of recombinant bifunctional threonine-sensitive aspartate kinase-homoserine dehydrogenase from Arabidopsis thaliana. Protein Expr. Purif., 24, 105-110 (2002)... 

Paris, S. Viemon, C. Curien, G. Dumas, R. Mechanism of control of Arabidopsis thaliana aspartate kinase-homoserine dehydrogenase by threonine. J. Biol. Chem., 278, 5361-5366 (2003)... 

Marshall, V. M. and Cole, W. M. 1983. Threonine aldolase and alcohol dehydrogenase activities in Lactobacillus bulgaricus and Lactobacillus acidophilus and their contribution to flavour production in fermented foods. J. Dairy Res. 50, 375-379. 

Pyridoxol (vitamin Bg). Again 1-deoxyxylulose 5-P serves as a precursor.378 In E. coli only two genes have been implicated in the condensation of this compound with 4-(phosphohydroxy)-L-threonine (Fig. 25-21, step/) 378a One is an NAD+-dependent dehydrogenase that acts on the second substrate prior to the condensation. Significant differences from the path-... 

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