Threonine pyruvate formation from

Figure 23.22. Pyruvate Formation from Amino Acids. Pymvate is the point of entry for alanine, serine, cysteine, glycine, threonine, and tryptophan.

On the other hand, a-transaminases have been used extensively in the production of amino acids through kinetic resolution and asymmetric synthesis. While many studies rely on the use of an excess of cosubstrate to drive the reaction to completion, some multienzymatic approaches have been developed as well. As an example, aspartate has been used as an amino donor in a multienzymatic synthesis of L-2-aminobutyrate from L-threonine (Scheme 4.8). ° The rather complex multistep sequence started with the in situ formation of 2-ketobutyrate from L-threonine catalysed by threonine deaminase (ThrDA) from E. coli. A tyrosine transaminase (lyrAT) from E. coli converted 2-ketobutyrate and L-aspartie acid to L-2-aminobutyrate and oxaloacetate, which spontaneously decarboiq lated to give pyruvate. Since the... 

The use of chiral complexes gives rise to enantioselectivity of carbon—carbon bond formation and this phenomenon has also been applied to resolution54 and enantioselective deuteration55 56 of amino acids. Both the kinetic acidity of the a-methylene protons and the enantioselectivity of bond formation are greatly enhanced by the formation of chiral complexes (32) and (33) of imines derived from the amino acid and salicylaldehyde or pyridoxal respectively.57-59 Similar use has been made of inline complexes (34) derived from pyruvic acid and the amino acid.60 61 Very recently, an asymmetric synthesis of threonine has been achieved using the chiral imine complex (35).62... 

Threonine dehydratase catalyzes the formation of 2-ketobutyrate from threonine, and pyruvate from serine. This assay can be used to examine the reaction in the presence of both substrates. 

Diacetyl, and its reduction products, acetoin and 2,3-butanediol, are also derived from acetaldehyde (Fig 8D.7), providing additional NADH oxidation steps. Diacetyl, which is formed by the decarboxylation of a-acetolactate, is regulated by valine and threonine availability (Dufour 1989). When assimilable nitrogen is low, valine synthesis is activated. This leads to the formation of a-acetolactate, which can be then transformed into diacetyl via spontaneous oxidative decarboxylation. Because valine uptake is suppressed by threonine, sufficient nitrogen availability represses the formation of diacetyl. Moreover, the final concentration of diacetyl is determined by its possible stepwise reduction to acetoin and 2,3-butanediol, both steps being dependent on NADH availability. Branched-chain aldehydes are formed via the Ehrlich pathway (Fig 8D.7) from precursors formed by combination of acetaldehyde with pyruvic acid and a-ketobutyrate (Fig 8D.7). 

Apart from sotolon, the other compounds in Fig. 5 can be explained as the products of a Maillard reaction, and their carbon skeletons simply originate from the active Amadori intermediate in other words, they still preserve the straight carbon chain structure of monosaccharides. In spite of being a simple Cg lactone, sotolon has a branched carbon skeleton, which implies another formation process in the Maillard reaction. Sulser e al.(6) reported that ethyl sotolon (ll) was prepared from threonine with sulfuric acid, and that 2-oxobutyric acid, a degradation product of threonine, was a better starting material to obtain II. This final reaction is a Claisen type of condensation, which would proceed more smoothly under alkaline conditions. As we(lO) obtained II from 2-oxobutyric acid (see figure 6) with a high yield in the presence of potassium carbonate in ethanol, a mixed condensation of 2-oxobutyric and 2-oxo-propanoic (pyruvic) acids was attempted under the same conditions, and a mixture of sotolon (22% yield) and II were obtained however, the... 

One aspect of archaeal corrinoid biosynthesis that remains to be verified is the formation of the l-amino-2-propanol linker in the lower ligand loop of the corrinoid. Possible sources include the reductive amination of lactaldehyde, the reductive amination of pyruvate, or the decarboxylation of threonine. Several bacteria have been shown to directly incorporate N-labeled threonine into aminopropanol and coenzyme Bi2- A threonine decarboxylase (CobD) has been detected in Streptomyces griseus and Salmonella typhimuriumP Studies with CobD from S. typhimurium LT2 were able to clearly demonstrate the decarboxylation of threonine-phosphate however, the timing of the decarboxylation could not be demonstrated and may occur prior to or after addition of the threonine-P to the corrin ring. " ... 

In at least one archaea, M. thermoautotrophicus, threonine does not appear to be the precursor to the aminopropanol moiety of cobamide. Labeling patterns of aminopropanol in this organism were found to be similar to pyruvate or lactate and not threonine, leading Eisenreich and Bacher to propose a reductive amination pathway from pyruvate for aminopropanol formation. ... 

Grout (206) a bios3mthetic correlation between trichodesmic and echimi-dinic acids and hence the C5 unit in monocrotalic and the Cio adipic acids. He envisaged the C5 unit common to both acids as being developed from pyruvate, threonine, and methionine or formate. 

While the 2-oxobutyrate needed for isoleucine formation is shown as originating from threonine in Eig. 24-17, bacteria can often make it in other ways, e.g., from glutamate via p-methylaspartate (Eig. 24-8) and transamination to the corresponding 2-oxoacid. It can also be made from pyruvate by chain elongation using acetyl-CoA (Eig. 17-18) citramalate and mesa-conate (Eig. 24-8) are intermediates. This latter pathway is used by some methanogens as are other alternative routes. The first step unique to the biosynthetic pathway to leucine is the reaction of the... 

L-lsoieucine, lie L-a-amino-P-methylvaleric acid, CH3-CH2-CH(CH3)-CH(NH2)-C00H, an aliphatic, neutral amino acid found in proteins. He is found in relatively large amounts in hemoglobin, edestin, casein and serum proteins, and in sugar beet molasses, from which it was first isolated in 1904 by F. Ehrlich. It is an essential dietary amino acid, and is both glu-coplastic (degradation via propionic acid) and keto-plastic (formation of acetate) (see Leucine), The biosynthesis of He starts with oxobutyrate and pyruvate. Oxobutyrate is synthesized by deamination of L-threonine by threonine dehydratase (threonine de-... 

Poly-3-hydroxybutyrate-co-3-hydroxyvalerate [P(3HB-co-3HV)] copolymers have a variety of uses as single use, bulk-commodity plastics, in the marine environment and in biomedical applications (2/). Normally, P(3HB-co-3HV) is synthesized in bacteria grown on a mixture of glucose and propionate (22). Although demonstrated in plants. Figure 1C shows a pathway which could potentially be used in bacteria for the conversion of threonine (derived from the TCA cycle) to 3-hydroxyvalerate by threonine deaminase, IlvA, to 2-ketobutyrate, followed by reduction to propionyl-CoA by pyruvate dehydrogenase. BktB then catalyzes the formation of the 3-(7 )-hydroxyvaleryl-CoA substrate which can be polymerized into a P(3HB-co-3HV) copolymer (23). 

---