2-Oxobutyrate from threonine

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... 

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... 

Oxocarboxylic acids are major products of the metabolism of proteins, lipids and carbohydrates, and also arise as intermediates in fermentation processes, as products of other enz)miatic reactions, which are not linked with the metabolism of major nutrients, and also as products of non-enzymatic reactions. They usually occur in low concentrations in aU foods of animal and vegetable origin. Oxoacids are polar and non-volatQe compounds, but some of their reaction products are important odour-active substances in foods. An example is 5-ethyl-3-hydroxy-4-methyl-5H-furan-2-one (abhexon), which appears in acid protein hydrolysates from threonine via 2-oxobutyric acid. 

Hofmann and Schieberle (1996) suggested hydroxyacetaldehyde and 2,3-butanedione as possible precursors of this odorant lactone. A mechanism of formation (in vin jaune ) has been proposed by Guichard et al. (1998) by transformation of threonine (present in coffee) into 2-oxobutyric acid (which can also be derived from carbohydrates), condensation with acetaldehyde and cyclization. 

Optically pure opine-tjrpe secondary amine carboxylic acids were also synthesized from amino acids and their analogs, such as L-methionine, L-isoleucine, L-leucine, L-valine, L-phenylalanine, L-alanine, L-threonine, L-serine, and L-phenylalaninol, and a-keto acids, such as glyoxylic, pyruvic, and 2-oxobutyric acids, using the enzyme with regeneration of NADH with FDH from Moraxella sp. C-1 [13]. The absolute configuration of the nascent asymmetric center of the opines was of the D stereochemistry with > 99.9% e.e. One-pot synthesis of N-[l-D-(carboxyl)ethyl]-L-phenylalanine from phenylpyruvic and pyruvic acid by using ODH, FDH, and phenylalanine dehydrogenase (PheDH) from Bacillus sphaericus... 

Regulation of the synthesis of the branched-chain amino acids, like that of the aspartate family, can be viewed in a temporal framework (Fig. 8). However, the nature of the controls associated with the pathway enzymes do not necessarily suggest an obligatory sequence of regulatory interactions. The sequence illustrated in Fig. 8 assumes that each of the end-products would initially be synthesized from its respective precursors. As isoleucine biosynthesis is reduced by inhibition of threonine dehydratase, the competition between pyruvate and 2-oxobutyrate for the active site of acetohydroxyacid synthase would be diminished. This could result in an increased rate of synthesis of leucine and valine (Fig. 8, 2). Leucine would eventually inhibit isopropylmalate synthase and, to a lesser extent, acetohydroxyacid synthase (Fig. 8, 3). The reduced flow of carbon through the pathway would be utilized for the synthesis of valine. As the concentration of valine increased, the activity of acetohydroxyacid synthase would be sharply curtailed due to... 

The enzyme catalyzing reaction 1 is threonine dehydratase. As described above for serine dehydratase, an enzyme having activity towards both serine and threonine has been found in spinach leaves (Sharma and Mazumder, 1970). Dougall (1970) has also reported a threonine dehydratase in extracts from Paul s Scarlet Rose tissue cultures. The oxidative decarboxylation of the 2-oxobutyrate would lead to propionate (reaction 2) which could then be oxidized via the pathway demonstrated by Giovanelli and Stumpf (1958). 

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-... 

L-Isoleucine originates from 2-oxobutyric acid, a threonine derivative and activated acetaldehyde (C 4) as outlined in Fig. 196. Both compounds condense to form tx-aceto-a-hydroxybutyric acid from which 2,3-dihydroxy-3-methyl-... 

Greatly increased lactic aciduria is generally associated with an increased excretion of 2-hydroxy-n-butyric acid (Pettersen et al., 1973 Landaas and Pettersen, 1975) irrespective of the underlying cause of the increased lactate excretion. This acid is thought to arise from 2-oxobutyric acid, a metabolite of methionine, homocystine, cystathionine, serine and threonine, owing to the effect of the changes in NADH/NAD+ ratio in lactic acidosis (Pettersen etaL, 1973). The occurrence of 2-hydroxybutyrate in urine would thus imply an imbalance in cytosolic NADH/NAD and this metabolite may be of value in the further assessment of patients with lactic acidosis. 

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