Disease relevance of oxobutyrate

• Two different pyridoxal 5'-phosphate-containing l-threonine deaminases (EC 4.3.1.19), biosynthetic and biodegradative, which catalyze the deamination of l-threonine to alpha-ketobutyrate, are present in Escherichia coli and Salmonella typhimurium [1].
• The enzymic dehydration of threonine to alpha-ketobutyrate measured by steady-state kinetics, performed at 20 degrees C in 0.05 M potassium phosphate, pH 7.5, is described by a Hill coefficient, nH, of 2.3 and a K0.5 of 8.0 mM [2].
• With the aim of obtaining regulatorily altered mutants of the threonine dehydratase of Corynebacterium glutamicum, amino acids were specifically exchanged and a new biological system of mutant selection was developed, based on the intoxication of Escherichia coli by ketobutyrate, which is the dehydratase reaction product [3].
• To gain insight into this unusual ring-opening reaction, we have solved the crystal structures of ACC deaminase from Pseudomonas sp. ACP in complex with substrate ACC, an inhibitor, 1-aminocyclopropane-1-phosphonate (ACP), the product alpha-ketobutyrate, and two d-amino acids [4].
• The transient derangement of the energy metabolism after glucose addition to starved ascites tumour cells by preventable by simultaneous addition of pyruvate or 2-oxobutyrate, or by preincubating the cells in the presence of glucose [5].

High impact information on oxobutyrate

• With kidney cytosol, DCVHcy or the analogue S-(2-benzothiazolyl)-L-homocysteine (BTHcy) is not metabolized to 2-ketobutyrate, but 2-mercaptobenzothiazole is a metabolite of BTHcy and the Vmax for its formation is enhanced by addition of 2-ketobutyrate [6].
• The sigmoidal kinetics of alpha-ketobutyrate production catalyzed by threonine deaminase are shifted in the presence of the feedback inhibitor isoleucine and the activator valine to control carbon flow through branched-chain amino acid biosynthesis in Escherichia coli [7].
• The reaction of L-methionine sulfoximine with gamma-cystathionase yields 1 mol each of alpha-ketobutyrate and methane sulfinimide; the latter is hydrolyzed almost exclusively to methane sulfinic acid [8].
• Enzyme studies showed that TdcE has both pyruvate formate-lyase and 2-ketobutyrate formate-lyase activity, whereas the TdcD protein is a new propionate/acetate kinase [9].
• Binding of the ketobutyrate substrate is accompanied by closure of the active site specificity loop, whereas the steroid substrate does not appear to require closure for binding [10].

Chemical compound and disease context of oxobutyrate

• Conversion of Escherichia coli pyruvate oxidase to an 'alpha-ketobutyrate oxidase' [11].
• Phosphoenolpyruvate carboxylase (EC 4.1.1.31) of Escherichia coli was found to catalyze the cleavage reaction of phosphoenol-alpha-ketobutyrate, a potent competitive inhibitor with the substrate, to yield inorganic phosphate and alpha-ketobutyrate [12].
• Biochemical and genetic analyses of the bacterium Salmonella typhimurium suggest that accumulation of alpha-ketobutyrate partially mediates the herbicidal activity of acetolactate synthase inhibitors [13].
• Acetolactate synthase small subunit encoding ilvN genes from the parental Streptomyces cinnamonensis strain and mutants resistant either to valine analogues or to 2-ketobutyrate were cloned and sequenced [14].
• The present investigation examined DL-threonine, D-threonine and 2-oxobutyrate conversion into propionate and 2-hydroxybutyrate by various type strains and clinical isolates of Fusobacterium [15].

Biological context of oxobutyrate

• We conclude that both intramitochondrial complexes are responsible for oxidative decarboxylation of 2-oxobutyrate [16].
• By localized random mutagenesis of residues chosen on the basis of a modelled active site, we obtained several PoxB enzymes that had a markedly decreased activity with the natural substrate, pyruvate, but retained full activity with 2-oxobutanoate [11].
• The phosphorylation state of both complexes in extracts of mitochondria from rat liver, kidney, heart and skeletal muscle was shown to influence oxidative decarboxylation of 2-oxobutyrate [16].
• Tissue distribution of alpha-ketobutyrate dehydrogenase activity relative to liver activity was (in percent): liver, 100; heart, 127; brain, 63; kidney, 57; skeletal muscle, 38; and small intestine, 7 [17].
• The enzyme is characterized by a broad substrate specificity 2-ketoisocaproate and 2-ketobutyrate being the substrates with the higher Vmax/Km [18].

Anatomical context of oxobutyrate

• Hydroxyapatite chromatography of extracts of mitochondria from rat liver revealed only two peaks of oxidative decarboxylation of 2-oxobutyrate, with one peak associated with PDH and the other with BCODH [16].
• These results indicated that in human skin fibroblasts the decarboxylation of 2-oxobutyrate is catalysed by an enzyme system different from the pyruvate dehydrogenase complex [19].
• Based on these observations, the present study examined the effect of alpha-ketobutyrate on palmitic acid and pyruvate metabolism in hepatocytes isolated from fed rats. alpha-Ketobutyrate (10 mM) inhibited the oxidation of palmitic acid by 34% [20].

Associations of oxobutyrate with other chemical compounds

• Previous studies have proposed that some HI0719 homologues may act on small molecules in the isoleucine biosynthetic path and, if this is correct, the ligand screening results presented here suggest that the interaction most likely occurs with 2-ketobutyrate and/or its unstable enamine precursor [21].
• We overcome this problem by preparing a protein using a 98% D2O cell culture medium containing 3-(13)C pyruvic acid, 50-60% deuterated at the 3-position, and 4-(13)C 2-ketobutyric acid, 98% and 62% deuterated at the 3- and 4-positions, respectively [22].
• Inhibitory antibodies to BCODH and an inhibitor of PDH (3-fluoropyruvate) were used with mitochondrial extracts to determine the relative contribution of both complexes to oxidative decarboxylation of 2-oxobutyrate [16].
• Importantly, much smaller effects were observed for the kinetic parameters of reactions with the alternate substrates L-vinylglycine (L-VG) (deamination to form alpha-ketobutyrate and ammonia) and L-alanine (transamination to form pyruvate), which have uncharged side chains [23].
• Alternatively, in the threonine dehydratase pathway, the 1-carbon ends up in alpha-ketobutyrate, which is oxidized in the mitochondria to CO(2) [24].

Gene context of oxobutyrate

• Based on these results, we propose a model to explain the regulation of the isoleucyl- and valyt -tRNA synthetases in which transient inhibition of the synthetase enzyme activities by threonine deaminase and 2-ketobutyrate increases the expression of ileS and valS , the structural genes for isoleucyl- and valyt -tRNA synthetase, respectively [25].
• L-serine dehydratase (SDH), a member of the beta-family of pyridoxal phosphate-dependent (PLP) enzymes, catalyzes the deamination of L-serine and L-threonine to yield pyruvate or 2-oxobutyrate [26].
• Although urocanase from Ps. testosteroni is strongly inhibited by NaBH4, no evidence could be obtained for the presence of covalently bound 2-oxobutyrate as a prosthetic group; this is in contrast with findings elsewhere for urocanase from Pseudomonas putida [27].
• In Met-dependent tumour cells with defective MTA phosphorylase, 2-oxobutanoate production would exceed that of MTOB [28].
• IpOHA has strong initial effects at lower concentrations than does SMM and leads to increases both in the acetohydroxy acid substrates of KARI and, surprisingly, in ketobutyrate [29].

Analytical, diagnostic and therapeutic context of oxobutyrate

• A sensitive assay, involving the use of high performance liquid chromatography, was developed to measure the small amounts of alpha-ketobutyrate produced [30].

References