Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Multienzyme Complexes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed1997

Targeted disruption of the murine dihydrolipoamide dehydrogenase gene (Dld) results in perigastrulation lethality.

The Dld gene product, known as dihydrolipoamide dehydrogenase or the E3 component, catalyzes the oxidation of dihydrolipoyl moieties of four mitochondrial multienzyme complexes: pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, branched-chain alpha-ketoacid dehydrogenase, and the glycine cleavage system. Deficiency of E3 activity in humans results in various degrees of neurological dysfunction and organic acidosis caused by accumulation of branched-chain amino acids and lactic acid. In this study, we have introduced a null mutation into the murine Dld gene (Dldtm1mjp). The heterozygous animals are shown to have approximately half of wild-type activity levels for E3 and all affected multienzyme complexes but are phenotypically normal. In contrast, the Dld-/- class dies prenatally with apparent developmental delay at 7.5 days postcoitum followed by resorption by 9.5 days postcoitum. The Dld-/- embryos cease to develop at a time shortly after implantation into the uterine wall when most of the embryos have begun to gastrulate. This null phenotype provides in vivo evidence for the requirement of a mitochondrial oxidative pathway during the perigastrulation period. Furthermore, the early prenatal lethal condition of the complete deficiency state may explain the low incidence of detectable cases of E3 deficiency in humans.

Animals↗
PubMed1977

Fatty acid synthetase activity in Mycobacterium smegmatis. Characterization of the acyl carrier protein-dependent elongating system.

Mycobacterium smegmatis extracts contain two fatty acyl synthetase systems (Brindley, D.N., Matsumura, S. and Bloch, K. (1966) Nature 224, 666-669). One is the extensively studied multienzyme complex, (molecular weight 1.39 - 10(6)) which produces shorter C16 and C18) and longer (C24 and higher) fatty acids in a bimodal pattern. The second synthetase is acyl carrier-protein (ACP) dependent and elongates the CoA derivatives of C12 and longer chains. In contrast to the type I synthetase which also extends long fatty acyl chains, the ACP-dependent system produces homologous fatty acids up to 30 carbon atoms long in approximately equal proportions. Other properties which distinguish the ACP-dependent system from the multienzyme complex include the resistance to high concentrations of palmitoyl-CoA and to low ionic strength and the lack of stimulation by mycobacterial polysaccharides. The possibility that the two fatty acid synthetases are complimentary in their function is discussed.

Adenosine Triphosphate↗
PubMed1979

Identity of malonyl and palmitoyl transferase of fatty acid synthetase from yeast. Functional interrelationships between the acyl transferases.

Functional interrelationships between the acyl transferases of yeast fatty acid synthetase were investigated. In binding assays with synthetase modified by 5,5'-dithiobis(2-nitrobenzoic acid), 4--5 malonyl transferase entities per multienzyme complex molecule could be titrated. In the presence of palmitoyl-CoA these malonyl transferases were found inaccessible to malonyl-CoA, whereas the acetyl transferases were reactive towards acetyl-CoA. Between four and five palmitoyl transferase entities per synthetase equivalent were found reactive towards palmitoyl-CoA, the palmitoyl binding being inhibited by malonyl-CoA. Following palmitoyl binding the acetyl transferases were found towards acetyl-CoA. Substrate model assays were consistent with these data. It is concluded that malonyl and palmitoyl transferases are closely coupled enzyme components of the multienzyme complex which are fairly independent of the acetyl transferase entities. The molecular basis for the observed coupling will be given in the following paper.

Acyltransferases↗
PubMed1978

A possible model for the structure of the Neurospora carbamoyl phosphate synthase-aspartate carbamoyl transferase complex enzyme.

The pyrimidine-3 locus of Neurospora crassa specifies a multienzyme complex comprising pyrimidine-specific carbamoyl phosphate synthase (CPSpyr) and aspartate carbamoyl transferase (ACT). It appears to be divided into a translationally proximal CPS-specific region and a distal ACT-specific region. Levels of complementation for ACT activity between pairs of four pyr-3 CPS+ ACT- mutants showed a range from 12% to 68% of the wild-type level of the enzyme. This is interpreted as interallelic complementation, contradicting certain earlier suggestion of two dissimilar ACT subunits. Proteolysis of an extract from a heterokaryon formed from two of the above CPS+ ACT- alleles (alpha and beta) did not lead to loss of ACT activity, but led to the formation of a fragment with ACT activity with a similar molecular weight (92,000 daltons) to that produced in extracts of wild type strain. The pyr-3 polar mutant 43-174 which is enzymatically CPS+ ACT- and which fails to complement with any other CPS+ ACT- alleles, thus suggesting its location towards the proximal end of the ACT region, has CPS activity associated with a form of 180,000 daltons molecular weight. These findings are used to contruct a model for structure of the native enzyme complex.

Amino Acid Sequence↗
PubMed1991

Cloning, sequence and transcriptional analysis of the structural gene for LPD-3, the third lipoamide dehydrogenase of Pseudomonas putida.

The third lipoamide dehydrogenase structural gene of Pseudomonas putida, lpd3, was isolated from a library of P. putida PpG2 DNA cloned in Escherichia coli TB1. The nucleotide sequence of lpd3 and its flanking regions indicate that lpd3 is not part of an operon, which is unique for a prokaryotic lipoamide dehydrogenase. An open reading frame was found 207 bases upstream from the start of transcription, but is encoded on the strand opposite lpd3. There is no evidence of an open reading frame immediately downstream from lpd3. The coding region of lpd3 consists of 1401 bp, providing for 466 amino acids plus a stop codon with a G/C content of 62.4%. The transcriptional start site was located 33-bp upstream from the start of translation. The third lipoamide dehydrogenase (LPD-3) shares amino acid identity with the other two lipoamide dehydrogenases of P. putida, 45% with that of the 2-oxoglutarate dehydrogenase and pyruvate multienzyme complexes, and 45.9% with the lipoamide dehydrogenase of the branched-chain oxoacid complex. LPD-3 is more closely related to eukaryotic lipoamide dehydrogenases since it has 53.6% amino acid sequence identity with pig and human lipoamide dehydrogenases and 51.1% identity with yeast lipoamide dehydrogenase. LPD-3 was not produced in wild-type P. putida PpG2 under a variety of growth conditions. However, LPD-3 was produced in P. putida PpG2 carrying pSP14, a pKT240-based clone with the entire lpd3 gene plus 104 bases of the leader. The only demonstrated role of LPD-3 in P. putida is as a substitute for lipoamide dehydrogenase of the 2-oxoglutarate dehydrogenase and pyruvate multienzyme complexes when the latter is inactive or missing.

Amino Acid Sequence↗
PubMed1974

Revertants and secondary arom-2 mutants induced in non-complementing mutants in the arom gene cluster of Neurospora crassa.

Extensive genetical and biochemical studies have been performed with revertants and secondary arom-2 mutants induced in two different primary non-complementing mutants which map within the arom gene cluster of Neurospora crassa. These studies indicate that mutant M54 but not M25 can revert by super-suppressor mutations in unlinked genes, thus confirming previous evidence that M54 contains a nonsense codon. At least three new super suppressors of M54 have been detected. All four super suppressors (including one previously detected) when combined with M54 result in high levels of all five of the arom enzymic activities in the form of arom multienzyme complexes very similar to (but not necessarily identical with) that in wild type (WT).-Evidence has also been obtained that the two non-complementing mutants can yield revertants which appear to result from true back mutations and produce arom aggregates essentially indistinguishable from that of WT. In addition, M25, but not M54, when plated on quinic acid yields revertants (secondary mutants) some of which are phenotypically indistinguishable from arom-2 primary mutants and others of which, although also mapping within the arom-2 gene, exhibit unusual properties. Genetic evidence indicates that the M25 secondary mutants are localized within the arom-2 gene, but that they arise from mutational events more complex than ones resulting in single base pair changes in the M25 codon.-The recovery of secondary arom-2 mutants as revertants of non-complementing arom mutants provides strong evidence, independent of earlier recombination data, that non-complementing arom mutants are located within the arom-2 structural gene of the arom gene cluster. In addition, the occurrence and characteristics of these secondary arom-2 mutants provide strong evidence, independent of the results with nonsense suppressors, that the arom gene cluster is transcribed, beginning with the arom-2 gene, as a single polycistronic messenger ribonucleic acid (mRNA) molecule which is subsequently translated into the arom multienzyme complex.

Alcohol Oxidoreductases↗
PubMed1995

Lysyl-tRNA synthetase.

Lysyl-tRNA synthetase catalyses the formation of lysyl-transfer RNA, Lys-tRNA(Lys), which then is ready to insert lysine into proteins. Lysine is important for proteins since it is one of only two proteinogenic amino acids carrying an alkaline functional group. Seven genes of lysyl-tRNA synthetases have been localized in five organisms, and the nucleotide and the amino acid sequences have been established. The lysyl-tRNA synthetase molecules are of average chain lengths among the aminoacyl-tRNA synthetases, which range from about 300 to 1100 amino acids. Lysyl-tRNA synthetases act as dimers; in eukaryotes they can be localized in multienzyme complexes and can contain carbohydrates or lipids. Lysine tRNA is recognized by lysyl-tRNA synthetase via standard identity elements, namely anticodon region and acceptor stem. The aminoacylation follows the standard two-step mechanism. However the accuracy of selecting lysine against the other amino acids is less than average. The first threedimensional structure of a lysyl-tRNA synthetase worked out very recently, using the enzyme from the Escherichia coli lysU gene which binds one molecule of lysine, is similar to those of other class II synthetases. However, none of the reaction steps catalyzed by the enzyme is clarified to atomic resolution. Thus surprising findings might be possible. Lysyl-tRNA synthetase and its precursors as well as its substrates and products are targets and starting points of many regulation circuits, e.g. in multienzyme complex formation and function, dinucleoside polyphosphate synthesis, heat shock regulation, activation or deactivation by phosphorylation/dephosphorylation, inhibition by amino acid analogs, and generation of antibodies against lysyl-tRNA synthetase. None of these pathways is clarified completely.

Amino Acid Sequence↗
PubMed1992

Beta-oxidation as channeled reaction linked to citric acid cycle: evidence from measurements of mitochondrial pyruvate oxidation during fatty acid degradation.

1. The kinetics of mitochondrial mammalian pyruvate dehydrogenase multienzyme complex (PDHC) is studied by the formation of CO2 using tracer amounts of [1-14C]pyruvate. It is found that the Hill plot results in a (pseudo-)cooperativity with a transition of n-1----3 at a pyruvate concentration about Ks. 2. Addition of L-carnitine, octanoate, palmitoyl-CoA or palmitate + L-carnitine + fatty acid-binding protein results in a Hill coefficient of n = 2 following the kinetics of pyruvate oxidation. 3. Addition of fatty acid-binding protein to an assay system oxidizing palmitate in presence of L-carnitine alters the pattern of the kinetics in the Hill plot so that an apparently lower level of L-carnitine is necessary for the reaction course of beta-degradation. 4. It is concluded that beta-degradation is a coordinated, multienzyme-complex based mechanism tightly linked to citric acid cycle and it is proposed that L-carnitine is actively involved into the reaction and not only functioning as carrier-molecule for transmembrane transport.

Animals↗
PubMed1997

Physical and Kinetic Evidence for an Association between Sucrose-Phosphate Synthase and Sucrose-Phosphate Phosphatase.

The possible formation of a multienzyme complex between sucrose (Suc)-phosphate synthase (SPS) and Suc-phosphate phosphatase (SPP) was examined by measuring the rates of Suc-6-phosphate (Suc-6-P) synthesis and hydrolysis in mixing experiments with partially purified enzymes from spinach (Spinacia oleracea) and rice (Oryza sativa) leaves. The addition of SPP to SPS stimulated the rate of Suc-6-P synthesis. SPS inhibited the hydrolysis of exogenous Suc-6-P by SPP when added in the absence of its substrate (i.e. UDP-glucose) but stimulated SPP activity when the SPS substrates were present and used to generate Suc-6-P directly in the reaction. Results from isotope-dilution experiments suggest that Suc-6-P was channeled between SPS and SPP. A portion of the SPS activity comigrated with SPP during native polyacrylamide gel electrophoresis, providing physical evidence for an enzyme-enzyme interaction. Taken together, these results strongly suggest that SPS and SPP associate to form a multienzyme complex.

Journal Article↗
PubMed1998

Redox-dependent acetyl transfer partial reaction of the acetyl-CoA decarbonylase/synthase complex: kinetics and mechanism.

Acetyl-CoA decarbonylase/synthase (ACDS) is a multienzyme complex that plays a central role in energy metabolism in Methanosarcina barkeri grown on acetate. The ACDS complex carries out an unusual reaction involving net cleavage of the acetyl C-C and thioester bonds of acetyl-CoA. The overall reaction is composed of several partial reactions, one of which involves catalysis of acetyl group transfer. To gain insight into the overall reaction, a study was carried out on the kinetics and mechanism of the acetyltransferase partial reaction. Analysis by HPLC was used to quantify rates of acetyl transfer from acetyl-CoA both to 3'-dephospho-CoA and, by isotope exchange, to 14C-labeled CoA. Acetyl transfer activity was observed only under strongly reducing conditions, and was half-maximal at -486 mV at pH 6.5. The midpoint activation potential became increasingly more negative as the pH was increased, indicating the involvement of a protonation step. Cooperative dependence on acetyl-CoA concentration was exhibited in reactions that contained incompletely reduced enzyme; however, under redox conditions supporting maximum activity, hyperbolic kinetics were found. A ping-pong steady state kinetic mechanism was established, consistent with formation of an acetyl-enzyme intermediate. Analysis of the inhibitory effects of CoA on acetyl transfer to 3'-dephospho-CoA provided values for KiCoA of 6.8 microM and for Kiacetyl-CoA of 45 microM; isotope exchange analyses yielded values of 32 and 120 microM, respectively. Two separate measures of stability yielded values for the free energy of hydrolysis of the acetyl-enzyme intermediate of -9.6 and -9.3 kcal/mol, an indication of a high-energy bonding interaction in the acetyl-enzyme species. Implications for the mechanism of C-C bond cleavage are discussed.

Acetyl Coenzyme A↗
PubMed1995

Complementation of defective leucine decarboxylation in fibroblasts from a maple syrup urine disease patient by retrovirus-mediated gene transfer.

Maple syrup urine disease (MSUD) is a genetic disease caused by a deficiency of branched-chain keto acid dehydrogenase, a mitochondrial multienzyme complex responsible for the decarboxylation of leucine, isoleucine and valine. The complex consists of three subunits (E1, E2, and E3) and mutations in any subunit result in MSUD. No satisfactory treatment for MSUD is currently available. Here we report the successful use of retroviral gene transfer to restore leucine decarboxylation activity in fibroblasts derived from a MSUD patient containing a mutation in the E2 subunit. A full-length human E2 cDNA was inserted into a retroviral vector (MFG) and a stable CRIP producer line was generated. The amphotropic virus was then used to transduce mutant human fibroblasts. In untransduced mutant cells, 1-14C leucine decarboxylation activity was less than 2% that of the wild-type cells. Decarboxylation of 1-14C leucine in transduced mutant cells was restored to 93% of the wild-type level. Correct targeting of the expressed wild-type E2 protein to mitochondria was demonstrated by comparing the immunofluorescent pattern of E2 and a mitochondrial marker protein. Stable expression of enzyme activity has been obtained for at least 7 weeks. In contrast to most previous gene therapy attempts, which replace a single enzyme defect, the present results demonstrate complementation of a phenotype resulting from a gene defect whose product is a part of a multienzyme complex. Based on these results, studies can now be undertaken to investigate the feasibility of gene therapy to correct MSUD.

Amino Acid Oxidoreductases↗
PubMed1998

Pyruvate dehydrogenase complex deficiency and absence of subunit X.

The pyruvate dehydrogenase complex (PDHc) is a multienzyme complex consisting of three catalytic and two regulatory enzymes, as well as a less well defined subunit called protein X. PDHc deficiency is a common cause of congenital lactic acidosis. Most patients with PDH deficiency have a mutation in the alpha chain of the PDH E1 enzyme. Very few patients have been described in whom the basic defect of a PDH deficiency is situated in the X protein. We studied a boy with severe lactic acidosis and developmental delay in whom a deficiency of PDH activity led to further investigations. Immunochemical analysis with anti-PDHc antibodies demonstrated an absence of the X component. This report is the fourth family in which an abnormal protein X has been found. In cases with PDH deficiency where no mutation of the PDHE1 alpha gene is found, further investigations by means of immunoblotting with specific antibodies against the different subunits should be performed.

Female↗
PubMed1997

Biochemistry and autoimmune response to the 2-oxoacid dehydrogenase complexes in primary biliary cirrhosis.

Pyruvate dehydrogenase complex (PDC), 2-oxo-glutarate dehydrogenase complex (OGDC), and the branched-chain 2-oxoacid dehydrogenase complex (BCOADC) constitute the 2-oxoacid dehydrogenase family of multienzyme complexes. These complexes, which are larger than ribosomes and which consist of multiple copies of E1, E2, and E3 subunits together with regulatory kinases and phosphatases and, in the case of PDC, an E3-binding protein (protein X), each play an important role in oxidative metabolism in mitochondria. Primary biliary cirrhosis (PBC) is associated with a high incidence of autoantibodies directed at mitochondrial autoantigens (the antimito-chondrial antibodies), identified as the E2 components of PDC, OGDC, and BCOADC, together with protein X and the E1 alpha and E1 beta subunits of PDC. The dominant B-cell autoepitope in PBC has been identified as the inner lipoic acid binding domain of PDC-E2, with the lipoic acid co-factor, which plays a critical role in E2 enzymatic activity, playing a role in autoantibody binding to antigen. Autoreactive CD4+ T cells specific for human PDC-E2 are also present in both the peripheral blood and liver mononuclear cell infiltrates of PBC patients. The mechanism of break-down of B-cell and T-cell self-tolerance to these ubiquitous mitochondrial antigens in such an organ-specific manner remains unclear. The apparent importance of autoreactive responses to these self-antigens does, however, raise the possibility that antigen-specific immunotherapy may offer a novel route to therapy in PBC.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1998

Kinetics and specificity of reductive acylation of wild-type and mutated lipoyl domains of 2-oxo-acid dehydrogenase complexes from Azotobacter vinelandii.

The kinetics and specificity of reductive acylation of lipoyl domains derived from Azotobacter vinelandii 2-oxo-acid dehydrogenase complexes, catalysed by A. vinelandii and Escherichia coli complexes, have been investigated. With the wild-type pyruvate dehydrogenase complex from A. vinelandii the rate of reductive acetylation and deacetylation was studied by rapid mixing methods. The rate of reductive acetylation, 126 s(-1), corresponds well with the turnover rate derived from steady-state measurements. Deacetylation was rapid and specific for coenzyme A. No deacetylation was observed with reduced or oxidised lipoamide or with dithiothreitol. The rate of reductive acetylation of complex-bound lipoyl domains by pyruvate dehydrogenase (E1p) is at least 60 times higher than of free lipoyl domains under comparable conditions. This gain in catalytic rate indicates a large diffusion limitation of lipoyl domains when attached via the flexible linker segments to the complex, and illustrates the efficiency of substrate channeling in the multienzyme complex. The 2-oxo-acid dehydrogenases exhibit specificity for lipoyl domains in the reductive acylation reaction. The A. vinelandii lipoyl domain derived from the pyruvate dehydrogenase complex is a good substrate for A. vinelandii E1p, but not for A. vinelandii 2-oxoglutarate dehydrogenase (E1o), and vice versa. The A. vinelandii lipoyl domain of the pyruvate dehydrogenase complex is also, although at a lower rate, reductively acetylated by E. coli E1p and reductively succinylated by E. coli E1o. Likewise, the A. vinelandii lipoyl domain derived from the 2-oxoglutarate dehydrogenase complex is recognised by E. coli E1o, but not by E. coli E1p. This suggests that common determinants of the lipoyl domains exist that are responsible for recognition by the E1 components. On the basis of the observed specificity and lipoyl domain sequences and structures, an exposed loop of the A. vinelandii 2-oxoglutarate dehydrogenase complex lipoyl domain was subjected to mutagenesis. Although the reductive acylation experiments of mutants of the lipoyl domain indicate the importance of this loop for recognition, it is probably not the single determinant for specificity.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1990

Molecular cloning, transcriptional characterization, and sequencing of cDNA encoding the H-protein of the mitochondrial glycine decarboxylase complex in peas.

The glycine decarboxylase multienzyme complex is located in the mitochondrial matrix and catalyzes a key reaction of the photorespiratory C-2 cycle of C3 plants. The cDNA encoding the smallest subunit, the 13,900-dalton H-protein, of the glycine decarboxylase complex from pea (Pisum sativum) leaves was cloned, identified, characterized, and sequenced. The 678-nucleotide sequence contained a 495-nucleotide open reading frame capable of encoding the 165-amino-acid H-protein precursor. The N terminus of this protein contains a 34-amino-acid sequence which does not appear in the mature protein. This presequence resembles the amphiphilic helices observed with mitochondrial leader sequences in yeast. The 131-amino-acid mature protein from peas shares substantial homology with the enzyme isolated from chicken liver. The abundance of the H-protein mRNA was about 5-fold greater in light-grown pea seedlings compared to dark-grown seedlings. The amount of H-protein transcript increased within 4 h after the plants were transferred to white light and continued to increase up to 24 h. The time course for the accumulation of the H-protein mRNA was similar to that for the mRNA of the small subunit of ribulose-1,5-bisphosphate carboxylase.

Amino Acid Oxidoreductases↗
PubMed1979

Disassembly and gross structure of particulate aminoacyl-tRNA synthetases from rat liver. Isolation and the structural relationship of synthetase complexes.

The major high molecular weight complex of aminoacyl-tRNA synthetases is purified about 1000-fold with 30% yield from rat liver. The synthetase complex sediments at 24 S with a molecular weight of 900,000 +/- 75,000 and contains aminoacylation activities for lysine, arginine, isoleucine, leucine, methionine, glutamine, glutamate, and proline. The 24 S synthetase complex dissociates into 21 S, 18 S, 13 S, 12 S, and 10 S complexes with specific enzymatic activities. Dissociation of the 24 S complex into active free synthetases is achieved by hydrophobic interaction chromatography. The disassembly of the synthetase complex is consistent with the structural model of a heterotypic multienzyme complex and suggests that the complex formation is due to the specific intermolecular interactions among the synthetases.

Amino Acyl-tRNA Synthetases↗
PubMed1973

The purification and regulatory properties of alpha-oxoglutarate dehydrogenase from Acineobacter iwoffi.

The alpha-oxoglutarate dehydrogenase multienzyme complex was purified from Acinetobacter lwoffi to a high degree of homogeneity as shown by gel electrophoresis and analytical ultracentrifugation. Sedimentation-velocity analyses gave s(20,w) values which increased with increasing protein concentration, suggesting dissociation of the complex in dilute solution. The maximum s(20,w) value thereby obtained and the value determined by active enzyme centrifugation were both in the range 28-29S. Electron micrographs of the complex indicated a molecular diameter of 20-22nm (200-220A). The overall activity of the complex was inhibited by NADH, and kinetic studies indicated sites of action on the first and third enzyme components. AMP and ADP relieved this inhibition and also stimulated enzyme activity. Assays specific for the first enzyme component showed this to be the site of action of the adenylates. The activity of the complex varied with energy charge in a manner consistent with its role in energy metabolism.

Adenine Nucleotides↗
PubMed1998

Import rate of the E1beta subunit of human branched chain alpha-ketoacid dehydrogenase is a limiting factor in the amount of complex formed in the mitochondria.

Components of the mitochondrial branched chain alpha-ketoacid dehydrogenase multienzyme complex are all encoded by nuclear genes. The functional complex is formed with a known stoichiometric relationship of subunits, but how they enter the mitochondria and form the complex is not defined. Although cytosolic precursors for several of the proteins have been identified, the requirements for import and processing have not been described. Here we demonstrate the similar requirements for in vitro import and processing of the three catalytic subunits unique the this complex. Import was not affected by the amount of endogenous BCKD within the mitochondria. No cooperativity or competition among the subunits for import was found when subunits were used in combination. The relative rates of entry are E1alpha>E2>/=E1beta, making E1beta the limiting component supporting previously reported observations.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗