2-oxoacid dehydrogenase complexes

BCOADC branched-chain 2-oxoacid 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...

Lawson, R. Cook, K.G. Yeaman, S.J. Rapid purification of bovine kidney branched-chain 2-oxoacid dehydrogenase complex containing endogenous kinase activity. FEBS Lett., 157, 54-58 (1982)... 

Within many tissues the enzymatic activities of the pyruvate and branched chain oxoacid dehydrogenases complexes are controlled in part by a phosphorylation -dephosphorylation mechanism (see Eq. 17-9). Phosphorylation of the decarboxylase subunit by an ATP-dependent kinase produces an inactive phosphoenzyme. A phosphatase reactivates the dehydrogenase to complete the regulatory cycle (see Eq. 17-9 and associated discussion). The regulation is apparently accomplished, in part, by controlling the affinity of the protein for... 

Oxoacid dehydrogenase complex http //qcg.tran.wau.nl/local/pdhc.htm... 

The absence in halobacteria of the oxoacid dehydrogenase complexes creates another puzzle. In most known systems, the role of the enzyme lipoamide dehydrogenase is to reoxidize the lipoic acid that is involved in the oxidation of the oxoacids in the oxoacid dehydrogenase complexes. This enzyme was nonetheless found in H. halobium and purified to homogeneity by Danson et al. (1986). What, then, is its function It is likely that lipoamide dehydrogenase assumes a different role in halobacteria. Another reducing system unique to... 

As reviewed previously [1], there are distinct mechanistic similarities between the archaebacterial oxidoreductases and the 2-oxoacid dehydrogenase complexes, despite their obvious structural differences. Thus, both systems form acyl-CoA via a TPP-... 

The mechanism suggested by Kerscher and Oesterhelt is indicated in Scheme 46 for the enzyme from H. halobium (213). The initial step is identical to that of the 2-oxoacid dehydrogenase complexes and involves binding of pyruvate to thiamin diphosphate and subsequent decarboxylation yielding hydroxyethylthia-min diphosphate. This intermediate undergoes one-electron transfer to the [4Fe-4S] cluster to form the stable free radical. The cluster is then reoxidized by ferredoxin or oxygen to give the enzyme-intermediate complex. Reaction with CoA initiates the second electron transfer to the iron-sulfur cluster, acyl transfer, followed by reoxidation of the enzyme by ferredoxin or O2 to complete the cycle. Two basic questions are yet unanswered (1) What is the mechanism of the enzymic reaction between CoASH and hydroxyethyl-TPP in the absence... 

The results so far indicate that the epitopes or binary interaction surfaces of E2ec for Elec and E3ec are certainly overlapping and suggest competition between Elec and E3ec for E2ec. The precise nature of these interactions still needs further delineation even in the simpler bacterial 2-oxoacid dehydrogenase complexes. 

Scheme 6 (a)Domain structure of the E2 component of the 2-oxoacid dehydrogenase complexes, (b) Schematic layout of domains in the 1-lipolyl E2ec. The lipoyl domain (LD) with the appended lipoamide visits the active sites of all three components of PDHc-ec. 

Figure 11.2 Reaction sequences catalyzed by 2-oxoacid dehydrogenase complex Pyruvate dehydrogenase complex (PDC) and a-ketoglutarate dehydrogenase complex (aKGDC) catalyze the oxidative decarboxylation of pyruvate (R = CH3) and a-ketoglutarate (R = CH2CH2COOH) to Acetyl-CoA and succinyl CoA respectively. Three component enzymes 2-oxoacid (pyruvate/a-ketoglutarate) decarboxylase, lipoate acetyltransferase/succinyltransferase, dihydrolipoate dehydrogenase as well as five cofactors, namely (1) thiamine pyrophosphate (TPP) and its acylated form, (2) lipoamide (LipS2), reduced form and acylated form, (3) flavin adenine dinucleotide (FAD) and its reduced form, (4) nicotinamide adenine dinucleotide (NAD ) and its reduced form, and (5) coenzyme A (CoASH) and its acylated product are involved.

Branched-chain-oxoacid dehydrogenase complex, which is responsible for the oxidative decarboxylation of the oxoacids derived from leucine, isoleucine and valine. Increased concentrations of all 3 branched chain amino acids and their oxoacids in urine, plasma and cerebrospinal fluid. Serum tilso contains alloiso-leucine (probably derived from isoleucine). Urine has characteristic odor. Marked cerebral degeneration apparently shortly after birth. Usually fatal within weeks or months of birth. 

Composition of the 2-oxoacid dehydrogenase complex of Escherichia coii... 

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