Precursor forms of the constituent polypeptides of pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase complexes from ox heart

Marcucci, Olga G. L. De; Hunter, Anne; Lindsay, J. Gordon

doi:10.1042/bst0140870

Cited by 5 publications

(3 citation statements)

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“…This portion of E3 could be involved in the interaction with the other component(s) of the a-ketoacid dehydrogenase complexes that are different in structure and symmetry between E. coli and mammals. Glutathione reductase, in accordance with previous comparisons (26), also shows a significant homology with E. coli E3 (28% homology) (35), pig heart E3 (partial) (40% homology) (27), and human liver E3 (33% homology) (present study). It is interesting to note that most of the homologies between glutathione reductase and both E. coli and human E3 are coincident with the ones between both E3 sequences.…”

Section: Discussionsupporting

confidence: 75%

“…When the molecular mass of a FAD molecule (Da = 703) is added, the total molecular mass comes to 50,919 daltons. This value is close to those obtained by sodium dodecyl sulfate electrophoresis, giving a subunit molecular mass of about 55,000 daltons (6,7,26). The calculated molecular mass of the leader sequence (4069) is larger than those obtained for rat heart (3000; ref.…”

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confidence: 60%

“…7) and ox heart (2000; ref. 26), although these data are based on differences between the precursor and the mature forms of E3. Only about 50% of the primary amino acid sequence of pig heart E3 has been determined (13,27).…”

mentioning

confidence: 99%

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Cloning and cDNA sequence of the dihydrolipoamide dehydrogenase component human alpha-ketoacid dehydrogenase complexes.

Pons

Raefsky-Estrin

Carothers

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

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ABSTRACTcDNA clones comprising the entire coding region for human dihydrolipoamide dehydrogenase (dihydrolipoamide:NAD+ oxidoreductase, EC 1.8.1.4) have been isolated from a human liver cDNA library. The cDNA sequence of the largest clone consisted of 2082 base pairs and contained a 1527-base open reading frame that encodes a precursor dihydrolipoamide dehydrogenase of 509 amino acid residues. The first 35-amino acid residues of the open reading frame probably correspond to a typical mitochondrial import leader sequence. The predicted amino acid sequence of the mature protein, starting at the residue number 36 of the open reading frame, is almost identical (>98% homology) with the known partial amino acid sequence of the pig heart dihydrolipoamide dehydrogenase. The cDNA clone also contains a 3' untranslated region of 505 bases with an unusual polyadenylylation signal (TATAAA) and a short poly(A) track. By blothybridization analysis with the cDNA as probe, two mRNAs, 2.2 and 2.4 kilobases in size, have been detected in human tissues and fibroblasts, whereas only one mRNA (2.4 kilobases) was detected in rat tissues.The a-ketoacid dehydrogenase complexes-the pyruvate dehydrogenase multienzyme complex, the a-ketoglutarate dehydrogenase multienzyme complex, and the branchedchain a-ketoacid dehydrogenase multienzyme complexcatalyze the oxidative decarboxylation of pyruvate, aketoglutarate, and the branched-chain a-ketoacids, respectively (1-4). These three complexes occupy key positions in energy metabolism and are involved (i) in connecting glycolysis with the Krebs cycle, (ii) in the Krebs cycle itself, and (iii) in the regulation of the oxidation of branched-chain amino acids, respectively. Each complex consists of at least three catalytic components. The decarboxylase component, which has been designated E1, is specific for each complex, and it most likely represents the rate-limiting step in the overall reaction. The dihydrolipoamide acyltransferase component, designated E2, also substrate specific, is involved in the transfer of the acyl group to CoA. The third component of each complex, dihydrolipoamide dehydrogenase (dihydrolipoamide:NAD+ oxidoreductase, EC 1.8.1.4), designated E3, is considered to be common to all three complexes. E3, a homodimer (subunit Mr = 55,000), contains a noncovalently bound molecule of FAD per subunit and catalyzes the reoxidation of the disulfhydryl form of the lipoyl residue bound to the E2 molecules of the complexes: E3 E2-Lip-(SH)2 + NAD+ <--E2-LiP(S)2 + NADH + H+ Three lines of evidence indicate that the E3 present in these three complexes is identical; they are reconstitution experiments (5), immunological cross-reactivity (6-9), and genetic disorders of E3, which cause simultaneous increases in the blood levels of pyruvate, a-ketoglutarate, and branched-chain ketoacids (10). The glycine cleavage system also contains a dihydrolipoamide dehydrogenase component known as L protein (11). However, this system has not been purified as an intact complex. We have recently suggested th...

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Section: Discussionsupporting

confidence: 75%

mentioning

confidence: 60%