Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.99.3 (diaphorase)
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The genes that encode the two different subunits of the novel electron-transferring flavoprotein (ETF) from Megasphaera elsdenii were identified by screening a partial genomic DNA library with a probe that was generated by amplification of genomic sequences using the polymerase chain reaction. The cloned genes are arranged in tandem with the coding sequence for the beta-subunit in the position 5' to the alpha-subunit coding sequence. Amino acid sequence analysis of the two subunits revealed that there are two possible dinucleotide-binding sites on the alpha-subunit and one on the beta-subunit. Comparison of M. elsdenii ETF amino acid sequence to other ETFs and ETF-like proteins indicates that while homology occurs with the mitochondrial ETF and bacterial ETFs, the greatest similarity is with the putative ETFs from clostridia and with fixAB gene products from nitrogen-fixing bacteria. The recombinant ETF was isolated from extracts of Escherichia coli. It is a heterodimer with subunits identical in size to the native protein. The isolated enzyme contains approximately 1 mol of FAD, but like the native protein it binds additional flavin to give a total of about 2 mol of FAD/dimer. It serves as an electron donor to butyryl-CoA dehydrogenase, and it also has NADH dehydrogenase activity.
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PMID:Cloning and analysis of the genes for a novel electron-transferring flavoprotein from Megasphaera elsdenii. Expression and characterization of the recombinant protein. 969 53

Methanogenic oxidation of butyrate to acetate requires a tight cooperation between the syntrophically fermenting Syntrophomonas wolfei and the methanogen Methanospirillum hungatei, and a reversed electron transport system in S. wolfei was postulated to shift electrons from butyryl coenzyme A (butyryl-CoA) oxidation to the redox potential of NADH for H(2) generation. The metabolic activity of butyrate-oxidizing S. wolfei cells was measured via production of formazan and acetate from butyrate, with 2,3,5-triphenyltetrazolium chloride as electron acceptor. This activity was inhibited by trifluoperazine (TPZ), an antitubercular agent known to inhibit NADH:menaquinone oxidoreductase. In cell extracts of S. wolfei, the oxidation of NADH could be measured with quinones, viologens, and tetrazolium dyes as electron acceptors, and also this activity was inhibited by TPZ. The TPZ-sensitive NADH:acceptor oxidoreductase activity appeared to be membrane associated but could be dissociated from the membrane as a soluble protein and was semipurified by anion-exchange chromatography. Recovered proteins were identified by peptide mass fingerprinting, which indicated the presence of an NADH:acceptor oxidoreductase as part of a three-component [FeFe] hydrogenase complex and a selenocysteine-containing formate dehydrogenase. Furthermore, purification of butyryl-CoA dehydrogenase (Bcd) activity and peptide mass fingerprinting revealed two Bcd proteins different from the Bcd subunit of the Bcd/electron-transfer flavoprotein complex (Bcd/EtfAB) predicted from the genome sequence of S. wolfei. The results suggest that syntrophic oxidation of butyrate in S. wolfei involves a membrane-associated TPZ-sensitive NADH:acceptor oxidoreductase as part of a hydrogenase complex similar to the recently discovered "bifurcating" hydrogenase in Thermotoga maritima and butyryl-CoA dehydrogenases that are different from Bcd of the Bcd/EtfAB complex.
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PMID:Involvement of NADH:acceptor oxidoreductase and butyryl coenzyme A dehydrogenase in reversed electron transport during syntrophic butyrate oxidation by Syntrophomonas wolfei. 1964 44