Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.5.3 (complex I)
 8,901 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The steady-state kinetics of the NADH dehydrogenase activity of the three-subunit flavo-iron-sulfur protein (FP, Type II NADH dehydrogenase) in the presence of the one-electron acceptor hexammineruthenium(III) (HAR) were studied. The maximal catalytic activities of FP with HAR as electron acceptor calculated on the basis of FMN content were found to be approximately the same for the submitochondrial particles, Complex I and purified FP. This result shows that the protein structure responsible for the primary NADH oxidation by FP is not altered during the isolation procedure and the lower (compared with Complex I) catalytic capacity of the enzyme previously reported was due to the use of inefficient electron acceptors. Simple assay procedures for NADH dehydrogenase activity with HAR as the electron acceptor are described. The maximal activity at saturating concentrations of HAR was insensitive to added guanidine, whereas at fixed concentration of the electron acceptor, guanidine stimulated oxidation of low concentrations of NADH and inhibited the reaction at saturating NADH. The inhibitory effect of guanidine was competitive with HAR. The double-reciprocal plots 1/v vs. 1/[NADH] at various HAR concentrations gave a series of straight lines intercepting on the ordinate. The plots 1/v vs. 1/[HAR] at various NADH concentrations gave a series of straight lines intercepting in the fourth quadrant. The kinetics support the mechanism of the overall reaction where NADH is oxidized by the protein-Ru(NH3)3+(6) complex in which positively charged electron acceptor is bound at the specific site close to FMN, thus stabilizing the flavosemiquinone intermediate.
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PMID:Kinetics of the mitochondrial three-subunit NADH dehydrogenase interaction with hexammineruthenium(III). 761 40

LHON (Leber hereditary optic neuropathy) is a maternally inherited disease that leads to sudden loss of central vision at a young age. There are three common primary LHON mutations, occurring at positions 3460, 11778 and 14484 in the human mtDNA (mitochondrial DNA), leading to amino acid substitutions in mitochondrial complex I subunits ND1, ND4 and ND6 respectively. We have now examined the effects of ND6 mutations on the function of complex I using the homologous NuoJ subunit of Escherichia coli NDH-1 (NADH:quinone oxidoreductase) as a model system. The assembly level of the NDH-1 mutants was assessed using electron transfer from deamino-NADH to the 'shortcut' electron acceptor HAR (hexammine ruthenium), whereas ubiquinone reductase activity was determined using DB (decylubiquinone) as a substrate. Mutant growth in minimal medium with malate as the main carbon source was used for initial screening of the efficiency of energy conservation by NDH-1. The results indicated that NuoJ-M64V, the equivalent of the common LHON mutation in ND6, had a mild effect on E. coli NDH-1 activity, while nearby mutations, particularly NuoJ-Y59F, NuoJ-V65G and NuoJ-M72V, severely impaired the DB reduction rate and cell growth on malate. NuoJ-Met64 and NuoJ-Met72 position mutants lowered the affinity of NDH-1 for DB and explicit C-type inhibitors, whereas NuoJ-Y59C displayed substrate inhibition by oxidized DB. The results are compatible with the notion that the ND6 subunit delineates the binding cavity of ubiquinone substrate, but does not directly take part in the catalytic reaction. How these changes in the enzyme's catalytic properties contribute to LHON pathogenesis is discussed.
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PMID:Leber hereditary optic neuropathy mutations in the ND6 subunit of mitochondrial complex I affect ubiquinone reduction kinetics in a bacterial model of the enzyme. 1789 48

A simple assay procedure for measuring ATP-dependent reverse electron transfer from ubiquinol to hexaammineruthenium (III) (HAR) catalyzed by mitochondrial respiratory complex I is introduced. The specific activity of the enzyme in this reaction and its sensitivity to the standard inhibitors and uncoupling are the same as with other well-known electron acceptors, NAD+ and ferricyanide. In contrast to the reactions with these acceptors, the energy-dependent HAR reduction is not inhibited by NADH-OH, the specific inhibitor of NADH-binding site. These results suggest that a catalytically competent electron connection exists between HAR and a redox component of complex I that is different from flavin mononucleotide bound at the substrate-binding site.
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PMID:FMN site-independent energy-linked reverse electron transfer in mitochondrial respiratory complex I. 2985 Oct 85