The NADH-ubiquinone reductase complex

NADH-ubiquinone reductase (EC 1.6.5.3) or Complex I is structurally by far the most complicated member of the respiratory chain. It is also the least known in terms of structure, electron transfer pathway or mechanism of proton translocation. Even the nomenclature of the isolated enzyme entities and of the FeS centres is problematic because it differs between research groups. 

Complex I is the lipid-containing isolated preparation, with properties (Table 3.7) [39] that best correspond to the Site 1 region of the respiratory chain of intact mitochondria. 

Contains FMN, nonhaem Fe, acid- abile sulphur, ubiquinone-10 and lipids (Table 3.8). The several constituent polypeptides probably include ubiquinone-binding proteins (281). 

Catalyses rapid rotenone-sensitive reduction of Q-1 by NADH. 

Catalyses rapid NADH-linked reduction of ferricyanide, but reacts slowly with other acceptors. 

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PG is made in mitochondria and microsomes of animal cells and appears to be primarily converted to DPG. DPG is biosynthesized exclusively on the matrix side of the mitochondrial inner membrane and is found only in this organelle. There is evidence that the rate-limiting step in DPG biosynthesis is the conversion of PA into CDP-DG (G.M. Hatch, 1994). Consistent with this idea, the levels of CTP regulate DPG biosynthesis in cardiac myoblasts (G.M. Hatch, 1996). Using techniques developed by Raetz and co-workers [14], a temperature-sensitive mutant of PG-P synthase in CHO cells was isolated (M. Nishijima 1993). The mutant had only 1% of wild-type PG-P synthase activity at 40°C and exhibited a temperature-sensitive defect in PG and DPG biosynthesis. This mutant was used to show that DPG is required for the NADH-ubiquinone reductase (complex I) activity of the respiratory chain. 

Thus, by combining the NADH-ubiquinone reductase complex with a heterogeneous fraction solubilized from bovine heart submitochondrial fractions (referred to as hydrophobic protein ) and phospholipids (phosphatidylethanolamine, phosphatidylcholine, cardiolipid), Ragan and Racker and his associates [146] were able to reconstitute vesicles. These vesicles, which can be isolated on sucrose gradients, carry on the phosphorylation of ADP to ATP, and the oxidative phosphorylation is sensitive to uncouplers. 

Piericidins are the first compounds obtained by the screening search for insecticidal natural products among microbial metabolites.10 They were isolated from Streptomyces mobaraensis in 1963,11 and many piericidin derivatives have been found in microbial metabolites until now.12 Piericidins are not used as insecticides practically, but are important biological reagents because they have specific inhibitory activity toward the mitochondrial electron transport chain protein nicotinamide adenine dinucleotide (NADH)-ubiquinone reductase (complex I).13 Piericidin Ax (1 in Figure 1) is biosynthesized as a polyketide,14 but genes responsible for its biosynthesis are not yet identified. Total synthesis of piericidins A (1) was reported recently.15... 

In benzoquinone-treated algae, the re-reduction rate of Cyt c could be accelerated by increasing the concentration of reduced DAD (not shown). In this case, addition of myxothiazol also blocked the reaction. Therefore, the inhibition caused by the treatment is not due to its impairing the b-c complex, but rather affects an upstream step, such as ubiquinone reduction. This was actually verified by Prof. R. Douce (personal communication), who found that p-benzoquinone was an inhibitor of the NADH-ubiquinone- reductase in isolated plant mitochondria. The slow re-reduction of Cyt c in Fig. 1 depends on the duration and concentration of the benzoquinone treatment, and as mentioned above, on the added reductant. In this experiment sufficient reduction occurs within each flashing period so that the saturation effect observed in the myxothiazol curve of Fig.2 does not occur. As shown in [l], under such conditions, the mitochondrial response remains linear. 

Schmidt M, Wallrath J, Dorner A, Weiss H. Disturbed assemble of the respiratory chain NADH ubiquinone reductase (complex I) in citric-acid-accumulating Aspergillus niger strain B 60. Appl Microbiol Biotechnol 1992 36 667-72. 

The respiratory chain can be separated by various techniques into three multienzyme complexes (Figure 16.3). Complex I is NADH-ubiquinone reductase. Complex III is known as ubiquinone-cytochrome c reductase and contains cytochromes b and Ci. Complex IV is cytochrome oxidase. (Succinate dehydrogenase is referred to as Complex II). Ubiquinone and cytochrome c are small molecules which do not form part of these complexes. Reconstitution of the isolated Complexes I-IV with cytochrome c and ubiquinone leads to recovery of the activity of the respiratory chain. 

NADH-ubiquinone reductase) and the second one was complex II (succinate-ubiquinone reductase). Chiesi and Schwaller [101] found that quercetin and tannin inhibited neuronal constitutive endothelial NO synthase. 

In the hydrogenosomal membranes, EPR spectra showed no trace of the highly characteristic features of the iron-sulfur clusters of complex I (NADH ubiquinone reductase) and the Rieske protein of complex III of the mitochondrial respiratory chain. This is consistent with the absence of... 

Friedrich, T., VanHeek, P., Leif, H., Ohnishi, T., Forche, E., Kunze, B., Jansen, R., Trowitzsch-Kienast, W., Holfe, G., Reichenbach, H., and Weiss, H. Two binding sites of inhibitors in NADH ubiquinone oxidoreductase (complex I) relationship of one site with the ubiquinone oxido-reductase. Eur. J. Biochem., 219, 691, 1994. 

Preparations of NADH dehydrogenase from mammalian mitochondria may be divided into three types (1) NADH-ubiquinone reductase or complex I of the electron transport system, (2) the high molecular weight NADH dehydrogenases, and (3) the low molecular weight NADH dehy-... 

NADH-ubiquinone reductase was isolated by Hatefi et al. in 1961 (27-B9). A procedure was developed for the resolution of the mitochondrial electron transport system into four enzyme complexes. Recently, a fifth fraction, which is capable of energy conservation and ATP-Pi exchange, was also isolated (30, 31). The overall scheme for the isolation of the five component enzyme complexes of the mitochondrial electron transport-oxidative phosphorylation system is given in Fig. 1. It is seen... 

The ubiquinone reductase activity of their low molecular weight dehydrogenase led Pharo et al. (64, 75) to conclude that the enzyme represented the mitochondrial NADH-ubiquinone reductase. However, it has been shown that the quinone reductase activity of the low molecular weight dehydrogenase is different from that of intact respiratory particles or complex I in many important respects, including kinetic constants, re-... 

The electron carriers in the respiratory assembly of the inner mitochondrial membrane are quinones, flavins, iron-sulfur complexes, heme groups of cytochromes, and copper ions. Electrons from NADH are transferred to the FMN prosthetic group of NADH-Q oxidoreductase (Complex I), the first of four complexes. This oxidoreductase also contains Fe-S centers. The electrons emerge in QH2, the reduced form of ubiquinone (Q). The citric acid cycle enzyme succinate dehydrogenase is a component of the succinate-Q reductase complex (Complex II), which donates electrons from FADH2 to Q to form QH2.This highly mobile hydrophobic carrier transfers its electrons to Q-cytochrome c oxidoreductase (Complex III), a complex that contains cytochromes h and c j and an Fe-S center. This complex reduces cytochrome c, a water-soluble peripheral membrane protein. Cytochrome c, like Q, is a mobile carrier of electrons, which it then transfers to cytochrome c oxidase (Complex IV). This complex contains cytochromes a and a 3 and three copper ions. A heme iron ion and a copper ion in this oxidase transfer electrons to O2, the ultimate acceptor, to form H2O. 

Ubiquinone accepts electrons from NADH in a reaction in the respiratory electron transport chain catalyzed by the mitochondrial en mie complex NADH ubiquinone reductase. This enzyme complex in the yeast Pichiapastoris contains 41 polypeptide chains. 

NADH dehydrogenase (ubiquinone) [EC 1.6.5.3] (also called ubiquinone reductase, type I dehydrogenase, and complex I dehydrogenase) catalyzes the reaction of NADH with ubiquinone to produce NAD and ubiqui-nol. The complex, which uses EAD and iron-sulfur proteins as cofactors, is found in mitochondrial membranes and can be degraded to form NADH dehydrogenase [EC... 

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