Ubiquinone Oxidoreductases

Electrons from NADH, together with two protons, are transferred to ubiquinone to form ubiquinol by complex I (NADH ubiquinone oxidoreductase). Complex I... 

Complexes of the Mitochondrial Electron-Transport Chain Complex I (NADH Ubiquinone Oxidoreductase)... 

Another pathway is the L-glycerol 3-phosphate shuttle (Figure 11). Cytosolic dihydroxyacetone phosphate is reduced by NADFl to s.n-glycerol 3-phosphate, catalyzed by s,n-glycerol 3-phosphate dehydrogenase, and this is then oxidized by s,n-glycerol 3-phosphate ubiquinone oxidoreductase to dihydroxyacetone phosphate, which is a flavoprotein on the outer surface of the inner membrane. By this route electrons enter the respiratory chain.from cytosolic NADH at the level of complex III. Less well defined is the possibility that cytosolic NADH is oxidized by cytochrome bs reductase in the outer mitochondrial membrane and that electrons are transferred via cytochrome b5 in the endoplasmic reticulum to the respiratory chain at the level of cytochrome c (Fischer et al., 1985). 

Figure 12-7. Proposed sites of inhibition (0) of the respiratory chain by specific drugs, chemicals, and antibiotics. The sites that appear to support phosphorylation are indicated. BAL, dimercaprol. TTFA, an Fe-chelating agent. Complex I, NADHiubiquinone oxidoreductase complex II, succinate ubiquinone oxidoreductase complex III, ubiquinohferricytochrome c oxidoreductase complex IV, ferrocytochrome ctoxygen oxidoreductase. Other abbreviations as in Figure 12-4.

Barker CD, Reda T, Hirst J. 2007. The flavoprotein suhcomplex of complex I (NADH ubiquinone oxidoreductase) from bovine heart mitochondria Insights into the mechanisms of NADH oxidation and NAD reduction from protein film voltammetry. Biochemistry 46 3454-3464. 

Saruta, F., Kuramochi, T., Nakamura, K, Takamiya, S., Yu, Y., Aoki, T., Sekimizu, K., Kojima, S. and Kita, K. (1995) Stage-specific isoforms of complex II (succinate-ubiquinone oxidoreductase) in mitochondria from the parasitic nematode, Ascaris suum. Journal of Biological Chemistry 270, 928-932. 

In the mitochondria, ONOO- can mediate damage to OXPHOS by nitrosylat-ing/oxidizing tyrosine or thiol functional groups, rendering catalytic inactivation of complex I [NADH ubiquinone oxidoreductase], complex II [succinate ubiquinone oxidoreductase] and complex V (FI, FO-ATPase), thereby impeding ETC/ OXPHOS... 

Qrunones can accept one or two electrons to form the semiquinone anion (Q ") and the hydroquinone dianion (Q ). Single-electron reduction of a quinone is catalyzed by flavoenzymes with relatively low substrate selectivity (Kappus, 1986), for instance NADPH cytochrome P-450 reductase (E.C. 1.6.2.3), NADPH cytochrome b5 reductase (E.C. 1.6.2.2), and NADPH ubiquinone oxidoreductase (E.C. 1.6.5.3). The rate of reduction depends on several interrelated chemical properties of a quinone, including the single-electron reduction potential, as well as the number, position, and chemical characteristics of the substituent(s). The flavoenzyme DT-diphorase (NAD(P)H quinone acceptor oxidoreductase E.C. 1.6.99.2) catalyzes the two-electron reduction of a quinone to a hydroquinone. 

Albracht SPJ, Hedderich R. 2000. Learning from hydrogenases location of a proton pump and of a second FMN in bovine NADH ubiquinone oxidoreductase (complex I) FEBS Lett 485 1-6. 

H. Ueno, H. Miyoshi, M. Inoue, Y. Niidome, H. Iwamura, Structural factors of rotenone required for inhibition of various NADH-ubiquinone oxidoreductases, Biochim. Biophys. Acta 1276 (1996) 195-202. 

In NADH-ubiquinone oxidoreductase, there are several sites for ubiquinone binding, and the semiquinone relaxation times are different at these sites.99Analysis of P1/2 of the CW power saturation curve for the fastest relaxing semiquinone signal, SQnf, gave a distance of 11 A between the semiquinone and iron-sulfur cluster N2. 

Gabaldon T, Rainey D, Huynen MA (2005) Tracing the evolution of a large protein complex in the eukaryotes, NADH ubiquinone oxidoreductase (complex I). J Mol Biol 348 857-870... 

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. 

FIGURE 19-9 IMADH ubiquinone oxidoreductase (Complex I). Complex I catalyzes the transfer of a hydride ion from NADH to FMN, from which two electrons pass through a series of Fe-S centers to the iron-sulfur protein N-2 in the matrix arm of the complex. Electron transfer from N-2 to ubiquinone on the membrane arm forms QH2, which diffuses into the lipid bilayer. This electron transfer also drives the expulsion from the matrix of four protons per pair of electrons. The detailed mechanism that couples electron and proton transfer in Complex I is not yet known, but probably involves a Q cycle similar to that in Complex III in which QH2 participates twice per electron pair (see Fig. 19-12). Proton flux produces an electrochemical potential across the inner mitochondrial membrane (N side negative, P side positive), which conserves some of the energy released by the electron-transfer reactions. This electrochemical potential drives ATP synthesis. 

Brandt, U. (1997) Proton-translocation by membrane-bound NADH ubiquinone-oxidoreductase (complex I) through redoxgated ligand conduction. Biochim Biophys. Acta 1318, 79-91. Advanced discussion of models for electron movement through Complex I. 

NADH-methemoglobin reductase 826 NADH ubiquinone oxidoreductase 788 oxidation by ferricyanide 780 NADP+ (NADP) 507, 765 - 771, 767s, 779 in catalase 853 isolation of 767... 

These complexes are usually named as follows I, NADH-ubiquinone oxidoreductase II, succinate-ubiquinone oxidoreductase III, ubiquinol-cytochrome c oxidoreductase IV, cytochrome c oxidase. The designation complex V is sometimes applied to ATP synthase (Fig. 18-14). Chemical analysis of the electron transport complexes verified the probable location of some components in the intact chain. For example, a high iron content was found in both complexes I and II and copper in complex IV. 

Figure 18-7 Three-dimensional image of bovine NADH-Ubiquinone oxidoreductase (complex I) reconstructed from individual images obtained by electron cyro-microscopy.

Hydrogenase (D. desulfuricans) Succinate-ubiquinone oxidoreductase (complex II) Aconitase (inactive) 83 000 0... 

The study of such magnetic field dependence of the LEFE in ESR spectroscopy has allowed the demonstration that the iron-sulfur cluster in beef heart succinate-ubiquinone oxidoreductase is a 3Fe cluster.815... 

Engler M, Anke T, Sterner O, Brandt U (1997) Pterulinic Acid and Pterulone, Two Novel Inhibitors of NADH Ubiquinone Oxidoreductase (Complex I) Produced by a Pterula Species I. Production, Isolation and Biological Activities. J Antibiot 50 325... 

T Yagi, Y Hatefi. Identification of the dicyclohexylcarbodiimide-binding subunit of NADH-ubiquinone oxidoreductase (Complex I). J Biol Chem 263 16150-16155, 1988. 

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