Succinate:ubiquinone

Complex II (Succinate Dehydrogenase Succinate Ubiquinone Oxidoreductase)... 

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.

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. 

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 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... 

The Tte of the 3Fe-4S centre in succinate ubiquinone reductase between 4 and 8 K is decreased by interaction with paramagnetic cytochrome b.98 To mitigate the impact of spectral diffusion the relaxation times were measured by a picket-fence sequence with 100 pulses. Analysis of the powder pattern distribution of relaxation times indicated that the anisotropic dipolar interaction dominated over isotropic scalar interaction and a lower limit of 10 A was estimated for the distance between the iron-sulfur cluster and the heme. 

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. 

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... 

Two instructive examples of the use of phospholipid reagents are the labeling of succinate-ubiquinone reductase (complex II) (Girdlestone et al., 1981) and the labeling of glycophorin A (Ross et al., 1982). 

UQ may also be reduced by complex II (succinate ubiquinone oxido-reductase, succinate dehydrogenase), which contains four polypeptide chains, molecular weights 70,000, 27,000, 15,500, and 13,500. The first two constitute bona fide succinate dehydrogenase, a Krebs cycle enzyme catalyzing reaction... 

Figure 7-1. Pathways of fuel metabolism and oxidative phosphorylation. Pyruvate may be reduced to lactate in the cytoplasm or may be transported into the mitochondria for anabolic reactions, such as gluconeogenesis, or for oxidation to acetyl-CoA by the pyruvate dehydrogenase complex (PDC). Long-chain fatty acids are transported into mitochondria, where they undergo [ -oxidation to ketone bodies (liver) or to acetyl-CoA (liver and other tissues). Reducing equivalents (NADH, FADII2) are generated by reactions catalyzed by the PDC and the tricarboxylic acid (TCA) cycle and donate electrons (e ) that enter the respiratory chain at NADH ubiquinone oxidoreductase (Complex 0 or at succinate ubiquinone oxidoreductase (Complex ID- Cytochrome c oxidase (Complex IV) catalyzes the reduction of molecular oxygen to water, and ATP synthase (Complex V) generates ATP fromADP Reprinted with permission from Stacpoole et al. (1997).

It has been shown recently that the mitochondrial electron transport system contains at least three different fe-type cytochromes 178). Two of these cytochromes are found in complex III, and under appropriate conditions are reducible with substrates. The third 6-type cytochrome was discovered by Davis et al. 178), and shown to fractionate exclusively into complex II. At 77°K, the cytochrome 6 of complex II exhibits a double a band at 557.5 and 550 nm, a prominent band at 531 nm, and a Soret band at 422 nm (Fig. 29). Cytochrome 6557.5 appears to have a low reduction potential. It is not detectably reduced by succinate in either complex II or respiratory particles, but its dithionite reduced form is rapidly oxidized by either fumarate or ubiquinone. The role of this cytochrome in mammalian mitochondria is not known. Davis et al. 178) have suggested that it might be an electron entry point for an unknown ancillary tributary of the respiratory chain. Further, Bruni and Racker 179) have shown that a preparation of cytochrome 6 is required for reconstitution of succinate-ubiquinone reductase activity (see below). 

The second type of reconstitution is demonstrated by the work of Bruni and Racker (179). These investigators reconstituted a succinate-ubiquinone reductase system from a King-type preparation of succinate dehydrogenase (2.6 nmoles flavin per mg protein), a preparation of cytochrome b (24-27 nmoles heme per mg protein) solubilized and purified with the use of bile salts and SDS, and mitochondrial or soybean phospholipids. The highest succinate-ubiquinone reductase activity achieved was 980 moles succinate oxidized per minute per mole of succinate dehydrogenase flavin. While this activity is only 10% of the turnover number of complex II, it is still quite appreciable for this type of reconstitution. Since the preparations of succinate dehydrogenase and cytochrome b used were not pure, it is not known what is the minimum number of components needed for reconstitution of succinate-ubiquinone reductase activity. The role and the exact nature of the b-type cytochrome used in these experi-... 

Weiss, H., and Kolb, H. J., 1979, Isolation of mitochondrial succinate ubiquinone reductase, cytochrome c reductase and cytochrome c oxidase from Neurospora crassa using nonionic detergent, Eur. J. Biochem. 99 139nl49. 

The mitochondrial respiratory chain, which contains at least 13 Fe-S clusters (Figure 6), perhaps best illustrates the importance of Fe-S clusters in membrane-bound electron transport. Electrons enter via three principal pathways, from the oxidation of NADH to NAD+ (NADH-ubiquinone oxidoreductase or Complex I) and succinate to fumarate (succinate ubiquinone oxidoreductase or Complex II), and from the /3-oxidation of fatty acids via the electron transferring flavoprotein (ETF-ubiquinone oxidoreductase). All three pathways involve a complex Fe S flavoprotein dehydrogenase, that is, NADH dehydrogenase, succinate dehydrogenase, and ETF dehydrogenase, and in each case the Fe-S clusters mediate electron transfer from the flavin active site to the ubiquinone pool via protein-associated ubiquinone. 

Complex II is usually measured in two ways either as succinate ubiquinone oxidoreductase or as succinate cytochrome c oxidoreductase. The most commonly used assay for succinate ubiquinone oxidoreductase (or isolated complex II) uses DCIP in the same way as described above for the new complex I assay, only in this case succinate is added as a substrate (instead of NADH). The specificity of DCIP reduction can be determined by measuring in the presence or absence of mal-onate, a specific inhibitor of complex II. The assay for succinate cytochrome c oxidoreductase (or complex II 4- HI) uses succinate and oxidized cytochrome c as substrates and measures the reduction of cytochrome c, which can be followed spectrophotometrically at 550 nm. The assay is also suitable to screen for coenzyme Q deficiencies, as it is dependent on the endogenously present CoQio- In case of a CoQ deficiency, a reduced succinate cytochrome c oxidoreductase activity will be... 

Fig. 22. Resolution of complex II with respect to succinate dehydrogenase by various chaotropes. Complex II was suspended in 50 mAf Tris-HCl, pH 8.0. After addition of 0.6 M chaotrope the concentration of complex II was 8 mg/ml. After addition of the salts, samples were taken at the intervals indicated and assayed for succinate-Qj and succinate-PMS reductase activities. Solid lines, succinate-ubiquinone-2(Q) reductase activity dotted line, succinate-PMS reductase activity. Resolution temperature, 0° assay temperature, 38°. The complex II preparations used in the experiments of this and subsequent Figs. 24 and 25 had specific activities between 40 and 45 iimoles Qi reduced by succinate per min per mg protein. From Davis and Hatefi (159).

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