Succinate-ubiquinone oxidoreductase

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. 

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... 

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... 

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).

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... 

The mitochondrial respiratory chain is composed of more than 80 proteins grouped into 5 distinct complexes that form an integrated electron transfer chain (ETC, Figure 4). Initiation of electron transport takes place either from complex I (reduced nicotinamide adenine diphosphate (NADH)—ubiquinone oxidor-eductase) or from complex II (succinate—ubiquinone oxidoreductase) to complex III (ubiquinol—cytochrome c oxidoreductase) by ubiquinone (UQ, coenzyme Q, 39). As shown in Scheme 1, ubiquinone is reduced to... 

In metazoans, the electron transport chain consists of four integral membrane complexes localized to the inner mitochondrial membrane complex I (NADH-ubiquinone oxidoreductase), complex II (succinate-ubiquinone oxidoreductase), complex III (ubiquinol-cytochrome c oxidoreductase) and complex IV (cytochrome c oxidase), plus coenzyme Q (ubiquinone) and cytochrome c. As first shown by Fry and Beesley (1991), the plasmodial electron transport chain differs from the metazoan system in lacking complex I however, a single subunit NADH dehydrogenase is present and is homologous to that found in plants, bacteria and yeast but not in animals (Krungkrai, 2004 Vaidya, 2004,2005 van Dooren et al., 2006). 

Trinuclear clusters have been detected in over 20 proteins as well as a number of enzymes, among them aconitase, beef heart succinate-ubiquinone oxidoreductase (120), Escherichia coli nitrate reductase (121), E. coli fumarate reductase (122), and succinate dehydrogenase (123). Selected instances of the occurrence of [3Fe-4S] clusters are listed in Table II. Because of the paramagnetic ground states of both oxidation levels, these clusters can be uniquely identified by a number of spectroscopic techniques. Among these, Mossbauer spectroscopy in applied magnetic fields (124, 128, 132, 141-143) and low temperature MCD spectroscopy (127, 138, 144-146) are decisive. While there are small spectroscopic differences among certain [3Fe-4S] centers, the similarities dominate and support the essential structure 3 for all. In a number of the earlier papers on protein... 

Mitochondria were extracted from mycelia of Rhizoctonia solani, Botrytis cinerea, and Fusarium oxysporum. Succinate-ubiquinone oxidoreductase activity was assayed spectrophotometrically following the method of Miyoshi [3] and the results are listed in Table 3 expressed as Ijq (50% inhibition). 

When mitochondria from bovine heart were solubilized by treatment with mild detergents it was possible to separate and purify the sections of the respiratory chain referred to earlier as coupling sites 1, 2 and 3. These were named Complex I (NADH-ubiquinone oxidoreductase), Complex III (ubiquinol-cytochrome c ox-idoreductase, cytochrome bci complex) and Complex IV (cytochrome c oxidase) [17], and have since been characterized as independent entities, although it is now recognized that these three complexes co-assemble with specific stoichiometry to form respiratory chain supercomplexes or respirasomes in fungal, plant and mammalian mitochondria [18-20]. There is also evidence that succinate-ubiquinone oxidoreductase (which was purified alongside the other complexes and named Complex II [21]) forms a tight association with Complex III in yeast mitochondria [22]. 

Figure 8.8. Stereo view of E. coli succinate ubiquinone oxidoreductase, which is an analogue of Complex II of the electron transport chain of mitochondria, with neutral residues light gray, aromatics black, other hydrophobics gray, and charged residues white. (A) Space-filling representation with water...

Figure 8.11. Stereo view of Wolinella succinogenes fumarate reductase dimer, an analogue of mitochondrial succinate ubiquinone oxidoreductase (Complex II) of the electron transport chain. (A) Ligands in ball and stick representation and waters of Thales shown as light dots. (B) Ligands in space-...

Figure 1 shows the complex ESR spectra from isolated cardiac mitochondria. They appear as a superposition of spectra from various paramagnetic components of the mitochondrial ETC. They are mainly iron-sulfur centers, denoted as Nl, N2, N3 - - 4 (located in complex I, NADFi-ubiquinone oxidoreductase), SI (complex II, succinate-ubiquinone oxidoreductase), and the Rieske iron-sulfur protein (complex III, ubihydroquinone-cytochrome C oxidoreductase). The positions of the components... 

Although some of the available riboflavin in natural foods may be present as the free vitamin, ready for intestinal transport, a larger fraction is present in the form of phosphorylated coenzymes FMN and flavin adenine dinucleotide (FAD), and there may also be very small amoimts of a gluco-side of the vitamin. These forms are all efficiently converted to free vitamin by enzymes secreted into the gut lumen, and they are therefore highly available for absorption. There are also small amounts of covalently bound forms of riboflavin, present in enzymes such as succinate dehydrogenase (succinate ubiquinone oxidoreductase EC 1.3.5.1), which cannot be released by the hydrolytic enzymes in the gut and are therefore unavailable for absorption. Also unavailable (or very poorly available) in man is the riboflavin synthesized by the gut flora of the large bowel. Certain animal species such as rodents can utilize this riboflavin source by coprophagy. 

---