Complex succinate-dehydrogenase

Flutolanil is an inhibitor of succinate dehydrogenase complex (Complex II), in the mitochondrial respiratory electron transport chain. ... 

Complex II. The succinate dehydrogenase complex, or complex IF, contains a non-haem iron-sulfur component and utilises the electron acceptor FAD to effect the transfer of electrons from FADH2 to coenzyme Q. Inhibitors of succinate dehydrogenase are specific basidio-mycete fungicides, with uses against smuts, bunts, and Rhizoctonia spp. (Figure 4.21). 

Some electrons enter this chain of carriers through alternative paths. Succinate is oxidized by succinate dehydrogenase (Complex II), which contains a flavoprotein that passes electrons through several Fe-S centers to ubiquinone. Electrons derived from the oxidation of fatty acids pass to ubiquinone via the electron-transferring flavoprotein. 

Complex II The Succinate Dehydrogenase Complex. Succinate dehydrogenase is the only enzyme of the TCA cycle that is embedded in the inner membrane. Its four subunits include two iron-sulfur proteins, one of which also has a covalently attached FAD. As in NADH dehydrogenase, the substrate-oxidation site is on the matrix side of the membrane (fig. 14.10). 

Effects of Mutations in Mitochondrial Complex II Single nucleotide changes in the gene for succinate dehydrogenase (Complex II) are associated with midgut carcinoid tumors. Suggest a mechanism to explain this observation. 

Figure 7.27 The electron transport chain showing the three phosphorylation sites and points where insecticides inhibit this process. Flavoprotein represents complex I (NADH dehydrogenase). Coenzyme Q also accepts electrons from succinate dehydrogenase (complex II). Cytochrome b represents complex III consisting of cytochrome bc complex. Cytochrome oxidase represents complex IV.

As indicated in Sections 1 and 2, succinate is an electron donor widely utilized for NAD(P) reduction by phototrophic purple bacteria. The membrane-bound enzyme responsible for succinate oxidation has been solubilized and partially characterized in the purple non-sulfur bacteria R. rubrum [73,74] and Rhodopseudo-monas sphaeroides (recently renamed Rhodobacter sphaeroides) [57]. In situ characterization of the iron-sulfur centers likely to be associated with succinate dehydrogenase has been accomplished for Rps. capsulata [59] and C. vinosum [51]. Of particular interest is the presence of a succinate-reducible [51,57,58,73] and fu-marate-oxidizable [51] iron-sulfur cluster with near +50 mV that, like center S-3 [60,61,75,76] of mitochondrial succinic dehydrogenase (Complex II), is paramagnetic in the oxidized state. The enzyme in phototrophic bacteria also appears to have one or two ferredoxin-like (i.e., paramagnetic in the reduced state) iron-sulfur centers that correspond to centers S-1 (succinate-reducible, EJ ranging from... 

Fig. 3.1. A, The respiratory chain. Q and c stand for ubiquinone and cytochrome c, respectively. Auxiliary enzymes that reduce ubiquinone include succinate dehydrogenase (Complex II), a-glycerophosphate dehydrogenase and the electron-transferring flavoprotein (ETF) of fatty acid oxidation. Auxiliary enzymes that reduce cytochrome c include sulphite oxidase. B, Thermodynamic view of the respiratory chain in the resting state (State 4). Approximate values are calculated according to the Nernst equation using oxidoreduction states from work by Muraoka and Slater, (NAD, Q, cytochromes c c, and a oxidation of succinate [6]), and Wilson and Erecinska (b-562 and b-566 [7]). The NAD, Q, cytochrome b-562 and oxygen/water couples are assumed to equilibrate protonically with the M phase at pH 8 [7,8]. E j (A ,/ApH) for NAD, Q, 6-562, and oxygen/water are taken as —320 mV ( — 30 mV/pH), 66 mV (- 60 mV/pH), 40 mV (- 60 mV/pH), and 800 mV (- 60 mV/pH) [7-10]. FMN and the FeS centres of Complex I (except N-2) are assumed to be in redox equilibrium with the NAD/NADH couple, FeS(N-2) with ubiquinone [11], and cytochrome c, and the Rieske FeS centre with cytochrome c [10]. The position of cytochrome a in the figure stems from its redox state [6] and its apparent effective E -, 285 mV in...

Abbreviations FAD, flavin adenine dinucleotide Fe-S, iron-sulfur proteins that can he identified in separate clusters by electron paramagnetic resonance analysis (the s-1, s-2 subscripts identify these iron-sulfur proteins as part of the succinate dehydrogenase complex) His, the histidine linkage between FAD and the large (70,000 daltons) protein moiety of the enzyme FMN, flavin mononucleotide N-la, N-2 subscripts identify these iron-sulfur proteins as part of the NADH-dehydro-genase complex UQ, ubiquinone Cyt bf and Cyt b, cytochrome b-566 and b-563, respectively. 

Fig. 6. Electron transport in plants and fimgi. Three complexes (7, II and IV) translocate protons to gradient across the mitochondrial membrane Complex 7NADH dehydrogenase complex II succinate dehydrogenase complex III cytochrom be, complex IV cytochrome c oxidase (Cox). Cyc Cytochrome c UbiQ ubiquinone Aox alternative oxidase SHAM salicylhy-droxamic acid AA antimycin A KCN potassimn cyanide. (From Vanlerberghe and McIntosh [137])...

The succinate dehydrogenase complex (complex II) consists primarily of the citric acid cycle enzyme succinate dehydrogenase and two iron-sulfur proteins. Complex II mediates the transfer of electrons from succinate to UQ. The... 

I. Thus when electrons enter the alternative respiratory pathway through the rotenone-insensitive NADH dehydrogenase, the external NADH dehydrogenase, or succinate dehydrogenase (Complex II), and pass to O2 via the cyanide-resistant alternative oxidase, energy is not conserved as ATP but is released as heat. A skunk cabbage can use the heat to melt snow, produce a foul stench, or attract beetles or flies. 

Complex II (succinate dehydrogenase) - Complex II is not in the path traveled by electrons from Complex I (Figure 15.3). Instead, it is a point of entry of electrons from FADH2 produced by the enzyme succinate dehydrogenase in the citric acid cycle. Both complexes I and II donate their electrons to the same acceptor, coenzyme Q. Complex II, like complex I, contains iron-sulfur proteins, which participate in electron transfer. It is also called succinate-coenzyme Q reductase because its electrons reduce coenzyme Q. 

Fig. 21.5. Components of the electron transfer chain. NADH dehydrogenase (complex 1) spans the membrane and has a proton pumping mechanism involving CoQ. The electrons go from CoQ to c5riochrome b-cl complex (complex El), and electron transfer does NOT involve complex II. Succinate dehydrogenase (complex II), glycerol 3-phosphate dehydrogenase, and ETF Q oxidoreductase (shown in blue) all transfer electrons to CoQ, but do not span the membrane and do not have a proton pumping mechanism. As CoQ accepts protons from the matrix side, it is converted to QH2. Electrons are transferred from complex III to complex IV (cytochrome c oxidase) by cytochrome c, a small cytochrome in the intermembrane space that has reversible binding sites on the b-c, complex and cytochrome c oxidase.

The respiratory chain is composed of four multiple-subunit complexes, NADH dehydrogenase (complex I), succinate dehydrogenase (complex II), cytochrome c reductase (complex III) and cytochrome c oxidase (complex IV, CcO) (7). The four complexes, located in the inner mitochondrial membrane of eukaryotes and the inner cytoplasmic membrane of prokaryotes, are electronically connected by ubiquinone and cytochrome c, which transfer electrons through complex I or complex II to complex III, and finally to complex IV, where molecular oxygen is reduced to water. Concurrently, protons are pumped across the inner mitochondrial membrane of eukaryotes or the cytoplasmic membrane of prokaryotes. The proton gradient is utilized by ATP synthase (complex V) to synthesize ATP. In many organisms, the respiratory complexes and complex V are assembled into supercomplexes which have been... 

Carboxamides are a group of fungicides that control diseases caused by Basidiomycete type fungi (42). The best known member of this group is carboxin (Figure 6). Carboxamides specifically block membrane bound succinate-ubiquinone oxldoreductase activity in the mitochondrial electron transport chain (42, ). The carboxin receptor in the succinic dehydrogenase complex (SDC) is believed to be the iron-sulfur cluster Sj complexed with small coenzyme Q binding polypeptide(s) in a phospholipid environment (45.46 >. 

Carboxamides Highly Active Against Carboxin-Resistant Succinic Dehydrogenase Complexes from Carboxin-Selected Mutants of Ustilago maydis and Aspergillus nidulans, Pestic. Biochem. Physiol, 1978, 9,165. 

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