Dehydrogenase and oxidase complexe

The multisubunit complexes of the respiratory chain. Complexes I (NADH dehydrogenase) and II (succinate dehydrogenase) transfer electrons from NADH and succinate to UQ. Complex III (the cytochrome bc complex) transfers electrons from UQH2 to cytochrome c, and complex IV (cytochrome oxidase), from cytochrome c to 02. The arrows represent paths of electron flow. NADH and succinate provide electrons from the matrix side of the inner membrane, and 02 removes electrons on this side. Cytochrome c is reduced and oxidized on the opposite side of the membrane, in the lumen of a crista or in the intermembrane space. 

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).

FIGURE 1. Respiratory chain the enzymes of the mitochondrial iimer membrane involved in oxidative phosphorylation. From complex I to V, they are NADH-dehydrogenase, succinate dehydrogenase, cytochrome bc complex, and cytochrome c oxidase. Protons are translocated across the membrane while electrons are transferred to Oj through the chain. The proton gradient is used by ATP synthase (complex V) to make ATP. (Reprinted with permission from Saraste, 1999, American Association for the Advancement of Science.)... 

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. 

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...

In a fifth method (International Reagents Corp., Kokusai-Kobe, Japan), its first reagent contains the detergent cal-ixarene that converts LDL to a soluble complex. Cholesterol esters of HDL-C and VLDL-C are preferentially hydrolyzed by a cholesterol esterase (chromobacterium), cholesterol oxidase, and hydrazine, which divert the accessible cholesterol to cholestenone hydrazone. A second reagent with deoxycholate brealcs up the LDL-calixarene complex, allowing LDL-C to react with the esterase, a dehydrogenase, and P-NAD to yield cholestenone and fi-NADH, the latter measured by a spectrophotometer. 

Several important mammalian enzymes, such as sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase, require molybdenum as a cofactor. This organic component is a molybdopterin complex.Sulfite oxidase is probably the most important enzyme in relation to human health. This enzyme catalyzes the last step in the degradation of sulfur amino acids, oxidizing sulfite to sulfate and transferring electrons to cytochrome c. Xanthine dehydrogenase and aldehyde oxidase hydroxylate a number of heterocyclic substances, such as purines, pteridines, and others. ... 

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