Complexes electron transport

Complex I catalyzes an NADH-CoQ reductase activity, and it contains the NADH dehydrogenase flavoprotein. It has two types of electron-carrying structures FMN and several iron-sulfur centers. FMN is a tightly bound prosthetic group of the dehydrogenase enzyme, and it is reduced to FMNH2 by the two reducing equivalents derived from NADH  

The electrons from FMNH2 are transferred to the next electron carrier, coenzyme Q, via the iron-sulfur centers of the NADH-CoQ reductase. The iron-sulfur centers consist of iron atoms paired with an equal number of acid-labile sulfur atoms. The respiratory chain iron-sulfur clusters are of the Fe2S2 or Fe4S4 type. The iron atom, present as nonheme iron, undergoes oxidation-reduction cycles (Fe + Fe + -t- e ). In the Fe4S4 complexes, the centers 

Transport of reducing equivalents from NADH to FMN and structure of the iron-sulfur protein complex that mediates electron transport from FMNH2 to CoQ. Both FMN and the iron-sulfur centers are components of NADH-CoQ 

Inhibitors of NADH-CoQ reductase rotenone (a toxic plant product), piericidin A (an antibiotic), and amytal (a barbiturate). 

Inhibitors of complex II. (a) Oxaloacetate, (b) malonate, (c) thenoyltrifluoroacetone, and (d) carboxin. 

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Complexes III and IV have Fe-porphyrin prosthetic groups (hemes), complex IV also contains copper atoms which are involved in electron transport. Complexes I, III, and IV use the energy of electron transport to pump protons out of the matrix so as to maintain a pH gradient and an electrical potential difference across the inner membrane required for ATP synthesis (see below and Appendix 3). It is important to remember that all dehydrogenations of metabolic substrates remove two protons as well as two electrons and that a corresponding number of protons are consumed in the final reduction of dioxygen (Figures 5, 6). 

Function and Assembly of Electron-Transport Complexes in Desulfovibrio vulgaris Hildenborough... 

A Transport inhibitors bind to one of the electron transport complexes and block the transfer of electrons to oxygen, thus interfering with the ability to create a proton gradient (Table 7-2). 

Conrad, H. E., K. Lieb, and I. C. Gunsalus, Mixed function oxidation. III. An electron transport complex in camphor ketolactonization , J. Biol. Chem., 240,4029-4037 (1965). 

The mechanism of oxidation of NADH in the electron transport chain appears to occur by transfer of a hydrogen atom together with two electrons (a hydride ion H ). Oxidation of FADH2 to FAD might occur by transfer of two hydrogen atoms or by transfer of H + H+. However, it is useful to talk about all of these compounds as electron carriers with the understanding that movement of one or both of the electrons may be accompanied by transfer of H+. The electron transport complex is pictured in a very simplified form in Fig. 10-5. 

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. 

What are the structures of the individual electron transport complexes What are the subunit compositions What cofactors are present How are electrons transferred How are protons pumped We will consider these questions for each of complexes I-IV, as found in both prokaryotes and eukaryotes.88d e... 

What chemical properties are especially important for the following compounds in the electron transport complexes of mitochondria ... 

According to the chemiosmotic theory, flow of electrons through the electron-transport complexes pumps protons across the inner membrane from the matrix to the intermembrane space. This raises the pH in the matrix and leaves the matrix negatively charged with respect to the intermembrane space and the cytosol. Protons flow passively back into the matrix through a channel in the ATP-synthase, and this flow drives the formation of ATP. 

Finally, the importance of molecular and supramolecular organization of the photosynthetic membranes (namely, the distribution of the Chl-protein and electron transport complexes in the different regions of the membranes when they are appressed to form grana) will be discussed in relation to its influence on light energy distribution between the two photosystems and on electron transport. 

Most of the thylakoid proteins are organized into four intrinsic protein complexes PS II complex, Cyt b/f complex, PS I complex and ATP synthetase (Fig. 1). The electron transport complexes are linked by mobile electron transport carriers, plastoquinone, plastocyanin and ferredoxin (see Chapter 10). Furthermore, chloroplasts that possess Chi b have the major light-harvesting Chi a/h-proteins of PS II (LHC II) that may represent over 50% of the thylakoid protein [13], as well... 

The Cyt bIf complex is the only electron transport complex for which the transmembrane organization of all its subunits is established. This membrane-spanning complex that functions as an intermediate electron transport complex between PS II and PS I, and translocates protons across the membrane from the stroma to the lumen, contains 4 proteins Cyt / (33 kDa), Cyt 6-563 (23 kDa), the Rieske Fe-S protein (20 kDa) and the unnamed 17 kDa protein. 

The matrix is viscous and contains all TCA cycle enzymes except succinate dehydrogenase, which is a component of electron transport complex II and is located within... 

Orientation of the components of the electron transport complexes within the inner mitochondrial membrane. Fe-S = Iron-sulfur center b, c, c, a, and 03 = cytochromes Cu = copper ion. 

Of the herbicides discussed, paraquat and DCMU are most hazardous to humans. Paraquat generates free radicals that can attack cell components. DCMU poisons the electron transport complex. 

Pyruvate is converted to acetyl CoA with the formation of NADH, and fatty acids (attached to CoA) are also converted to acetyl CoA with formation of NADH and FADH. Oxidation of acetyl CoA in the citric acid cycle generates NADH and FADH2. Stage 2 Electrons from these reduced coenzymes are transferred via electron-transport complexes (blue boxes) to O2 concomitant with transport of H ions from the matrix to the intermembrane space, generating the proton-motive force. Electrons from NADH flow directly from complex I to complex III, bypassing complex II. 

CoQ and Three Electron-Transport Complexes Pump Protons Out of the Mitochondrial Matrix... 

A EXPERIMENTAL FIGURE 8-25 Mitochondrial particles are required for ATP synthesis, but not for electron transport. "Inside-out" membrane vesicles that lack Fi and retain the electron transport complexes are prepared as indicated. Although these can transfer electrons from NADFI to O2, they cannot synthesize ATR The subsequent addition of F-, particles reconstitutes the native membrane structure, restoring the capacity for ATP synthesis. When detached from the membrane, F-, particles exhibit ATPase activity. 

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