Succinate dehydrogenase location

The space inside the inner mitochondrial membrane is called the matrix, and it contains most of the enzymes of the TCA cycle and fatty acid oxidation. (An important exception, succinate dehydrogenase of the TCA cycle, is located in the inner membrane itself.) In addition, mitochondria contain circular DNA molecules, along with ribosomes and the enzymes required to synthesize proteins coded within the mitochondrial genome. Although some of the mitochondrial proteins are made this way, most are encoded by nuclear DNA and synthesized by cytosolic ribosomes. 

FADH is produced by succinate dehydrogenase in the citric acid cycle and by the a-glycerol phosphate shuttle. Both enzymes are located in the inner membrane and can reoxidize FADHj directly by transferring electrons into the ETC. Once FADH2 has been oxidized, the FAD can be made available once again for use by the enzyme. 

Acetyl-CoA is oxidized to C02 by the Krebs cycle, also called the tricarboxylic acid cycle or citric acid cycle. The origin of the acetyl-CoA may be pyruvate, fatty acids, amino acids, or the ketone bodies. The Krebs cycle may be considered the terminal oxidative pathway for all foodstuffs. It operates in the mitochondria, its enzymes being located in their matrices. Succinate dehydrogenase is located on the inner mitochondrial membrane and is part of the oxidative phosphorylation enzyme system as well (Chapter 17). The chemical reactions involved are summarized in Figure 18.7. The overall reaction from pyruvate can be represented by Equation (18.5) ... 

Membranes of extremely halophilic bacteria oxidize NADH in the presence of a variety of redox dyes, including menadione [103] and DCIP [100]. The enzyme, which is located on the inner aspect of the cytoplasmic membrane [104], has been used as a marker of vesicle orientation [20]. However, a second marker should be used in conjunction with menadione reductase as there are indications that the location of the dehydrogenase may be randomized during membrane preparation [105]. A similar situation occurs with respect to the ATPase activities in Micrococcus lysodeikticus [106] and E. coli [75,107] as well as the NADH and succinate dehydrogenases from E. co/f [75,108]. The orientation of the NADH dehydrogenase in the case of H. saccharovorum does not correspond... 

The succinate dehydrogenase of S. acidocaldarius (DSM 639) is located in the cytoplasmic and membrane fractions when cells are disrupted either by sonication or decompressive disruption. About 10-30% of the activity is associated with the membrane fraction [30]. The purified membrane-bound succinate dehydrogenase activity (M, 141 000) consists of four subunits (Mr 66000, 31 000, 28 000, and 12,800). The enzyme contains a covalently-bound flavin as well as iron and acid-labile sulfide but no cytochrome [111]. The dehydrogenase reduces the following acceptors (listed in order of decreasing... 

B. In the conversion of isocitrate (Compound A) to fumarate (Compound B), 2 C02, NADH (which contains niacin), 1 GTP, and 1 FADH2 are produced. A total of approximately 9 ATP are generated. The enzymes for these reactions are all located in the mitochondrial matrix except succinate dehydrogenase, which is in the inner mitochondrial membrane. GTP does not drive any of the reactions. 

The TCA cycle is the major final common pathway of oxidation of carbohydrates, lipids, and proteins, since their oxidation yields acetyl-CoA. Acetyl-CoA also serves as precursor in the synthesis of fatty acids, cholesterol, and ketone bodies. All enzymes of the cycle are located in the mitochondrial matrix except for succinate dehydrogenase, which is embedded in the inner mitochondrial membrane. Thus, the reducing equivalents generated in the cycle have easy access to the electron transport chain. TCA cycle enzymes, with the exception of a-ketoglutarate dehydrogenase complex and succinate dehydrogenase, are also present outside the mitochondria. The overall TCA cycle is shown in Figure 13-12. 

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... 

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... 

The lipid-soluble ubiquinone (Q) is present in both bacterial and mitochondrial membranes in relatively large amounts compared to other electron carriers (Table 18-2). It seems to be located at a point of convergence of the NADH, succinate, glycerol phosphate, and choline branches of the electron transport chain. Ubiquinone plays a role somewhat like that of NADH, which carries electrons between dehydrogenases in the cytoplasm and from soluble dehydrogenases in the aqueous mitochondrial matrix to flavoproteins embedded in the membrane. Ubiquinone transfers electrons plus protons between proteins within the... 

The glycerol-3-P is then reoxidized to dihydroxyacetone-P by Flavoprotein dehydrogenase. This enzyme is situated on the inner mitochondrial membranes outer surface. It uses FAD to oxidize the glycerol-3-P to dihydroxyacetone-P, passing the electrons to CoQ (note the similarity to succinate DH, except for the location on the outer instead of the inner surface of the membrane). The organism can thus get 1.5 ATP equivalents for this NADH. 

MPP+ is a potent inhibitor of oxidation of the NAD+-linked substrates pyruvate/malate and glu-tamate/malate in isolated rat liver and brain mitochondria, while leaving the oxidation of succinate unaffected (Nicklas et al., 1985). The locus of inhibition of the mitochondrial respiration is assumed to be between the highest potential Fe-S cluster in NADH dehydrogenase and the coenzyme Q located probably at the rotenone-binding site (Ramsay et al., 1991). As a consequence of inhibition of respiration, cellular energy supplies in the form of ATP would rapidly be consumed, followed by depolarization of membranes, probable Ca influx and overstimulation of Ca +-dependent lysosomal enzymes. 

Rotenone is used experimentally as an inhibitor of mitochondrial respiration. It has little effect on the mitochondrial oxidation of succinate, but it powerfully inhibits all oxidations which operate via NADH dehydrogenase. The site of inhiUtion by rotenone has been located on the oxygen side of the nonheme iron of NADH dehydrogenase (see Respiratory chain). Piericidin and amytal appear to act at or very close to the same site. [W. W. Wainio The Mammalum Mitochondrial Respiratory Chain (Academic Press, 1970) T.P. Singer M. Gutman Adv. Enzmol. 34 (1971) 79-153 J.B.Harbome, T.J.Mabry H.Mabry eds. TTie Flavonoids (Chapman Hall, 1975)] rRNA ribosomal RNA (see Ribosomes). 

The main purpose of the glyoxylate cycle (Figure 12.7) which is located in glyoxysomes of plants is the synthesis of succinate from which carbohydrate may be produced. The reaction sequence utilizes organelle-specific isoenzymes of three enzymes of the tricarboxylate cycle citrate synthase, aconitate hydratase and malate dehydrogenase. These enzymes together with two enzymes... 

Mitochondria and unicellular organisms. Bacteria have no mitochondria. Being of mitochondrial size, the bacterium has to function as its own mitochondrion its plasma membrane, although it lacks aristae, has to attempt to carry out as many as it can of the complex activities of eukaryotic mitochondria. Hence many of the typical enzymes of eukaryotic mitochondria are located in the bacterial plasma membrane (De Ley and Docky, i960 Mitchell and Moyle, 1956a). In particular, the enzymes of the tricarboxylic acid cycle are found there. More than 90% of the cell s succinic, malic, lactic, and formic dehydrogenases, as well as the cytochrome oxidase, are present in the plasma membrane of typical bacteria, e.g. Staphylococcus aureus and Micrococcus lysodeikticus (Mitchell, 1961,1963). 

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