Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phospholipid requirement of membrane-bound enzymes may depend on several reasons. In our laboratory we have investigated lipids (1) as a bidimensional medium required for the movement of Coenzyme Q, a lipid-soluble cofactor of the mitochondrial respiratory chain, and (2) as a hydrophobic environment necessary to impose the proper conformation to membrane-bound enzymic proteins. We have found that Coenzyme Q, once reduced by NADH dehydrogenase, must cross the inner mitochondrial membrane; only quinones having long isoprenoid side chains can easily cross phospholipid bilayers, and this is the reason why a short chain quinone such as CoQ-3 inhibits NADH oxidation. The incapability of short quinones to cross lipid bilayers is due to their disposition in the lipid bilayer, stacked within the phospholipids. The conformational role of lipids has been investigated indirectly observing the kinetics of membrane-bound enzymes, e.g. the mitochondrial ATPase, and directly by circular dichroism. Lipid removal or lipid perturbation with organic solvents induce a decrease of alpha-helical content in mitochondrial proteins, and give rise to a series of kinetic changes in ATPase, including uncompetitive inhibition, increased activation energy, and loss of cooperativity in oligomycin inhibition. The recognition of a conformational role of lipids has allowed us to postulate a working hypothesis for the mechanism of action of general anesthetics. Such drugs have been found by us, by means of spin labels and fluorescent probes, to disrupt lipid protein interactions in several membranes, including synaptic membranes. The loosening of such interactions is believed to induce conformational changes, which will alter ion transport systems necessary to the propagation of neural impulses. Conformational changes induced by anesthetics have been found by us both directly by circular dichroism and indirectly by enzyme kinetics. The conformational effect of anesthetics is not directly exerted on the proteins but is mediated through the lipids. In agreement with this hypothesis we have found that membrane-bound acetylcholinesterase is inhibited by anesthetics, whereas the solubilized enzyme is not inhibited. However, binding of the solubilized enzyme to phospholipids restores anesthetic inhibition.
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PMID:Biophysical studies on agents affecting the state of membrane lipids: biochemical and pharmacological implications. 15 58

Ubiquinone cytochrome c reductase (complex III) in detergent dispersion has been cross-linked with two reversible cross-linking agents dithiobissuccinimidylpropionate and dimethyl-3.3'-dithiobispropionimidate and the cross-linked products formed have been analyzed by two-dimensional gel electrophoresis. Under mild reaction conditions, polypeptides I and II, II and VI, I and V, and VI and VII were the most prominent subunit pairs seen. With higher levels of reagent, larger aggregates were produced until an aggregate of apparent molecular weight 310 000 was the dominant band on gels. This is the complex III monomer.
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PMID:Nearest neighbor relationships of the polypeptides in ubiquinone cytochrome c reductase (complex III). 19 17

1. Whole cells of Methylomonas Pl1 contained ubiquinone, identified as ubiquinone-8. No naphthaquinone was detected. Ubiquinone was located predominantly in the particulate fraction, which also contained most of the NADH oxidase activity. 2. Aerobic incubation of cells with formaldehyde or methanol resulted in about 20% reduction of ubiquinone, irrespective of the presence or absence of dinitrophenol. On inhibition of the respiration by cyanide, ubiquinone became partly reduced by endogenous substrates (15--25%), and a further reduction occurred only in the presence of formaldehyde (up to 60%). When endogenous substrates were completely exhausted, then 44 and 23% of ubiquinone was reduced by formaldehyde or methanol respectively. 3. The difference spectra at room and liquid-N2 temperatures revealed the presence of cytochrome b and two cytochromes c (c-552.5 and c-549) all tightly bound to the membrane. Cytochrome c-552.5 was also found in the soluble fraction. 4. Redox changes of cytochromes b and c, with methanol or formaldehyde as substrates, respond to the aerobic and anaerobic states of the cell and to KCN inhibition in a manner characteristic of the electron carriers of the respiratory chain. 5. The merging point for electron transport from NADH dehydrogenase and formaldehyde dehydrogenase is suggested to be at the level of ubiquinone.
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PMID:The respiratory chain of a newly isolated Methylomonas Pl1. 41 43

A thirty-two year old female had chronic progressive external ophthalmoplegia (CPEO), exertional fatigue, dysarthria, dysphagia, and bilateral hearing impairment. Histochemical stains, obtained from the right vastus lateralis, showed ragged-red fibers and wide-spread abnormalities in the number, size, and the structure of mitochondria under electronomicroscopic examination. A biochemical analysis showed a low activity of NADH-cytochrome C reductase, NADH dehydrogenase and a normal activity of succinate cytochrome C reductase and cytochrome C oxidase. This data suggests a specific defect in the NADH dehydrogenase of complex I (NADH CoQ reductase). We believe that this is the first biochemically defined mitochondrial myopathy reported in Taiwan and provides additional evidence for the existence of biochemical heterogeneity in mitochondrial disorders of CPEO.
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PMID:Chronic progressive external ophthalmoplegia with NADH-CoQ reductase deficiency: report of a case. 132 93

We have investigated the role of the Coenzyme Q pool in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. Antimycin A and myxothiazol inhibit glycerol-3-phosphate cytochrome c oxidoreductase in a sigmoidal fashion, indicating that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III. The inhibition of ubiquinol cytochrome c reductase is linear at low concentrations of both inhibitors, indicating that sigmoidicity of antimycin A and myxothiazol inhibition is not a direct property of antimycin A and myxothiazol binding. Glycerol-3-phosphate cytochrome c oxidoreductase is strongly stimulated by added CoQ3, indicating that endogenous CoQ is not saturating. Application of the pool equation for nonsaturating ubiquinone allows calculation of the Km for endogenous CoQ of glycerol-3-phosphate dehydrogenase of 3.14 mM. The results of this investigations reveal that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III in brown adipose tissue mitochondria; moreover, its concentration is far below saturation for maximal electron transfer activity in comparison with other branches of the respiratory chain connected with the CoQ pool. HPLC analysis revealed a lower amount of CoQ in brown adipose mitochondria (0.752 nmol/mg protein) in comparison with mitochondria from other tissues and the presence of both CoQ9 and CoQ10.
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PMID:Coenzyme Q-pool function in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. 132 18

The saturation kinetics of NADH and succinate oxidation for Coenzyme Q (CoQ) has been re-investigated in pentane-extracted lyophilized beef heart mitochondria reconstituted with exogenous CoQ10. The apparent 'Km' for CoQ10 was one order of magnitude lower in succinate cytochrome c reductase than in NADH cytochrome c reductase. The Km value in NADH oxidation approaches the natural CoQ content of beef heart mitochondria, whereas that in succinate oxidation is close to the content of respiratory chain enzymes.
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PMID:Saturation kinetics of coenzyme Q in NADH and succinate oxidation in beef heart mitochondria. 132 77

Coenzyme Q is required in the electron transport system of rat hepatocyte and human erythrocyte plasma membranes. Extraction of coenzyme Q from the membrane decreases NADH dehydrogenase and NADH:oxygen oxidoreductase activity. Addition of coenzyme Q to the extracted membrane restores the activity. Partial restoration of activity is also found with alpha-tocopherylquinone, but not with vitamin K1. Analogs of coenzyme Q inhibit NADH dehydrogenase and oxidase activity and the inhibition is reversed by added coenzyme Q. Ferricyanide reduction by transmembrane electron transport from HeLa cells is inhibited by coenzyme Q analogs and restored with added coenzyme Q10. Reduction of external ferricyanide and diferric transferrin by HeLa cells is accompanied by proton release from the cells. Inhibition of the reduction by coenzyme Q analogs also inhibits the proton release, and coenzyme Q10 restores the proton release activity. Trans-plasma membrane electron transport stimulates growth of serum-deficient cells, and added coenzyme Q10 increases growth of HeLa (human adenocarcinoma) and BALB/3T3 (mouse fibroblast) cells. The evidence is consistent with a function for coenzyme Q in a trans-plasma membrane electron transport system which influences cell growth.
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PMID:Requirement for coenzyme Q in plasma membrane electron transport. 145 89

Purified ubiquinol-cytochrome c reductase of beef heart mitochondria is very stable in aqueous solution; it suffers little damage upon illumination with visible light under aerobic or anaerobic conditions. However, it is rapidly inactivated when the photosensitizer hematoporphyrin is present during illumination. The hematoporphyrin-promoted photoactivation is dependent on sensitizer dose, illumination time, and oxygen. Singlet oxygen is shown to be the destructive agent in this system. The photoinactivation of ubiquinol-cytochrome c reductase is prevented by excess exogenous ubiquinone, regardless of its redox state. This protective effect is not due to protein-ubiquinone interactions but to the singlet oxygen scavenger property of ubiquinone. Ubiquinone also protects against hematoporphyrin-promoted photoinactivation of succinate-ubiquinone reductase and cytochrome c oxidase. The photoinactivation site in ubiquinol-cytochrome c reductase is the iron-sulfur cluster of Rieske's protein. Two histidine residues, presumably serving as two ligands for the iron-sulfur cluster of Rieske's protein, are destroyed. No polypeptide bond cleavage is detected. Photoinactivation has little effect on the spectral properties of cytochromes b and c1 but alters their reduction rates substantially. this photoinactivation also causes the formation of proton-leaking channels in the complex. When the photoinactivated reductase is co-inlaid with intact ubiquinol-cytochrome c reductase or cytochrome c oxidase in a phospholipid vesicle, no proton ejection can be detected during the oxidation of their corresponding substrates.
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PMID:Hematoporphyrin-promoted photoinactivation of mitochondrial ubiquinol-cytochrome c reductase: selective destruction of the histidine ligands of the iron-sulfur cluster and protective effect of ubiquinone. 184 89

This study examines the possible role of Coenzyme Q (CoQ, ubiquinone) in the control of mitochondrial electron transfer. The CoQ concentration in mitochondria from different tissues was investigated by HPLC. By analyzing the rates of electron transfer as a function of total CoQ concentration, it was calculated that, at physiological CoQ concentration NADH cytochrome c reductase activity is not saturated. Values for theoretical Vmax could not be reached experimentally for NADH oxidation, because of the limited miscibility of CoQ10 with the phospholipids. On the other hand, it was found that CoQ3 could stimulate alpha-glycerophosphate cytochrome c reductase over three-fold. Electron transfer being a diffusion-coupled process, we have investigated the possibility of its being subjected to diffusion control. A reconstruction study of Complex I and Complex III in liposomes showed that NADH cytochrome c reductase was not affected by changing the average distance between complexes by varying the protein: lipid ratios. The results of a broad investigation on ubiquinol cytochrome c reductase in bovine heart submitochondrial particles indicated that the enzymic rate is not diffusion-controlled by ubiquinol, whereas the interaction of cytochrome c with the enzyme is clearly diffusion-limited.
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PMID:Studies on the role of ubiquinone in the control of the mitochondrial respiratory chain. 235 8

Ragged-red fibers (RRFs) are mainly seen in mitochondrial myopathy and related to biochemical defects in electron transfer chain on some occasions. Recently, some papers reported the occurrence of RRFs in the biopsied muscle of myotonic dystrophy (MyD). To examine whether the mitochondrial function is disturbed in MyD, we have studied the biopsied muscles of 12 cases with MyD (10 males and 2 females averaging 38 years of age) morphologically and mainly biochemically. RRFs, ranging from 2--20% of the muscle fibers, were identified in 5 out of 12 cases. On electron microscopy, these fibers had aggregated abnormally enlarged mitochondria with dene bodies, concentrically whirled membranous cristae and paracrystalline inclusions. Clinically, 4 of 5 cases with RRFs had mild to moderate and only 2 of 7 without RRFs had ophthalmoplegia. Bicycle ergometer exercise test showed abnormal increase of lactate/pyruvate ratio in three cases with RRFs. Histochemically, cytochrome c oxidase (CCO) activity was absent selectively in all of the RRFs. Immunohistochemical staining showed the presence of CCO protein by using monoclonal antibody which was specific to CCO subunit IV. Biochemical study with crude muscle extract of 11 cases of MyD showed decreases in NADH dehydrogenase, NADH CoQ reductase, succinate CoQ reductase (SCR), CCO, carnitine actyl transferase activities in most of cases regardless RRFs. To avoid the influence possibly derived from the various stages of muscle degeneration in the biopsied specimens, we calculated the ratio of the enzyme activities compared with succinate dehydrogenase which was located in the electron transfer chain and did not show any statistical difference regardless of RRFs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[A study of mitochondrial electron transfer chain in myotonic dystrophy]. 259 36


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