Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.6.5.3 (complex I)
8,901 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several iron-sulfur centers in the NADH-ubiquinone segment of the respiratory chain in pigeon heart mitochondria and in submitochondrial particles were analyzed by the combined application of cryogenic EPR (between 30 and 4.2 degrees K) and potentiometric titration. Center N-1 (iron-sulfur centers associated with NADH dehydrogenase are designated with the prefix "N") resolves into two single electron titratins with EM7.2 values of minus 380 plus or minus 20 mV and minus 240 plus or minus 20 mV (Centers N-1a and N-1b, respectively). Center N-1a exhibits an EPR spectrum of nearly axial symmetry with g parellel = 2.03, g = 1.94, while that of Center N-1b shows more apparent rhombic symmetry with gz = 2.03, gy = 1.94 and gx = 1.91. Center N-2 also reveals EPR signals of axial symmetry at g parallel = 2.05 and g = 1.93 and its principal signal overlaps with those of Centers N-1a and N-1b. Center N-2 can be easily resolved from N-1a and N-1b because of its high EM7.2 value (minus 20 plus or minus 20 mV). Resolution of Centers N-3 and N-4 was achieved potentiometrically in submitochondrial particles. The component with EM7.2 = minus 240 plus or minus 20 mV is defined as Center N-3 (gz = 2.10, (gz = 2.10, (gy = 1.93?), GX = 1.87); the minus 405 plus or minus 20 mV component as Center N-4 (gz = 2.11, (gy = 1.93?), gx = 1.88). At temperatures close to 4.2 degrees K, EPR signals at g = 2.11, 2.06, 2.03, 1.93, 1.90 and 1.88 titrate with EM7.2 = minus 260 plus or minus 20 mV. The multiplicity of peaks suggests the presence of at least two different iron-sulfur centers having similar EM7.2 values (minus 260 plus or minus 20 mV); HENCE, tentatively assigned as N-5 and N-6. Consistent with the individual EM7.2 values obtained, addition of succinate results in the partial reduction of Center N-2, but does not reduce any other centers in the NADH-ubiquinone segment of the respiratory chain. Centers N-2, N-1b, N-3, N-5 and N-6 become almost completely reduced in the presence of NADH, while Centers N-1a and N-4 are only slightly reduced in pigeon heart submitochondrial particles. In pigeon heart mitochondria, the EM7.2 of Center N-4 lies much closer to that of Center N-3, so that resolution of the Center N-3 and N-4 spectra is not feasible in mitochondrial preparations. EM7.2 values and EPR lineshapes for the other iron-sulfur centers of the NADH-ubiquinone segment in the respiratory chain of intact mitochondria are similar to those obtained in submitochondrial particle preparations. Thus, it can be concluded that, in intact pigeon heart mitochondria, at least five iron-sulfur centers show EM7.2 values around minus 250 mV; Center N-2 exhibits a high EM7.2 (minus 20 plus or minus 20 mV), while Center N-1a shows a very low EM7.2 (minus 380 plus or minus 20 mV).
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PMID:Thermodynamic and EPR characterization of iron-sulfur centers in the NADH-ubiquinone segment of the mitochondrial respiratory chain in pigeon heart. 16 70

It has been reported that cells of Candida utilis, grown in continuous culture under iron-limited conditions, develop site 1 phosphorylation, without the appearance of piericidin sensitivity and without changes in the iron-sulfur centers of NADH dehydrogenase, on aeration in the presence of cycloheximide, as well as on increasing the supply of iron during growth. These findings were reinvestigated in the present study. The parameters and properties followed during these transitions were sensitivity of NADH oxidation to piericidin, presence or absence of coupling site 1, EPR signals appearing on reduction with NADH or dithionite, the specific activities of NADH oxidase, NADH-ferricyanide reductase, and NADH-5-hydroxy-1,4-naphthoquinone (juglone) reductase, and the kinetic behavior of NADH dehydrogenase in the ferricyanide assay. Monitoring the rates of oxidation of NADH in submitochondrial particles with artificial oxidants, observing the kinetics of the ferricyanide assay, and measuring the concentration of iron-sulfur centers elicited by EPR permitted ascertaining the type of NADH dehydrogenase present and its relative concentration in different experimental situations. It was found that on gradually increasing the concentration of iron during continuous culture (transition from ironlimited to iron- and substrate-limited growth), as well as on aeration of iron-limited cells, coupling site 1, piericidin sensitivity, NADH-ferricyanide activity, and iron-sulfur centers 1 and 2 increased concurrently, with concomitant decline of NADH-juglone reductase activity. Cycloheximide prevented all these changes. Iron-sulfur centers 3 plus 4 underwent relatively little increase during these transitions. It is concluded that in both of these experimental conditions a replacement of the type of NADH dehydrogenase present in exponential phase cells by that characteristic of stationary phase cells occurs and that the appearance of site 1 phosphorylation, piercidin sensitivity, and iron-sulfur centers 1 plus 2, all associated with the latter enzyme, is a consequence of this replacement. No evidence was found for the development of coupling site 1 without the appearance of piericidin sensir th
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PMID:Piericiden A sensitivity, site 1 phosphorylation, and reduced nicotinamide adenine dinucleotide dehydrogenase during iron-limited growth of Candida utilis. 16 85

Two distinct ferredosin-type iron-sulfur centers (designated as Centers S-1 and S-2) are present in the soulble succinate dehydrogenase in approximately equivalent concentrations to that of bound flavin. Both Centers S-1 and S-2 exhibit electron paramagnetic resonance absorbance in the reduced state at the same magnetic field (gz = 2.03, gy = 1.93, and gx = 1.91) with similar line shape. Center S-2 is reducible only chemically with dithionite and remains oxidized under physiological conditions. Thus, its functional role is unknown; however, thermodynamic and EPR characterization of this iron-sulfur center has revealed important molecular events related to this dehydrogenase. The midpoint potentials of Centers S-1 and S-2 determined in the soluble succinate dehydrogenase preparations are -5 +/- 15 mV and -400 +/- 15 mV, respectively, while corresponding midpoint potentials determined in particulate preparations, such as succinate-cytochrome c reductase or succinate-ubiquinone reductase, are 0 +/- 15 mV and -260 +/- 15 mV. Reconstitution of soluble succinate dehydrogenase with the cytochrome b-c1 complex is accompanied by a reversion of the Center S-I midpoint from -400 +/- 15 mV to -250 +/- 15 mV with a concomitant restoration of antimycin A-sensitive succinate-cytochrome c reductase activity. There observations indicate that, during the reconstitution process, Center S-I is restored to its original molecular environment. In the reconstitutively active succinate dehydrogenase, the relaxation time of Center S-2 is much shorter than that of S-1, thus Center S-2 spectra are well discernible only below 20 K (at 1 milliwatt of power), while the resonance absorbance of Center S-1 is detectable at higher temperatures and readily saturates below 15 K. Over a wide temperature range the power saturation of Center S-1 resonance absorbance is relieved by Center S-2 in the paramagnetic state, and the Center S-2 central resonance absorbance is broadened by Center S-1 spins, due to a spin-spin interaction between these centers. These observations indicate an adjacent location of these centers in the enzyme molecule. In reconstitutively inactive enzymes, subtle modification of the enzyme structure appears to shift the temperature dependence of Center S-2 relaxation to the higher temperature. Thus the EPR signals of Center S-2 are also detectable at higher temperature. In this system a splitting of the central peak of the Center S-2 spectrum due to spin-spin interaction was observed at extremely low temperatures, while this was not observed in reconstitutively active enzymes or in paritculate preparations. This spin-spin interaction phenomena of inactive enzymes disappeared upon chemical reactivation with concomitant appearance of the reconstitutive activity. These observations provide a close correlation between the molecular integrity of the enzyme and its physiological function.
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PMID:Thermodynamic and EPR characteristics of two ferredoxin-type iron-sulfur centers in the succinate-ubiquinone reductase segment of the respiratory chain. 17 55

(1) The EPR spectrum of Center 1 of NADH dehydrogenase in isolated Complex I or submitochondrial particles from beef heart consists of two overlapping nearly axial signals of the same intensity. They are defined as Center 1a (gll = 0.021, gl = 1.938) and Center 1b (gll = 2.021, gl = 1.928). (2) The line shape of the EPR spectrum of the Center 3+4 can be interpreted as an overlap of two rhombic signals of the same intensity. We define Center 3 by the g-values: gz=2.103, gy = 1.93-1.94, gx=1.884, and Center 4 by the values gz=2.04, gy=1.92-1.93, gx=1.863. (3) Direct quantitation of the individuals signals as well as computer stimulation suggests that the amount of the Centers 1a and 1b is only 25% of that of the other individuals centers and FMN. As EPR spectra of beef-heart submitochondrial particles at 10-20 K are nearly identical to those of Complex I, the same relative concentrations of the Fe-S centers are also present in the particles. (4) The signals either observed by us in EPR spectra of Complex I and submitochondrial particles at 4.2 K and high microwave powers can now be explained without assuming more than 5 paramagnetic centers in NADH dehydrogenase.
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PMID:EPR signals of NADH: Q oxidoreductase. Shape and intensity. 18 11

1. From the 57Fe hyperfine interaction in EPR spectra of reduced submitochondrial particles from the yeast Candida utilis, grown with 57Fe, it is concluded that all Fe-S centers in these particles detectable in spectra at 35-80 K are [2Fe-2S]2-(2-; 3-) centers. These are the centers 1 of NADH and succinate dehydrogenase, the Rieske Fe-S center and possibly center 2 of succinate dehydrogenase. 2. The signals of the reduced particles detectable only at temperatures below 20 K are [4Fe-4S]2-(2-; 3-) clusters. These are the centers 2,3 and 4 of NADH dehydrogenase. 3. EPR spectra of the [2Fe-2S]3- centers of Complex I and II, but not that of Complex III, display a great inequality of the Fe nuclei in the effective hyperfine interaction in the x-y direction.
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PMID:The number of Fe atoms in the iron-sulphur centers of the respiratory chain. 19 54

Oxidation factor, a protein required for electron transfer from succinate to cytochrome c in the mitochondrial respiratory chain, has been purified from isolated succinate . cytochrome c reductase complex. Purification of the protein has been followed by a reconstitution assay in which restoration of ubiquinol . cytochrome c reductase activity is proportional to the amount of oxidation factor added back to depleted reductase complex. The purified protein is a homogeneous polypeptide on acrylamide gel electrophoresis in sodium dodecyl sulfate and migrates with an apparent Mr = 24,500. Purified oxidation factor restores succinate . cytochrome c reductase and ubiquinol . cytochrome c reductase activities to depleted reductase complex. It is not required for succinate dehydrogenase nor for succinate . ubiquinone reductase activities of the reconstituted reductase complex. Oxidation factor co-electrophoreses with the iron-sulfur protein polypeptide of ubiquinol . cytochrome c reductase complex. The purified protein contains 56 nmol of nonheme iron and 36 nmol of acid-labile sulfide/mg of protein and possesses an EPR spectrum with the characteristic "g = 1.90" signal identical to that of the iron-sulfur protein of the cytochrome b . c1 complex. In addition, the optimal conditions for extraction of oxidation factor, including reduction with hydrosulfite and treatment of the b . c1 complex with antimycin, are identical to those which facilitate extraction of the iron-sulfur protein from the b . c1 complex. These results indicate that oxidation factor is a reconstitutively active form of the iron-sulfur protein of the cytochrome b . c1 complex first discovered by Rieske and co-workers (Rieske, J.S., Maclennan, D.H., and Coleman, R. (1964) Biochem. Biophys. Res. Commun. 15, 338-344) and thus demonstrate that this iron-sulfur protein is required for electron transfer from ubiquinol to cytochrome c in the mitochondrial respiratory chain.
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PMID:Purification of a reconstitutively active iron-sulfur protein (oxidation factor) from succinate . cytochrome c reductase complex of bovine heart mitochondria. 22 62

The temperature dependence of EPR spectra of oxidized [4Fe-4S](-1,-2) ferredoxins (previously designated HiPIP) and a reduced [4Fe-4S](-2,-3) ferredoxin have been analyzed so as to determine the energy of a low-lying excited electronic state. The values obtained were: Center S-3 from beef heart, 44 cm-1; Center S-3 from mung bean, 53 cm-1; the [4Fe-4S](-1,-2) ferredoxin from Thermus thermophilus, 78 cm-1; Center N-2 of NADH ubiquinone reductase, 83 cm-1. Increasing axial distortion in the EPR spectra of the [4Fe-4S](-1,-2), ferrodoxins was associated with higher energy differences. Center N-2, a [Fe-4S](-2,-3) iron-sulfur cluster does not fit this relationship.
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PMID:Exchange integral for a variety of tetranuclear ferredoxins. 22 31

The electron spin relaxation of iron-sulphur centres and ubisemiquinones of plant mitochondria was studied by microwave power saturation of the respective EPR signals. In the microwave power saturation technique, the experimental saturation data were fitted by a least-squares procedure to a saturation function which is characterized by the power for half-saturation (P1/2) and the inhomogeneity parameter (b). Since the theoretical saturation curves were based on a one-electron spin system, it became possible to differentiate between EPR signals of iron-sulphur centres which have similar g values but different P1/2 values. If the difference in the P1/2 values of the overlapped components was small, no significant deviation from these theoretical saturation curves was observed, as shown for the overlapped signals of centre S-3 and the Ruzicka centre of mung bean mitochondria. By contrast, the microwave power saturation data for the g = 1.93 signal (17--26 K) of Arum maculatum submitochondrial particles reduced by succinate could not be fitted using one-electron saturation curves. Reduction by NADH resulted in a stronger deviation. Since the iron-sulphur centres of Complex I were present only in an unusually low concentration in A. maculatum mitochondria, it was proposed that an iron-sulphur centre of the external NADH dehydrogenase contributes to the spectrum of centre S-1. For mung bean mitochondria, the g = 1.93 signal below 20 K could be attributed mainly to centre N-2. The microwave power saturation technique was also suitable for detecting magnetic interactions between paramagnetic centres. From the saturation data of the complex spectrum attributable to centre S-3 and an interacting ubisemiquinone pair in mung bean mitochondria (oxidized state) followed that centre S-3 has a faster electron spin relaxation than the ubisemiquinone molecules. It is noteworthy that the differences in the relaxation rates were maintained despite the interaction between centre S-3 and the ubisemiquinones. Furthermore, a relaxation enhancement was observed for centre S-1 of A. maculatum submitochondrial particles upon reduction of centre S-2 by dithionite. This indicated a magnetic interaction between centres S-1 and S-2.
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PMID:Characterization of iron-sulphur centres of plant mitochondria by microwave power saturation. 22 32

The concentration of the iron-sulphur (Fe-S) cluster 1b, present in complex I or soluble high-molecular-mass NADH dehydrogenase, was determined using different methods. It was found that direct double integration of the EPR signal at temperatures higher than 40 K, as is commonly used in this field of research, results in a considerable overestimation of the concentration of cluster 1b. It is demonstrated that this is caused by contributions from the relaxation-broadened signals of the Fe-S clusters 2-4 in the enzyme. The correct way for determining the intensity of the EPR signal of cluster 1b is by comparison with a simulated line shape. It is concluded that the concentration of cluster 1b is half that of cluster 2. This corroborates our proposal based on presteady-state kinetic and inhibitor-titration studies [Van Belzen, R., Van Gaalen, M. C. M., Cuypers, P. A. & Albracht S. P. J. (1990) Biochim. Biophys Acta 1017, 152-159] that the minimal functional unit of mitochondrial NADH:ubiquinone oxidoreductase must be a heterodimer.
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PMID:On the stoichiometry of the iron-sulphur clusters in mitochondrial NADH: ubiquinone oxidoreductase. 133 May 59

NADH:ubiquinone oxidoreductase (complex I) was purified from bovine heart mitochondria by solubilization with n-dodecyl beta-D-maltoside (lauryl maltoside), ammonium sulfate fractionation, and chromatography on Mono Q in the presence of the detergent. Its subunit composition was very similar to complex I purified by conventional means. Complex I was dissociated in the presence of N,N-dimethyldodecylamine N-oxide and beta-mercaptoethanol, and two subcomplexes, I alpha and I beta, were isolated by chromatography. Subcomplex I alpha catalyzes electron transfer from NADH to ubiquinone-1. It is composed of about 22 different and mostly hydrophilic subunits and contains 2.0 nmol of FMN/mg of protein. Among its subunits is the 51-kDa subunit, which binds FMN and NADH and probably contains a [4Fe-4S] cluster also. Three other potential Fe-S proteins, the 75- and 24-kDa subunits and a 23-kDa subunit (N-terminal sequence TYKY), are also present. All of the Fe-S clusters detectable by EPR in complex I, including cluster 2, are found in subcomplex I alpha. The line shapes of the EPR spectra of the Fe-S clusters are slightly broadened relative to spectra measured on complex I purified by conventional means, and the quinone reductase activity is insensitive to rotenone. Similar changes were found in samples of the intact chromatographically purified complex I, or in complex I prepared by the conventional method and then subjected to chromatography in the presence of lauryl maltoside. Subcomplex I beta contains about 15 different subunits. The sequences of many of them contain hydrophobic segments that could be membrane spanning, including at least two mitochondrial gene products, ND4 and ND5. The role of subcomplex I beta in the intact complex remains to be elucidated.
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PMID:Resolution of NADH:ubiquinone oxidoreductase from bovine heart mitochondria into two subcomplexes, one of which contains the redox centers of the enzyme. 133 58


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