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)

(1) The steady-state kinetics of the NADH dehydrogenase activity of Type-II (low molecular weight) NADH dehydrogenase with the acceptors ferricyanide, cytochrome c and 2,6-dichloroindophenol are consistent with the simultaneous operation of an ordered and a ping-pong mechanism. Thus, depending on the acceptor concentration, the reduced enzyme is preferentially oxidized before or after NAD+ disociates from it. (2) The acceptors are able to oxidize the reduced enzyme and its NAD+ complex equally well. In contrast to the kinetics of the Type-I (high molecular weight) enzyme, double substrate inhibition is not found, implying that the site of oxidation of the reduced enzyme by acceptors and the NADH-binding site are remote. (3) With the indophenol, in the concentration range measured, the ordered mechanism is mainly operative. At infinite NADH and acceptor concentrations the rate constant of the reduction of enzyme by bound NADH is measured. (4) With ferricyanide and cytochrome c, in the concentration range measured, erroneous conclusions may be drawn from extrapolations owing to the fact that extrapolated lines in double-reciprocal plots of turnover number against acceptor concentration, at different NADH concentrations, intersect in the third quadrant. A method is described that allows the extrapolation of these data to zero acceptor concentrations. (5) The relation between activity and NADH concentration is sigmoidal (h = 2.0) with ferricyanide or cytochrome c as acceptor, but hyperbolic with 2,6-dichloroindophenol. The latter is also an inhibitor, competitive with respect to NADH. It is concluded that this two-electron acceptor, like ubiquinone, acts as an allosteric effector. (6) Type II is isolated from Type I without gross changes in tertiary structure, as judged by the unaltered rate constants of dissociation of NADH (k-1) and NAD+ (k4) and association of NADH (k1). (7) Type II differs from Type I in two respects, (a) The accessibility of the acceptors is greater by at least two orders of magnitude (k3). (b) The redox potential of the prosthetic group FMN is 120 mV less, as judged by a drop in the value of k2 by four orders of magnitude. It is suggested that one or more of the iron-sulphur proteins present in Type-I but lacking in Type-II dehydrogenase functions as an effector, regulating the redox potential of the FMN.
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PMID:Steady-state kinetics of low molecular weight (type-II) NADH dehydrogenase. 18 Oct 90

1. The electron paramagnetic resonance spectra at 15 K of reduced membrane particles of Paracoccus denitrificans exhibit resonance signals with g values, line shapes and temperature profile which are similar to the signals of the iron-sulfur centers observed in the NADH-ubiquinone segment of mitochondrial respiratory chains. These iron-sulfur centers are reducible with NADH, NADPH as well as chemically with dithionite. 2. Sulphate-limited growth of Paracoccus denitrificans results in the loss of an electron paramagnetic resonance signal (gz approximately 2.05, gy approximately gx approximately 1.92) which has properties similar to those of iron-sulfur center 2 of the NADH dehydrogenase of mitochondrial origin. The loss of this signal is accompanied by a decrease in the NADH oxidase and NADH ferricyanide oxidoreductase activities to respectively 30 and 40% of the values found for succinate-limited growth conditions. In addition respiration in membrane particles from sulphate-limited cells loses its sensitivity to rotenone. 3. Since sulphate-limited growth of Paracoccus denitrificans induces loss of site I phosphorylation [Arch. Microbiol. (1977) 112, 25-34] these observations suggest a close correlation between site I phosphorylation, rotenone-sensitivity and the presence of an electron paramagnetic resonance signal with gz approximately 2.05 and gy approximately gx approximately 1.92.
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PMID:The role of iron-sulfur center 2 in electron transport and energy conservation in the NADH-ubiquinone segment of the respiratory chain in Paracoccus denitrificans. 20 53

Oxidation of exogenous NADH in mitochondria isolated from wild type and mi-1 mutant of Neurospora crassa decreases rapidly in vitro. In mi-1 mutant mitochondria the inactivation concerns the alternate pathway of oxidation whereas in the wild type it involves an unknown component of the respiratory chain. The activity of the primary NADH dehydrogenase is constant within the time of the experiments (2-4 h). NADH oxidase is not inactivated if oxygen is removed from the incubation medium by nitrogen bubbling. Succinate oxidase does not show any remarkable changes in activity within 2-3 h. In fresh mitochondria of the mi-1 mutant reduced ubiquinone is completely reoxidized by cytochrome oxidase but only 80% reoxidized by the alternate oxidase. In aged mitochondria of the mi-1 mutant in the presence of cyanide, ubiquinone is reduced to the level characteristic for fresh mitochondria in which respiration is completely inhibited by cyanide plus salicylhydroxamic acid. In these mitochondria the reoxidation of the reduced ubiquinone proceeds only via the cytochrome pathway. It is supposed that a labile component(s) of the respiratory chain present in the mi-1 mutant and the wild type mitochondria may, in mi-1 mutant, act as an alternate oxidase.
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PMID:Disappearance of the cyanide-insensitive pathway of oxidation in mitochondria of MI-1 mutant of Neurospora crassa in vitro. 20 34

The isolated NADH-ubiquinone oxidoreductase complex of bovine heart mitochondria reduces ubiquinone analogues by two pathways. One pathway is inhibited by rotenone, and reduction of quinones takes place in the lipid phase of the system. The other pathway is insensitive to rotenone and reduction takes place in the aqueous phase. The variation of rates of electron transpport with the chemical nature of the quinone analogue and the concentrations of both quinone and phospholipid can be rationalized in terms of partition of the quinone between the aqueous and lipid phases of the system. Thus one function of phospholipid associated with the enzyme appears to be to act as solvent for ubiquinone reduced by the rotenone-sensitive pathway. This proposal is supported by the kinetic behaviour of enzyme whose endogenous lipids have been replaced by (1,2)-dimyristoylsn-glycero-3-phosphocholine. Thus, under certain circumstances, the rotenone-sensitive reduction of ubiquinone-1 exhibited a substantial increase in activation energy below the phase-transition temperature of the synthetic lipid, whereas the reduction of other acceptors was unaffected.
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PMID:The role of phospholipids in the reduction of ubiquinone analogues by the mitochondrial reduced nicotinamide-adenine dinucleotide-ubiquinone oxidoreductase complex. 21 Jul 62

1. The NADH-ubiquinone oxidoreductase complex (Complex I) and the ubiquinol-cytochrome c oxidoreductase complex (Complex III) combine in a 1:1 molar ratio to give NADH-cytochrome c oxidoreductase (Complex I-Complex III). 2. Experiments on the inhibition of the NADH-cytochrome c oxidoreductase activity of mixtures of Complexes I and III by rotenone and antimycin indicate that electron transfer between a unit of Complex I-Complex III and extra molecules of Complexes I or III does not contribute to the overall rate of cytochrome c reduction. 3. The reduction by NADH of the cytochrome b of mixtures of Complexes I and III is biphasic. The extents of the fast and slow phases of reduction are determined by the proportion of the total Complex III specifically associated with Complex I. 4. Activation-energy measurements suggest that the structural features of the Complex I-Complex III unit promote oxidoreduction of endogenous ubiquinone-10.
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PMID:The interaction between mitochondrial NADH-ubiquinone oxidoreductase and ubiquinol-cytochrome c oxidoreductase. Evidence for stoicheiometric association. 21 22

In Rhodopseudomonas sphaeroides chromatophores there are 25 +/- 3 ubiquinone (Q) molecules/reaction center protein. They comprise several thermodynamically and functionally different ubiquinone complements. There are approx. 19 ubiquinones (Em7 = 90 mV) in the main ubiquinone complement which, within experimental resolution, appears thermodynamically homogenous and follows the redox reaction Q + 2e + 2H+ in equilibrium with QH2 from pH 5--9. A method which takes advantage of the 2H+ bound/molecule of Q reduced is described for measuring the time course of light-activated reaction center-driven reduction and oxidation of the 19 Q complement. No stable semiquinones were detected in the constitutents of the 19 Q complement. There are approx. 6 ubiquinones of lower Em which are currently unaccounted for, although one or possibly two of these can be assigned to the quinones of the reaction center protein. The remainder may be associated with the NADH-ubiquinone oxidoreductase.
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PMID:Ubiquinone in Rhodopseudomonas sphaeroides. Some thermodynamic properties. 22 Oct 12

The electron transfer complexes, succinate: ubiquinone reductase, ubiquinone: cytochrome c reductase, and cytochrome c: O2 oxidase were isolated from the mitochondrial membranes of Neurospora crassa by the following steps. Modification of the contents of the complexes in mitochondria by growing cells on chloramphenicol; solubilisation of the complexes by Triton X-100; affinity chromatography on immobilized cytochrome c and ion exchange and gel chromatography. Ubiquinone reductase was obtained in a monomeric form (Mr approximately 130 000) consisting of a flavin subunit (Mr 72 000) an iron-sulfur subunit (Mr 28 000) and a cytochrome b subunit (Mr probably 14 000). Cytochrome c reductase was obtained in a dimeric form (Mr approximately 550 000), the monomeric unit comprising the cytochromes b (Mr each 30 000), a cytochrome c1 (Mr 31 000), the iron-sulfur subunit (Mr 25 000), and six subunits without known prosthetic groups (Mr 9000, 11 000, 14 000, 45 000, 45 000, and 52 000). Cytochrome c oxidase was also isolated in a dimeric form (Mr approximately 320 000) comprising two copies each of seven subunits (Mr 9000, 12 000, 14 000, 18 000, 21 000, 29 000, and 40 000). The complexes were essentially free of phospholipid. Each bound one micelle of Triton X-100 (Mr approximately 90 000). After isolation, the bound Triton X-100 could be replaced by other nonionic detergents such as: alkylphenyl polyoxyethylene ethers, alkyl polyoxyethylene ethers and acyl polyoxyethylene sorbitan esters.
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PMID:Isolation of mitochondrial succinate: ubiquinone reductase, cytochrome c reductase and cytochrome c oxidase from Neurospora crassa using nonionic detergent. 22 65

The enzymology of isolated succinate: ubiquinone reductase and ubiquinone: cytochrome c reductase in nonionic detergents (alkyl polyoxyethylene derivatives) was studied. In the membrane the two multiprotein complexes and their hydrophobic substrates ubiquinone and dihydroubiquinone, are embedded in a common lipid bilayer. In detergent solutions the complexes are each inserted into micelles. Detergent micelles also serve as a solvent for the complexes hydrophobic substrates. As a consequence the isolated complexes are in a discontinuous phase with respect to their hydrophobic substrates and with respect to each other. Three types of assays were used. Firstly, single enzyme assays in which the hydrophobic substrates had to transfer from free micelles to the complex-bound micelles in order for enzyme reactions to occur. Secondly, assays in which the enzymic reactions were coupled to auxiliary nonenzymic reactions which rapidly converted the hydrophobic products back into substrates within the complex-bound micelle. Dichloroindophenol was used for the oxidation of dihydroubiquinone and dihydroduroquinone for the reduction of ubiquinone. Thirdly, assays in which the succinate: ubiquinone reductase reaction was coupled with the ubiquinone: cytochrome c reductase reaction. With the first type of assay, the kinetics of the substrate transfer reaction was dependent upon the type of detergent. In detergents with small polyoxyethylene head groups the transfer reactions were rate-limiting, and in detergents with large polyoxyethylene head groups the transfer reactions were fast and the enzymic reactions were rate-limiting...
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PMID:Enzymology of ubiquinone-utilizing electron transfer complexes in nonionic detergent. 22 66

1. Incubation of NADH-ubiquinone oxidoreductase (Complex I) with chymotrypsin caused loss of rotenone-sensitive ubiquinone-1 reduction and an increase in rotenone-insensitive ubiquinone reduction. 2. Within the same time-course, NADH-K(3)Fe(CN)(6) oxidoreductase activity was unaffected. 3. Mixing of chymotrypsin-treated Complex I with Complex III did not give rise to NADH-cytochrome c oxidoreductase activity. 4. Gel electrophoresis in the presence of sodium dodecyl sulphate revealed selective degradation of several constituent polypeptides by chymotrypsin. 5. With higher chymotrypsin concentrations and longer incubation times, a decrease in NADH-K(3)Fe(CN)(6) oxidoreductase was observed. The kinetics of this decrease correlated with solubilization of the low-molecular-weight type-II NADH dehydrogenase (subunit mol.wts. 53000 and 27000) and with degradation of a polypeptide of mol.wt. 30000. 6. Phospholipid-depleted Complex I was more rapidly degraded by chymotrypsin. Specifically, a subunit of mol.wt. 75000, resistant to chymotrypsin in untreated Complex I, was degraded in phospholipid-depleted Complex I. In addition, the 30000-mol.wt. polypeptide was also more rapidly digested, correlating with an increased rate of transformation to type II NADH dehydrogenase.
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PMID:Effects of proteolytic digestion by chymotrypsin on the structure and catalytic properties of reduced nicotinamide-adenine dinucleotide-ubiquinone oxidoreductase from bovine heart mitochondria. 41 83

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


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