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Results for “Electron Transport Complex IV”

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At least 19 recordsLinked to original sources
PubMed1995

L-dopa inhibits complex IV of the electron transport chain in catecholamine-rich human neuroblastoma NB69 cells.

L-3,4-Dihydroxyphenylalanine (L-dopa) is toxic for human neuroblastoma cells NB69 and its toxicity is related to several mechanisms including quinone formation and enhanced production of free radicals related to the metabolism of dopamine via monoamine oxidase type B. We studied the effect of L-DOPA on activities of enzyme complexes in the electron transport chain (ETC) in homogenate preparations from the human neuroblastoma cell line NB69. As a preliminary step we compared the activity of ETC in cellular homogenates with that of purified mitochondria from NB69 cells and rat brain. Specific activities for complex I, complex II-III, and complex IV in NB69 cells were, respectively, 65, 96, and 32% of those in brain mitochondria. Complex I activity was inhibited in a dose-dependent way by 1-methyl-4-phenylpyridinium ion with an EC50 of approximately 150 microM. Treatment with 0.25 mM L-dopa for 5 days reduces complex IV activity to 74% of control values but does not change either complex I or citrate synthase. Ascorbic acid (1 mM), which protects NB69 cells from L-dopa-induced neurotoxicity, increases complex IV activity to 133% of the control and does not change other ETC complexes. Ascorbic acid also reverses L-dopa-induced reduction of complex IV activity in NB69 cells. This observation might indicate that the protection observed with ascorbic acid is related to complex IV activation. In vitro incubation with L-dopa (0.125-4 mM) for 2 min produced a dose-dependent reduction of complex IV without change in complex I and II-III activities.

1-Methyl-4-phenylpyridinium↗
PubMed1996

Regulation of the H+/e- stoichiometry of cytochrome c oxidase from bovine heart by intramitochondrial ATP/ADP ratios.

This paper describes the effect of intramitochondrial ATP/ADP ratios on the H+/e- stoichiometry of reconstituted cytochrome c oxidase (COX) from bovine heart. At 100% intraliposomal ATP the H+/e- stoichiometry of the reconstituted enzyme is decreased to half of the value measured below 98% intraliposomal ATP (above 2% ADP), while it remains constant up to 100% ADP. The decrease is obtained with different COX preparations, independent of the absolute value of the H+/e- stoichiometry. Decrease of H+/e- stoichiometry is prevented by preincubation of the enzyme with a tissue-specific monoclonal antibody to subunit VIa-H (heart type). Tissue-specific regulation of the efficiency of energy transduction in COX of muscle mitochondria could have a physiological function in maintaining the body temperature at rest or sleep, i.e. at low ATP expenditure.

Adenosine Diphosphate↗
PubMed2005

A role for the protein in internal electron transfer to the catalytic center of cytochrome c oxidase.

Internal electron transfer (ET) to heme a(3) during anaerobic reduction of oxidized bovine heart cytochrome c oxidase (CcO) was studied under conditions where heme a and Cu(A) were fully reduced by excess hexaamineruthenium. The data show that ET to heme a(3) is controlled by the state of ionization of a single protolytic residue with a pK(a) of 6.5 +/- 0.2. On the basis of the view that ET to the catalytic site is limited by coupled proton transfer, this pK(a) was attributed to Glu60 which is located at the entrance of the proton-conducting K channel on the matrix side of CcO. It is proposed that Glu60 controls proton entry into the channel. However, even with this channel open, there is the second factor that regulates ET, and this is ascribed to the rate of proton diffusion in the channel. In addition, it is concluded that proton transfer in the K channel is reversibly inhibited by the detergent Triton X-100. It is also found that the rate of ET to heme a(3) in the as-isolated resting enzyme and in CcO "activated" by reaction of fully reduced enzyme with O(2) is the same, implying that the catalytic sites of these two forms of oxidized enzyme are essentially identical.

Animals↗
PubMed2005

The iron-sulfur cluster of the Rieske iron-sulfur protein functions as a proton-exiting gate in the cytochrome bc(1) complex.

The destruction of the Rieske iron-sulfur cluster ([2Fe-2S]) in the bc(1) complex by hematoporphyrin-promoted photoinactivation resulted in the complex becoming proton-permeable. To study further the role of this [2Fe-2S] cluster in proton translocation of the bc(1) complex, Rhodobacter sphaeroides mutants expressing His-tagged cytochrome bc(1) complexes with mutations at the histidine ligands of the [2Fe-2S] cluster were generated and characterized. These mutants lacked the [2Fe-2S] cluster and possessed no bc(1) activity. When the mutant complex was co-inlaid in phospholipid vesicles with intact bovine mitochondrial bc(1) complex or cytochrome c oxidase, the proton ejection, normally observed in intact reductase or oxidase vesicles during the oxidation of their corresponding substrates, disappeared. This indicated the creation of a proton-leaking channel in the mutant complex, whose [2Fe-2S] cluster was lacking. Insertion of the bc(1) complex lacking the head domain of the Rieske iron-sulfur protein, removed by thermolysin digestion, into PL vesicles together with mitochondrial bc(1) complex also rendered the vesicles proton-permeable. Addition of the excess purified head domain of the Rieske iron-sulfur protein partially restored the proton-pumping activity. These results indicated that elimination of the [2Fe-2S] cluster in mutant bc(1) complexes opened up an otherwise closed proton channel within the bc(1) complex. It was speculated that in the normal catalytic cycle of the bc(1) complex, the [2Fe-2S] cluster may function as a proton-exiting gate.

Animals↗
PubMed1964

PORCINE CONTAGIOUS PLEUROPNEUMONIA. 3. INTERRELATIONSHIP OF HEMOPHILUS PLEUROPNEUMONIAE TO OTHER SPECIES OF HEMOPHILUS: NUTRITIONAL, METABOLIC, TRANSFORMATION, AND ELECTRON MICROSCOPY STUDIES.

Hemophilus pleuropneumoniae, the causative agent of porcine contagious pleuropneumonia (PCP) is an encapsulated organism that has the metabolic features of the parainfluenza group of Hemophilus in that it requires DPN but not hemin for growth. Its formation of nitrate reductase cytochrome a(1) and non-physiologically reducible cytochrome c(1) in the stationary phase, together with its requirement of electron transport through oxidases for growth are typical of non-hemin-requiring Hemophilus species. It has the closest genetic homology, judged from the capacity of its DNA to induce transformation to streptomycin resistance, with H. parasuis but can be differentiated from this organism on the basis of its growth in defined medium and its marked and characteristic pathogenicity for swine.

Actinobacillus pleuropneumoniae↗
PubMed2005

Wedding biodiversity inventory of a large and complex Lepidoptera fauna with DNA barcoding.

By facilitating bioliteracy, DNA barcoding has the potential to improve the way the world relates to wild biodiversity. Here we describe the early stages of the use of cox1 barcoding to supplement and strengthen the taxonomic platform underpinning the inventory of thousands of sympatric species of caterpillars in tropical dry forest, cloud forest and rain forest in northwestern Costa Rica. The results show that barcoding a biologically complex biota unambiguously distinguishes among 97% of more than 1000 species of reared Lepidoptera. Those few species whose barcodes overlap are closely related and not confused with other species. Barcoding also has revealed a substantial number of cryptic species among morphologically defined species, associated sexes, and reinforced identification of species that are difficult to distinguish morphologically. For barcoding to achieve its full potential, (i) ability to rapidly and cheaply barcode older museum specimens is urgent, (ii) museums need to address the opportunity and responsibility for housing large numbers of barcode voucher specimens, (iii) substantial resources need be mustered to support the taxonomic side of the partnership with barcoding, and (iv) hand-held field-friendly barcorder must emerge as a mutualism with the taxasphere and the barcoding initiative, in a manner such that its use generates a resource base for the taxonomic process as well as a tool for the user.

Animals↗
PubMed2006

Spectral and kinetic equivalence of oxidized cytochrome C oxidase as isolated and "activated" by reoxidation.

The spectral and kinetic characteristics of two oxidized states of bovine heart cytochrome c oxidase (CcO) have been compared. The first is the oxidized state of enzyme isolated in the fast form (O) and the second is the form that is obtained immediately after oxidation of fully reduced CcO with O2 (OH). No observable differences were found between O and OH states in: (i) the rate of anaerobic reduction of heme a3 for both the detergent-solubilized enzyme and for enzyme embedded in its natural membraneous environment, (ii) the one-electron distribution between heme a3 and CuB in the course of the full anaerobic reduction, (iii) the optical and (iv) EPR spectra. Within experimental error of these characteristics both forms are identical. Based on these observations it is concluded that the reduction potentials and the ligation states of heme a3 and CuB are the same for CcO in the O and OH states.

Animals↗
PubMed2004

Supramolecular organization of cytochrome c oxidase- and alternative oxidase-dependent respiratory chains in the filamentous fungus Podospora anserina.

To elucidate the molecular basis of the link between respiration and longevity, we have studied the organization of the respiratory chain of a wild-type strain and of two long-lived mutants of the filamentous fungus Podospora anserina. This established aging model is able to respire by either the standard or the alternative pathway. In the latter pathway, electrons are directly transferred from ubiquinol to the alternative oxidase and thus bypass complexes III and IV. We show that the cytochrome c oxidase pathway is organized according to the mammalian "respirasome" model (Schägger, H., and Pfeiffer, K. (2000) EMBO J. 19, 1777-1783). In contrast, the alternative pathway is composed of distinct supercomplexes of complexes I and III (i.e. I(2) and I(2)III(2)), which have not been described so far. Enzymatic analysis reveals distinct functional properties of complexes I and III belonging to either cytochrome c oxidase- or alternative oxidase-dependent pathways. By a gentle colorless-native PAGE, almost all of the ATP synthases from mitochondria respiring by either pathway were preserved in the dimeric state. Our data are of significance for the understanding of both respiratory pathways as well as lifespan control and aging.

Ascomycota↗
PubMed1965

ACRIFLAVINE INDUCTION OF DIFFERENT KINDS OF "PETITE" MITOCHONDRIAL POPULATIONS IN SACCHAROMYCES CEREVISIAE.

Avers, Charlotte J. (Rutgers, The State University, New Brunswick, N. J.), Cynthia R. Pfeffer, and Martha W. Rancourt. Acriflavine induction of different kinds of "petite" mitochondrial populations in Saccharomyces cerevisiae. J. Bacteriol. 90:481-494. 1965.-Mutant frequencies induced by 1 or 2 hr in 16 and 64 mug/ml of acriflavine were significantly higher during acceleration and log-phase exposures than during lag or stationary phases. From these induced petites, 59 colonies were selected at random and established in pure culture. All strains were analyzed histochemically for mitochondrial cytochrome oxidase and succinic dehydrogenase (SDH) reactions. On the basis of counts of stained mitochondria per cell obtained by light microscopy, four different cell phenotypes were recognized among the mutant strains: (i) reduced cytochrome oxidase, wild-type SDH; (ii) reduced cytochrome oxidase, high SDH; (iii) absent cytochrome oxidase, high SDH; and (iv) absent cytochrome oxidase, wild-type SDH. The last group was the most common, characterizing 43 of the 59 strains. Electron microscopy showed differences in mitochondrial ultrastructure for the various cell phenotype classes. Electron histochemical localizations showed cytochrome oxidase reaction product only on mitochondrial membranes of respiration-competent cells. Both reactive and unreactive mitochondria occurred in the same cell in mutants with partial respiratory competence. Different mitochondrial subpopulation mixtures characterized the mutant strains, many of which had at least two kinds of respiratory-competent types per chondriome. The diverse chondriomes comprised a stable feature of the mutants, since they have been maintained unchanged during serial transfer for more than 1 year in culture. Together with earlier reports of at least two kinds of mitochondria in wild-type cells, the evidence indicated that mitochondria were capable of regulating some portion of their phenotype. The recognition of mitochondrial phenotypes was proposed as an initial step in a formal analysis of organelle heredity.

Acridines↗