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D Zannoni

Publications and source records attributed to D Zannoni.

At least 37 records · Page 2Linked to original sources
PubMed1992

Oxidation of External NAD(P)H by Jerusalem Artichoke (Helianthus tuberosus) Mitochondria : A Kinetic and Inhibitor Study.

The functional interaction between the externally located NAD(P)H dehydrogenase and the Q-pool acceptor site(s) in Percoll-purified mitochondria from Jerusalem artichoke (Helianthus tuberosus L. cv OB1) mitochondria has been investigated. Oxidation of exogenous NADH is stimulated by ubiquinone (UQ(1)) with a parallel decrease of the apparent K(m) for NADH. In the presence of saturating amounts of UQ(1) as electron acceptor, the K(m) (NADH) is not affected by variations of the ionic strength. Conversely, the K(m) for UQ(1) is decreased by the screening effect of negative charges on the outer membrane surface. Under low-ionic strength, the hydroxyflavone platanetin progressively inhibits NADH oxidation with a mean inhibition dose of approximately 3 nanomoles of inhibitor per milligram of protein. Interestingly, under high-ionic strength, oxidation of NADH proceeds through two platanetin binding sites, one of which has a lower affinity for the inhibitor (mean inhibition dose = 20 nanomoles per milligram protein), because it is located near the outer surface of the membrane. This latter site is the one involved in the oxidation of external NADPH and, possibly, also affected by spermine and spermidine. Similarly to NADH, oxidation of NADPH is fully sensitive to micromolar concentrations of free Ca(2+) ions; in addition, similar concentrations of the sulfhydryl reagent mersalyl are required to inhibit both NADH and NADPH oxidative activities. The results are interpreted as evidence for the presence of a single nonspecific NAD(P)H dehydrogenase.

Journal Article↗
PubMed1991

Temperature dependence of charge recombination from the P+QA- and P+QB- states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus.

The temperature dependence of charge recombination from the P+QA- and from the P+QB- states produced by a flash was studied in reaction centers isolated from the photosynthetic thermophilic bacterium Chloroflexus aurantiacus. P designates the primary electron donor; QA and QB the primary and secondary quinone electron acceptors respectively. In QB-depleted reaction centers the rate constant (kAP) for P+QA- recombination was temperature independent between 0-50 degrees C (17.6 +/- 0.7 s-1 at pH 8 and pH 10). The same value was obtained in intact membranes in the presence of o-phenanthroline. Upon lowering the temperature from 250 K to 160 K, kAP increased by a factor of two and remained constant down to 80 K. The overall temperature dependence of kAP was consistent with an activationless process. Ubiquinone (UQ-3) and different types of menaquinone were used for QB reconstitution. In UQ-3 reconstituted reaction centers charge recombination was monoexponential (rate constant k = 0.18 +/- 0.03 s-1) and temperature independent between 5-40 degrees C. In contrast, in menaquinone-3- and menaquinone-4-reconstituted reaction centers P+ rereduction following a flash was markedly biphasic and temperature dependent. In menaquinone-6-reconstituted reaction centers a minor contribution from a third kinetic phase corresponding to P+QA- charge recombination was detected. Analysis of these kinetics and of the effects of the inhibitor o-phenanthroline at high temperature suggest that in detergent suspensions of menaquinone-reconstituted reaction centers a redox reaction removing electrons from the quinone acceptor complex competes with charge recombination. Instability of the semiquinone anions is more pronounced when QB is a short-chain menaquinone. From the temperature dependence of P+ decay the activation parameters for the P+QB- recombination and for the competing side oxidation of the reduced menaquinone acceptor have been derived. For both reactions the activation enthalpies and entropies change markedly with menaquinone chain length but counterbalance each other, resulting in activation free energies at ambient temperature independent of the menaquinone tail. When reaction centers are incorporated into phospholipid vesicles containing menaquinone-8 a temperature-dependent, monophasic, o-phenanthroline-sensitive recombination from the P+QB- state is observed, which is consistent with the formation of stable semiquinone anions. This result seems to indicate a proper QB functioning in the two-subunit reaction center isolated from Chlorflexus aurantiacus when the complex is inserted into a lipid bilayer.

Bacteria↗
PubMed1991

Membrane-bound cytochromes in Chloroflexus aurantiacus studied by EPR.

The heme components of chlorosome-depleted membranes of the green-gliding bacterium Chloroflexus aurantiacus were studied by EPR spectroscopy. The four major species, which are present in approximately equimolar quantities, are characterized by the following gz values, redox midpoint potentials and orientations of heme planes with respect to the plane of the membrane: gz = 3.40, Em = +280 mV, 30 degrees; gz = 3.33, Em = 0 mV, 45 degrees; gz = 3.03, Em = +95 mV, 40-50 degrees and gz = 2.95, Em = +150 mV, 90 degrees. These four hemes were attributed to cytochrome c554, the membrane-bound immediate electron donor to the photosynthetic reaction centre in Chloroflexus. All hemes except that with the highest potential were able to undergo photooxidation at 4 K. The photooxidation of the lowest potential heme was stable, whereas that of the +95 mV and the +150 mV hemes reversed on increasing the temperature to 100 K in darkness, due to charge recombination. The ability to photooxidize these hemes at 4 K was lost upon aging of samples. The results demonstrate that a reaction-centre-associated tetraheme cytochrome subunit, analogous to that of purple bacteria, is also present in C. aurantiacus.

Bacteria↗
PubMed1991

Effects of Polyamines on the Oxidation of Exogenous NADH by Jerusalem Artichoke (Helianthus tuberosus) Mitochondria.

The effect of polyamines (putrescine, spermine, and spermidine) on the oxidation of exogenous NADH by Jerusalem artichoke (Helianthus tuberosus L. cv. OB1) mitochondria, have been studied. Addition of spermine and/or spermidine to a suspension of mitochondria in a low-cation medium (2 millimolar-K(+)) caused a decrease in the apparent K(m) and an increase in the apparent V(max) for the oxidation of exogenous NADH. These polycations released by screening effect the mitochondrially induced quenching of 9-aminoacridine fluorescence, their efficiency being dependent on the valency of the cation (C(4+) > C(3+)). Conversely, putrescine only slightly affected both kinetic parameters of exogenous NADH oxidation and the number of fixed charges on the membranes. Spermine and spermidine, but not putrescine, decreased the apparent K(m) for Ca(2+) from about 1 to about 0.2 micromolar, required to activate external NADH oxidation in a high-cation medium, containing physiological concentrations of Pi, Mg(2+) and K(+). The results are interpreted as evidence for a role of spermine and spermidine in the modulation of exogenous NADH oxidation by plant mitochondria in vivo.

Journal Article↗
PubMed1990

Measurement of the redox state of the ubiquinone pool in Rhodobacter capsulatus membrane fragments.

The dependence of the respiratory rate on the redox poise of the quinone pool was investigated in wild type and mutant membranes of Rhodobacter capsulatus. A linear relationship has been found between these two parameters only when succinate was oxidized by the bc1 complex. Conversely, a marked nonlinear relationship was observed between the Q-pool reduction level and the respiratory rate when O2 uptake occurred via the alternative oxidase. In addition, it was found that this latter pathway was not engaged until Q-pool reduction level reached approximately 25%. These results are discussed within the framework of a homogeneous pool regulating both photosynthetic and respiratory fluxes.

Cytochromes c1↗
PubMed1990

Spermidine Uptake by Mitochondria of Helianthus tuberosus.

In the present work evidence is provided that spermidine, a polyamine largely present in plant tissues, may be transported, at physiological concentrations, into the matrix space of mitochondria isolated from tubers of Helianthus tuberosus L. cv OB1 (Jerusalem artichoke). It is concluded that the movement of spermidine strictly depends on membrane potential, since it is drastically blocked by valinomycin and only slightly sensitive to nigericin. Mg(2+) and K(+) inhibit the transport of spermidine in line with the general concept that these cations compete for the same binding sites on the mitochondrial membrane. In contrast to previous data on mammalian mitochondria, spermidine uptake by plant mitochondria does not depend on the presence of inorganic phosphate. This latter result, along with evidence that Ca(2+) does not affect accumulation of spermidine, indicates that the control of the polyamine uptake mechanism in plant mitochondria is distinct from that of mammalian systems.

Journal Article↗
PubMed1988

Oxidation-reduction thermodynamics of the acceptor quinone complex in whole-membrane fragments from Chloroflexus aurantiacus.

Oxidation-reduction thermodynamic equilibria involving the quinone-acceptor complex have been examined in whole-membrane fragments from Chloroflexus aurantiacus. The primary quinone acceptor was titrated by monitoring the amount of cytochrome c554 photooxidized by a flash of light as a function of the redox potential. In contrast to previous data obtained in purified plasma membranes, in which the primary quinone acceptor exhibited a midpoint potential equal to -50 mV at pH 8.2, in whole-membrane fragments it titrated at -210 mV (pH 8.0), with a pH dependence of -60 mV/pH up to a pK value of 9.3. o-Phenanthroline, an inhibitor of electron transfer from the primary to the secondary quinone acceptor, shifted the Em/pH curve of the primary acceptor to higher redox potentials. The midpoint potential of the secondary quinone acceptor and its dependence on pH has been determined by comparing the kinetics of the charge recombination processes within the reaction center complex in the presence and in the absence of o-phenanthroline. It is concluded that both the primary and the secondary quinone acceptors interact with a proton, with pK values of 9.3 and of approximately 10.2 respectively. At physiological pH the electron appears to be stabilized on the secondary with respect to the primary quinone acceptor by approximately 60 meV.

Bacteria↗
PubMed1986

Effect of oxygen limitation on the formation of the electron transport system of the phytopathogenic fluorescent bacterium Pseudomonas cichorii.

The composition of the membrane-bound electron transport system of the phytopathogenic bacterium Pseudomonas cichorii underwent modification in response to oxygen supply. Growth adaptation to low oxygen concentrations was characterized by repression of cytochromes involved in ubiquinol-cyt. c oxidoreductase and cyt. c oxidase activities. By contrast, cyto. o, i.e., the alternative cyanide-insensitive oxidase of P. cichorii, was unaffected by low oxygen tension. No a-type cytochromes could be detected at any stage of growth.

Cytochrome b Group↗
PubMed1985

Effects of myxothiazol and 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole on the respiratory pathways of the phytopathogenic fluorescent bacteria Pseudomonas cichorii and Pseudomonas aptata.

Myxothiazol inhibited the electron transport in the cytochrome b/c segment of membrane particles from Pseudomonas cichorii. A residual NADH-oxidation due to the presence of an alternative pathway via cytochrome o (Em, 7 = +250 mV) was sensitive to the quinone analog 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT). This latter inhibitor was equally effective in blocking the linear respiratory chain of Pseudomonas aptata, a strain deficient in cytochromes of c type and Rieske iron-sulphur centre. The analysis of the oxido-reduction kinetic patterns of cytochromes indicated that, among the b type haems present in P. aptata, only cyt. o could be reduced by ubiquinol-1 in a reaction insensitive to both antimycin A and myxothiazol but inhibited by UHDBT. This latter finding has been correlated to the fact that P. aptata exhibits a defective b/c complex. In membranes from P. cichorii, in which the absorption maximum of dithionite reduced cytochrome(s) b shifted by 2-3 nm in the presence of antimycin A and/or myxothiazol, the electron flow through the b/c oxidoreductase complex has tentatively been arranged in a proton motive "Q-cycle" like mechanism.

Antifungal Agents↗
PubMed1985

Functional Characterization and Partial Purification of the Ubiquinol-Cytochrome c Oxidoreductase from Higher Plant Mitochondria (Helianthus tuberosus).

The functional and thermodynamic characteristics of the ubiquinolcytochrome (Cyt) c oxidoreductase in a Cyt b/c(1)-enriched fraction (defined S-1) isolated from Jerusalem artichoke mitochondria (JAM) (Helianthus tuberosus), have been analyzed. Fraction S-1, obtained through deoxycholate-KCl fractionation procedure, contained one Cyt of c type (formally c(1) with Em(7.0) of +240 millivolts), two b type Cyt with Em(7.0) values of +100 and -25 millivolts, ferredoxin-like centers presumably linked to succinic- and NADH-dehydrogenases, and a Rieske-type iron sulfur center (g(y) = 1.89). The ubiquinol-dependent Cyt c reduction by fraction S-1 showed sensitivity to antimycin A, myxothiazol, and n-2-hepthyl-1-hydroxyquinoline N-oxide with I(50) of 12 nanomolar, 30 nanomolar, and 0.1 micromolar, respectively. Oxidation-induced extra b type reduction, a widespread phenomenon of bacterial and mitochondrial respiratory systems, has also been observed in both intact mitochondria and S-1 fraction. The data seem to blur previous experiments in which both spectral and functional differences between higher plant and mammalian mitochondria have been underlined.

Journal Article↗
PubMed1983

Oxygen-induced inhibition of light-dependent uptake of tetraphenylphosphonium ions as a probe of a direct interaction between photosynthetic and respiratory components in cells of Rhodopseudomonas capsulata.

Light-generated and oxygen-dependent membrane potentials by heterotrophycally grown cells of Rhodopseudomonas capsulata have been investigated by using a tetraphenylphosphonium ion-selective electrode. The results show that respiratory electron transport affects the magnitude of photogenerated membrane potential while photosynthesis seems to either inhibit or stimulate respiration in coupled or uncoupled cells, respectively. These observations have been considered as evidence that the intracytoplasmic membrane system of R. capsulata contain respiratory and photosynthetic apparatuses which are strictly intermingled.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1980

Spectral and functional comparisons between the carotenoids of the two antenna complexes of Rhodopseudomonas capsulata.

The spectral and functional properties of carotenoids associated with each of the two light-harvesting complexes of the Rhodopseudomonas capsulata photosynthetic antenna system have been distinguished by studying mutants lacking one or the other complex. In mutants containing only the light-harvesting I complex (LH-I), the absorption spectrum of the carotenoids is blue-shifted compared to wild type. Carotenoid absorption in mutants possessing only the light-harvesting II complex (LH-II) complex is red-shifted. The circular dichroism spectrum of carotenoids in each complex is also distinctive. Although carotenoids in each complex function with approximately the same efficiency in harvesting and transmitting light energy for photosynthesis, only the carotenoids associated with LH-II undergo an electrochromic bandshift upon generation of a transmembrane potential. These observations are interpreted to indicate that both the orientation of carotenoid molecules with respect to the plane of the membrane, and the immediate electrochemical environment of these molecules differ in the two light-harvesting complexes.

Bacterial Chromatophores↗
PubMed1978

[Current potential of fiberscopy in the diagnosis of bronchopulmonary lesions].

The Authors relate the results of their casuistics of bronchial endoscopies. Out of 3438 endoscopies, 1237 were bronchial biopsies and 496 lung biopsies. According to the results obtained the Authors have concluded that this method represents an important progress in thoracic endoscopy. It can be also widely applied for the diagnosis of bronchopulmonary diseases.

Biopsy↗
PubMed1976

Energy tranduction in photosynthetic bacteria. XI. Further resolution of cytochromes of b type and the nature of the co-sensitive oxidase present in the respiratory chain of Rhodopseudomonas capsulata.

1. In membranes prepared from dark grown cells of Rhodopseudomonas capsulata, five cytochromes of b type (E'0 at pH 7.0 +413+/-5, +270+/-5, +148+/-5, +56+/-5 and -32+/-5 mV) can be detected by redox titrations at different pH values. The midpoint potentials of only three of these cytochromes (b148, b56, and b-32) vary as a function of pH with a slope of 30 mV per pH unit. 2. In the presence of a CO/N2 mixture, the apparent E'0 of cytochrome b270 shifts markedly towards higher potentials (+355mV); a similar but less pronounced shift is apparent also for cytochrome b150. The effect of CO on the midpoint potential of cytochrome b270 is absent in the respiration deficient mutant M6 which possesses a specific lesion in the CO-sensitive segment of the branched respiratory chain present in the wild type strain. 3. Preparations of spheroplasts with lysozyme digestion lead to the release of a large amount of cytochrome c2 and of virtually all cytochrome cc'. These preparations show a respiratory chain impaired in the electron pathway sensitive to low KCN concentration, in agreement with the proposed role of cytochrome c2 in this branch; on the contrary, the activity of the CO-sensitive branch remains unaffected, indicating that neither cytochrome c2 nor the CO-binding cytochrome cc' are involved in this pathway. 4. Membranes prepared from spheroplasts still possess a CO-binding pigment characterized by maxima at 420.5, 543 and 574 nm and minima at 431, 560 nm in C0-difference spectra and with an alpha band at 562.5 nm in reduced minus oxidized difference spectra. This membrane-bound cytochrome, which is coincident with cytochrome b270, can be classified as a typical cytochrome "0" and considered the alternative CO-sensitive oxidase.

Anaerobiosis↗