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G F Azzone

Publications and source records attributed to G F Azzone.

At least 73 records · Page 4Linked to original sources
PubMed1981

Cytochrome c as an electron shuttle between the outer and inner mitochondrial membranes.

Addition of exogenous NADH to rotenone- and antimycin A-treated mitochondria, in 125 mM KCl, results in rates of oxygen uptake of 0.5-1 and 10-12 nanoatoms of oxygen X mg protein-1 X min-1 in the absence and presence of cytochrome c, respectively. During oxidation of exogenous NADH there is a fast and complete reduction of cytochrome b5 while endogenous or added exogenous cytochrome c become 10-15% and 100% reduced, respectively. The reoxidation of cytochrome b5, after exhaustion of NADH, precedes that of cytochrome c. NADH oxidation is blocked by mersalyl, an inhibitor of NADH-cytochrome b5 reductase. These observations support the view of an electron transfer from the outer to the inner membrane of intact mitochondria. Both the rate of exogenous NADH oxidation and the steady state level of cytochrome c reduction increase with the increase of ionic strength, while the rate of succinate oxidation undergoes a parallel depression. These observations suggest that the functions of cytochrome c as an electron carrier in the inner membrane and as an electron shuttle in the intermembrane space are alternative. It is concluded that aerobic oxidation of exogenous NADH involves the following pathway: NADH leads to NADH-cytochrome b5 reductase leads to cytochrome b5 leads to intermembrane cytochrome c leads to cytochrome oxidase leads to oxygen. It is suggested that the communication between the outer and inner membranes mediated by cytochrome c may affect the oxidation-reduction level of cytosolic NADH and the related oxidation-reduction reactions.

Animals↗
PubMed1981

Effect of funiculosin and antimycin A on the redox-driven H+-pumps in mitochondria: on the nature of "leaks'.

The effect of antimycin A and funiculosin, two inhibitors which block electron transfer in the b-c1 complex, on electron flow and electrochemical potential difference of H+ ions in mitochondria at static head (state 4) is investigated. In addition, the respiratory control ratio is determined as the ratio between uncoupler stimulated and static-head electron flow. Malonate, a competitive inhibitor or succinic dehydrogenase, is used for comparison. All three inhibitors cause an extensive depression of static-head electron flow but only a limited decrease in the electrochemical potential difference of H+ ions. With the antimycin-type of inhibitors, the respiratory control ratio slightly increases up to about 50% inhibition of electron flow and then steeply declines. With malonate, a strong decrease of the respiratory control ratio is observed in a concentration range where the electron flow is inhibited less than 10%. It is shown than the data do not comply with the generally accepted hypothesis of a leak conductance being regulated by the electrochemical potential difference of H+ ions. They can be interpreted in terms of not tightly coupled redox-driven H+-pumps. A non-vanishing electron flow at static head then arises predominantly from molecular slipping in the pumps, and the (constant) leak conductance yields only a minor contribution.

Animals↗
PubMed1979

Kinetics of Ca2+ carrier in rat liver mitochondria.

The rate of aerobic Ca2+ transport is limited by the rate of the H+ pump rather than by the Ca2+ carrier. The kinetics of the Ca2+ carrier has therefore been studied by using the K+ diffusion potential as the driving force. The apparent Vmax of the Ca2+ carrier is, at 20 degrees C, about 900 nmol (mg of protein)-1 min-1, more than twice the rate of the H+ pump. The apparent Vmax is depressed by Mg2+ and Li+. This supports the view that the electrolytes act as noncompetitive inhibitors of the Ca2+ carrier. The degree of sigmoidicity of the kinetics of Ca2+ transport increases with the lowering of the temperature and proportionally with the concentration of impermeant electrolytes such as Mg2+ and Li+ but not choline. The effects of temperature and of electrolyte do not support the view that the sigmoidicity is due to modifications of the surface potential. Rather, they suggest that Ca2+ transport occurs through a multisubunit carrier, where cooperative phenomena are the result of ligand-induced conformational changes due to the interaction of several allosteric effectors with the carrier subunits. In contrast with La3+ which acts as a competitive inhibitor, Ruthenium Red affects the kinetics by inducing phenomena both of positive and of negative cooperativity. The Ruthenium Red induced kinetics has been reproduced through curve-fitting procedures by applying the Koshland sequential interaction hypothesis to a four-subunit Ca2+ carrier model.

Animals↗
PubMed1979

H+/site, charge/site, and ATP/site ratios in mitochondrial electron transport.

H(+)/site, charge/site, and ATP/site ratios have been determined at coupling sites I, II, and III. Three e(-) donors have been used for coupling site III: ferrocyanide, ascorbate + tetramethyl-p-phenylenediamine (TMPD), and succinate + TMPD. The H(+)/site ratios are 4.0 with ferrocyanide and 6.0 with succinate + TMPD (at pH <7.0); the charge/site ratios are 6.0 with ferrocyanide and with succinate + TMPD (at pH <7.0) and 4.0 with ascorbate + TMPD; the ATP/site ratio is 1.34 with ascorbate + ferrocyanide. These ratios have been obtained in the presence of amounts of antimycin A that provide full inhibition of site II. For coupling sites I and II, ferricyanide has been used as e(-) acceptor and succinate or NAD-linked substrates as e(-) donors. The H(+)/site ratios are 4.0 at sites I and II; the charge/site ratios are 4.0 at site I and 2.0 at site II; the ATP/site ratios are 1.0 at site I and 0.5 at site II. Two major factors affect the stoichiometries: (i) dimension of [unk](H) and (ii) supply of H(+) from the matrix. There is a correlation between collapse of [unk](H) and increase of H(+)/site and charge/site ratios. This indicates that approximation of the phenomenologic stoichiometry of the H(+) pump is obtained when flow ratios are measured at level flow. That charge/site and ATP/site ratios increase when ferrocyanide is e(-) donor and decrease when ferricyanide is e(-) acceptor is attributed to the localization of the redox couple. This leads to separation of 1 charge/e(-) when ferrocyanide is e(-) donor and to consumption of 1 charge/e(-) when ferricyanide is e(-) acceptor. To account for an extrusion of H(+) in excess of that predicted by the loop model, it is proposed that each coupling site contains a channel acting as a H(+) pump.

Adenosine Triphosphate↗
PubMed1978

Proton electrochemical gradient and rate of controlled respiration in mitochondria.

The correlation between deltamuH, the proton electrochemical potential difference, and the rate of controlled respiration is analyzed. deltamuH (the proton concentration gradient) is measured on the distribution of [3H]acetate, and deltapsi (the membrane potential) on the distribution of 86Rb+, 45Ca2+ and [3H]triphenylmethylphosphonium used either alone or simultaneously. The effects of the addition of ADP + hexokinase (state-3 ADP) and of carbonylcyanide trifluoromethoxyphenylhydrazone (state-3 uncoupler) on respiration and deltamuH are not equivalent: the uncoupler depresses deltamuH more than ADP at equivalent respiratory rates. The effects of the additions of nigericin-valinomycin and of ionophore A23187 (state-3 cation transport) and of carbonylcyanide trifluoromethoxy-phenylhydrazone (state 3-uncoupler) on respiration and deltamuH are also not equivalent: the uncoupler depresses deltamuH more than A23187 and nigericin + valinomycin at equivalent respiratory rate. A23187 is very efficient in stimulating respiration with negligible deltamuH changes.

Adenosine Diphosphate↗
PubMed1978

Proton electrochemical gradient and phosphate potential in mitochondria.

The paper reports an analysis of the relationship between deltamuH the proton electrochemical potential difference, and deltaGp, the phosphate potential. Depression of deltamuH and deltaGp has been obtained by titration with: (a) carbonylcyanide trifluoromethoxyphenylhydrazone; (b) nigericin (+ valinomycin); (c) KCl (+ valinomycin); and (d) rotenone. The uncoupler depresses deltamuH more than nigericin (+ valinomycin), KCl (+ valinomycin) and rotenone at equivalent deltaGp. The deltaGp/deltamuH ratio is about 3 at high values of deltamuH. When deltaGp and deltamuH are depressed by nigericin (4 valinomycin) the deltaGp/deltamuH ratio remains constant. When deltaGp and deltamuH are depressed by uncouplers, the deltaGp/deltamuH ratio increases hyperbolically tending to infinity while deltamuH tends to zero. The absence of constant proportionality between deltaGp and deltamuH indicates that the proton gradients driving ATP synthesis presumably operate within microscopic environments.

Adenosine Triphosphate↗
PubMed1978

Proton electrochemical gradient and phosphate potential in submitochondrial particles.

The aerobic uptake of inorganic ions, such as 86Rb+ or 125I-, by submitochondrial particles, is about one order of magnitude lower than the uptake of organic ions, such as acridines or 8-anilino-1-naphthalene sulphonate. The values of deltapH, the transmembrane pH differential, and deltapsi, the transmembrane membrane potential are between 60 and 100 mV when calculated on the inorganic ions and between 150 and 240 mV when calculated on the organic ions. The discrepancy between the deltapH and deltapsi values from organic and inorganic ions is large at high but not at low ion/protein ratios. 2. In the absence of weak bases and strong acids the values of deltamuH, the proton electrochemical potential difference, are close to 100 mV and the magnitude of deltapH and deltapsi are similar. Weak bases decrease deltapH and enhance deltapsi. Strong acids decrease deltapsi and enhance deltapH. Interchangeability of deltapH with deltapsi occurs at low concentrations of weak bases and strong acids. High concentrations of weak bases and strong acids cause depression of deltamuH. 3. Concentrations of weak bases capable of abolishing deltapH, do not affect ATP synthesis. Concentrations of strong acids capable of abolishing deltapsi affect only slightly ATP synthesis. Concentrations of weak bases and strong acids capable of causing a decline of deltapH + deltapsi inhibit ATP synthesis. 4. Depression of deltamuH is paralleled by inhibition of ATP synthesis and decline of deltaGp, the phosphate potential. Abolition of ATP synthesis occurs only when deltamuH is below 20 mV. The deltaGp/deltamuH ratio increases hyperbolically with the decrease of deltamuH.

Acridines↗