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V Petronilli

Publications and source records attributed to V Petronilli.

46 records · Page 3Linked to original sources
PubMed1989

The inner mitochondrial membrane contains ion-conducting channels similar to those found in bacteria.

Patch-clamp experiments were performed on rat liver mitochondria inner membranes. Application of voltage gradients of either polarity revealed the presence of several different conductances, ranging up to 1.3 nS in symmetrical 150 mM KCl. Evidence is presented that at least those higher than 0.3 nS are substates of the highest conductance channel. Increasing matrix-side-positive (unphysiological) transmembrane voltage gradients favored the switch of the 1.3 nS channel to operation in lower conductance states. The size of these conductances, the presence of substates and the channel behavior are strongly reminiscent on one hand of the observations on the membrane of protoplasts from the gram-positive bacterium Streptococcus faecalis, [Zoratti, M. and Petronilli, V. (1988) FEBS Lett. 240, 105-109], and on the other of some properties of previously described channels of mitochondrial origin.

Animals↗
PubMed1988

Ion-conducting channels in a gram-positive bacterium.

The patch-clamp technique was used to obtain information on the existence and properties of ion channels in giant protoplasts obtained from the Gram-positive bacterium Streptococcus faecalis. The membrane proved to contain a pore with numerous conductance states, ranging from 10 pS to several nanosiemens. Application of a slight pressure differential across the membrane resulted in the activation of the channel. The pressure sensitivity points to a relationship between this channel and one recently discovered in E. coli spheroplasts [(1987) Proc. Natl. Acad. Sci. USA 84, 2297-2301] suggesting that pores of this type might be widespread among prokaryotes.

Electric Conductivity↗
PubMed1988

Analysis of mechanisms of free-energy coupling and uncoupling by inhibitor titrations: theory, computer modeling and experiments.

The rates of ATP synthesis and of ATP-driven NAD reduction have been measured in bovine heart submitochondrial particles as a function of the fraction of inhibited redox pumps (in titrations with either antimycin or rotenone) and of the fraction of inhibited ATPases (in titrations with DCCD). The flux control coefficients of the redox and ATPase proton pumps on the rates of ATP synthesis and of ATP-driven NAD reduction have been derived and found to be equal to 1 for both pumps; i.e., both pumps appear to be 'completely rate limiting'. A theoretical analysis of the inhibitor titration approach based on kinetic models of chemiosmotic coupling and on the theory of metabolic control is presented. This analysis (i) shows that the results of the single inhibitor titrations are incompatible with a delocalized chemiosmotic mechanism of energy coupling if the proton conductance of the membrane is sufficiently low with respect to the conductances of the pumps; and (ii) suggests an experimental approach based on the determination of the P/O and the respiratory control ratios at different degrees of inhibition of the proton pumps to establish the origin of the 'loose coupling' of submitochondrial particle preparations. Three independent types of observation show that the 'loose coupling' of the particle preparation is not mainly due to an increased membrane proton conductance. The same and other independent observations are consistent with the view that the loose coupling of submitochondrial particle preparation is due mainly to inhomogeneity, i.e. to the presence of a subpopulation of highly leaky non-phosphorylating vesicles respiring at maximal rate. The results as a whole together with the simulations and analysis presented lead to the conclusion that the mechanism of free-energy coupling in submitochondrial particles is not completely delocalized.

Adenosine Triphosphatases↗
PubMed1986

ATP synthase-mediated proton fluxes and phosphorylation in rat liver mitochondria: dependence on delta mu H.

The dependence of the proton flux through the ATP synthases of rat liver mitochondria on a driving force composed mainly of a potassium diffusion potential was determined and compared with the relationship between rate of phosphorylation and delta mu H given by titrations with the respiratory inhibitor malonate. The two functions are in good agreement in the lower part of the delta mu H range covered. However, the maximal proton fluxes through the ATP synthases are much lower than needed to account for the rate of State 3 phosphorylation sustained by the same mitochondria oxidizing succinate. Possible reasons for this behavior are discussed.

Animals↗
PubMed1986

Free energy coupling between H+-generating and H+-consuming pumps. Ratio between output and input forces.

The delta Gp/delta mu H ratio has been measured in mitochondria close to state 4 in the presence of various uncoupler or K+/valinomycin concentrations in media containing either 1 mM or 50 mM Pi. Care has been taken to control the factors affecting delta Gp and delta mu H which could lead to an artefactual increase of the delta Gp/delta mu H ratio above the highest accepted value for the H+/ATP stoichiometry (n = 4, synthesis + transport). In particular, to avoid overestimation of delta Gp due to inactivation of the ATPases at low delta mu H or to the presence of adenylate kinase, the static head state was approached from the side of net ATP synthesis and delta Gp was measured in a state close to static head but still maintaining a residual rate of aerobic phosphorylation. For each concentration of uncoupler or K+, the Pi concentration and/or the adenylate energy charge (EC) as a function of time have been measured as indicators of net ATP synthesis. Only the values of delta Gp measured during a decrease in Pi concentration and/or an increase in EC have been considered to be meaningful for calculations of delta Gp/delta mu H ratios. Both uncouplers and K+ transport cause a marked depression of delta mu H and a parallel depression of the rate of ATP synthesis. However the low rate of ATP synthesis taking place under conditions of low delta mu H eventually results, especially at high Pi concentrations, in a relatively large delta Gp. The delta Gp/delta mu H ratios obtained at the lower delta mu H values exceed 4 and approach 6. Although slightly higher delta Gp/delta mu H ratios are obtained with valinomycin-treated than with uncoupler-treated mitochondria, the pattern of the rise of the force ratio as delta mu H decreases is similar in both cases. An increase of the delta Gp/delta mu H ratio above 4, the maximal accepted H+/ATP stoichiometry is thermodynamically incompatible with the delocalized protonic coupling model.

Adenosine Triphosphate↗
PubMed1985

Multiple relationships between rate of oxidative phosphorylation and delta microH in rat liver mitochondria.

The relationship between rate of ATP synthesis and transmembrane electrochemical proton gradient has been determined in rat liver mitochondria oxidizing succinate, using the respiratory inhibitor malonate or the uncoupler FCCP to decrease delta microH progressively. As previously reported [(1982) Eur. J. Biochem. 126, 443-451] two different relationships are obtained depending on the method used. Evidence is presented that this result is not due to underestimation of the delta microH maintained by fast-respiring mitochondria, as recently suggested [(1985) FEBS Lett. 181, 323-327].

Adenosine Triphosphate↗
PubMed1984

Nigericin-induced transient changes in rat-liver mitochondria.

Addition of nigericin to mitochondria oxidizing succinate in a choline- and Tris-supplemented, low-KCl medium leads to a transient matrix acidification, followed by a return of pHin to values very close to pHout. The initial inhibition of stimulated respiration is gradually relieved as pHin returns to higher values. Matrix realkalinization depends on the operation of the H+ pumps and on the electrogenic influx of cations and efflux of anions. The process leads to replacement of much of the matrix K+ by other cations. Throughout the acidification/realkalinization cycle delta mu H variations, if any, are small, even though there are profound changes in the relative contributions of its two components, delta psi and delta pH.

Animals↗
PubMedDate not supplied

The stoichiometry of H+ pumping in cytochrome oxidase and the mechanism of uncoupling.

It is suggested that loose coupling in free energy transducing organelles is due partly to leaks through the phospholipid bilayer (extrinsic uncoupling) and partly to "slipping" of the proton pumps (intrinsic uncoupling). The flow ratio of the redox pumps (JH/JO) measured at level flow is not affected by extrinsic uncoupling, but it will be lower the higher the extent of intrinsic uncoupling. During operation of cytochrome oxidase with ferrocyanide or N,N,N',N'-tetraphenyl-p-phenylenediamine as substrates, the rate of resting respiration depends on substrate concentration and does not exhibit control by delta muH; the available data strongly suggest that the enzyme is intrinsically uncoupled to a high and variable (substrate concentration-dependent) extent. It is concluded that flow ratios (at level flows) provide underestimates of the cytochrome oxidase pump stoichiometry.

Biological Transport↗