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Biomedical subjects

A Toninello

Publications and source records attributed to A Toninello.

At least 37 records · Page 2Linked to original sources
PubMed1996

Casein kinase 2 phosphorylates recombinant human spermidine/spermine N1-acetyltransferase on both serine and threonine residues.

Casein kinase 2 purified from human erythrocyte cytosol has been found to phosphorylate human spermidine/spermine N1-acetyltransferase (SSAT) expressed as a fusion protein in E. coli and purified to homogeneity with a specific activity similar to that reported for pure human SSAT. The amino acid sequence of the protein revealed not less than four phosphorylable residues, optimal target for protein kinase 2 phosphorylation being flanked by acid residues in position +1 and +3. Our results indicate that most 32P-phosphate is taken up by Ser residues, as evidenced by HCl hydrolysis and electrophoresis and that the phosphorylation extent is modulated by the physiological polyamine concentration. Partial digestion with trypsin at a low concentration for less than one hour preferentially hydrolyzes Lys-Arg-Arg in position 141-143 of the SSAT suggesting that the Ser-phosphorylated residues are located in the C-terminus of the protein, probably Ser 146 and 149.

Acetyltransferases↗
PubMed1996

Spermine binding to liver mitochondria.

Non-equilibrium binding of spermine to mitochondrial membranes is studied in rat liver mitochondria by applying a new thermodynamic treatment of ligand-receptor interactions (Di Noto, V., Dalla Via, L., Toninello, A. and Vidali, M. (1996) Macromol. Theory Simul. 5, 165-181). The presence on mitochondrial membranes of two spermine binding sites, both with monocoordination, is demonstrated. The calculated binding energy is characteristic for weak interactions. The treatment allows also to evaluate the variations of the molar fraction ratio of spermine bound to sites 1 and 2 as function of total bound spermine. The possible role of the two sites is discussed.

Animals↗
PubMed1996

The contribution of endogenous polyamines to the permeability transition of rat liver mitochondria.

Spermine and spermidine are present in rat liver mitochondria at the concentrations of 3.5 and 1.8 nanomoles/mg protein, respectively. Addition of 50 microM Ca2+ and 1 mM Pi to respiring mitochondria induces, concomitantly with mitochondrial swelling and Mg2+ efflux, a consistent release of polyamines, which is either prevented by cyclosporin A or Mg2+. Addition of 0.1 mM spermine to mitochondria deenergized by Ca2+ and phosphate restores, like 1 mM Mg2+, transmembrane potential at the physiological level, while either cyclosporin A or ADP are ineffective. The presence of polyamines in the matrix space should be considered relevant, like Mg2+, in controlling the permeability transition of liver mitochondria.

Animals↗
PubMed1995

The alterations in the energy linked properties induced in rat liver mitochondria by acetylsalicylate are prevented by cyclosporin A or Mg2+.

The alterations in rat liver mitochondria induced by acetylsalicylate in the presence of low concentrations of Ca2+ (large amplitude swelling, permeability to 14C]sucrose, collapse of transmembrane potential and effluxes of endogenous Mg2+ and accumulated Ca2+) were fully prevented by either cyclosporin A or Mg2+. Cyclosporin A and Mg2+ were also capable of restoring transmembrane potential upon its decrease induced by acetylsalicylate. The loss of endogenous Mg2+ was the primary effect promoted by acetylsalicylate; the other noxious effects followed. These results indicate that Mg2+ are fundamental components of the mitochondrial permeability barrier and that their loss might be responsible for the membrane transition induced by acetylsalicylate.

Animals↗
PubMed1995

Inhibition of mitochondrial permeability transition by polyamines and magnesium: importance of the number and distribution of electric charges.

The protective effects of Mg2+ and various natural and synthetic polyamines on the permeability transition of isolated rat liver mitochondria have been compared. The permeability transition was induced by incubating the mitochondria in a sucrose medium at pH 7.4 in the presence of 100 microM Ca2+ and 1 mM phosphate and was monitored via the release of endogenous Mg2+, sucrose permeation, mitochondria swelling and the fall of transmembrane potential. By all of these parameters (only the traces of delta psi have been reported) spermine fully inhibited the transition at 25 microM concentration, spermidine and caldine at 250 microM and Mg2+ at 500 microM concentration. Both putrescine and dien exhibited only a partial protection even at 2.5 mM concentration. The protective action resulted strictly dependent on the number of the positive charges of each cation. In the case of polyamines this number is also determined by the nature of the methylene carbon chains of each compound.

Animals↗
PubMed1994

Spermine effect on the binding of casein kinase I to the rat liver mitochondrial structures.

The results indicated here, together with those previously reported, show that spermine, ubiquitous polyamine, while promoting the transmembrane translocation of casein kinase II (CKII) across the outer membrane to more internal compartments of rat liver mitochondria, promotes the binding of casein kinase I (CKI) to the external surface of outer mitochondrial membrane but inhibits its spontaneously occurring binding to more internal structures.

Animals↗
PubMed1994

Spermine-mediated casein kinase II-uptake by rat liver mitochondria.

Spermine, ubiquitous intracellular polyamine, is able to promote the transmembrane translocation of casein kinase CKII through the outer membrane of rat liver mitochondria and its binding to more internal mitochondrial structures. These findings suggest that spermine may play a critical role in regulating the subcellular distribution of casein kinase CKII.

Animals↗
PubMed1993

Effect of spermine on mitochondrial glutathione release.

Spermine prevents glutathione release induced in rat liver mitochondria by the combined addition of Ca2+ and phosphate. Spermine also inhibits mitochondrial swelling, membrane potential decrease, oxygen uptake and [14C] sucrose entry stimulated by the above reported agent. Mitochondrial swelling is completely prevented by 25 microM spermine while higher concentrations (100 microM) are required for the full inhibition of glutathione release. Therefore, polyamines decrease the mitochondrial inner membrane permeability and, by preventing mitochondrial glutathione loss, also act as protective agents against oxidative stress.

Animals↗
PubMed1992

Effects of palmitoyl CoA and palmitoyl carnitine on the membrane potential and Mg2+ content of rat heart mitochondria.

Palmitoyl CoA and palmitoyl carnitine added to rat heart mitochondria in amounts above 20 and 50 nmoles/mg protein, respectively, induced a fall in transmembrane potential and loss of endogenous Mg2+. The dissipation of membrane potential by low concentrations of palmitoyl CoA in the presence of Ca2+, but not that of high concentrations of palmitoyl CoA alone, was prevented by either ruthenium red, Cyclosporin A or Mg2+, but reversed only by Mg2+. The fall of membrane potential induced by palmitoyl carnitine was not prevented by any of these factors. It is suggested that the action of both palmitoyl CoA and palmitoyl carnitine at high concentrations is due to a non specific disruption of membrane architecture, while that of low concentrations of palmitoyl CoA in the presence of Ca2+ is associated specifically with energy dissipation due to Ca2+ cycling.

Animals↗
PubMed1992

Evidence that spermine, spermidine, and putrescine are transported electrophoretically in mitochondria by a specific polyamine uniporter.

We present evidence that polyamine uptake into rat liver mitochondria is mediated by a specific polyamine uniporter. Polyamine transport is not mediated by the ornithine, lysine, or Ca2+ transporters of mitochondria. Polyamine transport is a saturable process, with apparent Km values of 0.13 mM for spermine, 0.26 mM for spermidine, and 1 mM for putrescine. These substrates are mutually competitive inhibitors, indicating a common transport system. Polyamine transport is strictly dependent on membrane potential and insensitive to medium pH, showing that these polycations are transported electrophoretically. Spermine, spermidine, and putrescine are taken up by rat liver mitochondria at rates that increase with increasing valence of the transported species. The activation enthalpies for transport were 24, 32, and 59 kJ/mol for putrescine, spermidine, and spermine, respectively. These values, which amount to about 12 kJ/mol per charge transferred, may be compared to a value of 76 kJ/mol observed for monovalent tetraethylammonium cation. Flux-voltage analysis is consistent with the hypothesis that the mitochondrial polyamine transporter catalyzes transport via a channel mechanism.

Animals↗
PubMed1992

Bidirectional transport of spermine in rat liver mitochondria.

Further study of the mitochondrial transport of spermine (Toninello et al. (1988) J. Biol. Chem. 263, 19407) shows that, after loading rat liver mitochondria with [14C]spermine and [32P]phosphate, these components are released together into the surrounding medium by adding mersalyl or N-ethylmaleimide. On later addition of dithioerythritol, both are recaptured, but if acetate or nigericin are added instead, only spermine re-enters and there is continued export of phosphate. This bidirectional transport of spermine in and out mitochondria is driven, respectively, by membrane potential and pH gradient at constant protonmotive force. Results using [14C]spermine or [32P]phosphate, in conjunction with the their unlabelled isomers and with or without carbonyl cyanide/p-trifuloromethoxyphenylhydrazone (FCCP) present suggest that there is a continuous energy-dependent efflux-influx cycling of spermine and phosphate.

Animals↗
PubMed1990

Transport and action of spermine in rat heart mitochondria.

At concentrations of 0.5-1.0 mM, spermine fully prevents the fall of membrane potential induced in rat heart mitochondria either by aging at room temperature or by the addition of palmitoyl CoA. Spermine also prevents the inhibitory action of palmitoyl CoA on adenylate translocase activity. When added to heart mitochondria de-energized by the same damaging conditions (aging or addition of palmitoyl CoA) spermine restores both membrane potential (provided that ATP is also added) and the activity of adenylate translocase. A part of added spermine is immediately bound to anionic sites on mitochondrial membranes, another part is slowly transported into heart mitochondria. Whereas binding is an energy independent process, transport is driven by the transmembrane potential. Spermine penetrates the mitochondrial matrix at significant rates only at high membrane potential, such as that produced either by phosphate transport or addition of nigericin.

Adenosine Triphosphate↗
PubMed1988

On the mechanism of spermine transport in liver mitochondria.

Spermine penetrates the mitochondrial matrix at significant rates which increase sharply and non-ohmically with membrane potential. In this respect, spermine uptake is qualitatively similar to that of other cations whose electrophoretic transport has been studied in mitochondria. At 200 mV and 1 mM spermine, the observed rate of spermine uptake was about 7 nmol x mg-1 x min-1, and the rate constant was about 8 times greater than that of tetraethylammonium cation. These rates are remarkably rapid considering that spermine is largely tetravalent at the pH of the experiment. The fluxes of spermine and tetraethylammonium are log-linear with membrane potential. The slope of the tetraethylammonium plot is consistent with leakage of this ion across a sharp Eyring barrier located in the middle of the membrane. The slope of the spermine plot is half that predicted by such a leak pathway, raising the possibility that spermine may cross the inner membrane by means of a channel. Whatever its mechanism of penetration, if comparable rates of uptake obtain in vivo and if spermine is not metabolized within the mitochondrial matrix, then a separate efflux mechanism would appear to be required to prevent unlimited spermine loading.

Animals↗
PubMed1988

Protective action of methylglyoxal bis (guanylhydrazone) on the mitochondrial membrane.

At low concentrations (0.5-1.0 mM) methylglyoxal bis (guanylhydrazone) (MGBG) exhibited a clearcut protection of rat liver mitochondria against the deenergizing action of either Ca2+, or oxidizing agents (butylhydroperoxide and oxaloacetate). Such a protection resulted from the prevention of transmembrane potential decay, discharge of accumulated Ca2+, release of mitochondrial Mg2+, adenine nucleotides and pyridine nucleotides and mitochondrial swelling. At high concentrations (5-10 mM) MGBG induced functional alterations of mitochondria (decrease of transmembrane potential, lower capability to accumulate and to retain Ca2+) which can be reversed by resuspension of mitochondria in a MGBG free medium. These reversible mitochondrial alterations by high MGBG concentrations are interpreted as a consequence of an aggregation and coprecipitation of suspended mitochondria.

Adenosine Triphosphate↗
PubMed1986

L-carnitine effect on halothane-treated mitochondria.

Addition of halothane to the incubation medium is shown to lower respiratory control and transmembrane potential and to increase ATPase activity in isolated rat liver mitochondria. Evidence is presented that L-carnitine is able to substantially decrease the negative effects of halothane on the energy-linked processes of mitochondria. The effects of halothane and the protective action of L-carnitine are discussed in the light of a possible involvement of long-chain acyl CoA in the unpairing of mitochondrial energy-linked functions.

Acyl Coenzyme A↗
PubMed1986

Involvement of long-chain acyl CoA in the antagonistic effects of halothane and L-carnitine on mitochondrial energy-linked processes.

Incubation of rat liver mitochondria in the presence of halothane induced a consistent impairment of mitochondrial oxidative phosphorylation without significantly affecting the steady-state of transmembrane electrical potential. These alterations of mitochondrial energy-linked processes were associated with a consistent accumulation of long-chain acyl CoA. Addition of L-carnitine partially prevented the effects of halothane on oxidative phosphorylation and completely abolished the halothane-induced long-chain acyl CoA accumulation. The possibility is discussed that the damaging action of halothane on mitochondrial functions might be partially ascribed to the noxious action of the excess of long-chain acyl CoA induced the anesthetic.

Acyl Coenzyme A↗