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Biomedical subjects

E Carafoli

Publications and source records attributed to E Carafoli.

At least 253 records · Page 14Linked to original sources
PubMed1981

Hyperbolic kinetics of the electrophoretic carrier of Ca2+ uptake in liver mitochondria.

The use of a fast-responding Ca2+-selective electrode has allowed the simultaneous measurement of the true Ca2+-activity in the medium and of the Ca2+-transport rate, eliminating the uncertainties connected with the use of indirect methods of estimating Ca2+ transport rates (e.g. O2-stimulation, K+-efflux). The results on the kinetics of Ca2+ uptake by rat liver mitochondria obtained in this study are qualitatively similar to those obtained by Bragadin et al. [Bragadin, M., Pozzan, T. & Azzone, G. F. (1979) Biochemistry, 18, 5973--5978] by monitoring the K+-efflux from mitochondria. In the valinomycin-driven Ca2+ uptake, the Ca2+ translocase is the limiting factor, whereas in the system driven by succinate extraneous limiting factors play a role. Thus, liver mitochondria, when studied under appropriate non-limiting conditions, exhibit a hyperbolic dependence on the Ca2+ uptake rate on Ca2+-activity analogous to that of mitochondria from other tissues. The sigmoidal dependence of the uptake rate on Ca2+-activity in liver mitochondria, observed under conditions which produce hyperbolic kinetics in mitochondria from other tissues, can thus be attributed to factors which are extraneous to the Ca2+ transport system per se.

Animals↗
PubMed1981

The fatty acid composition of subcellular membranes of rat liver, heart, and brain: diet-induced modifications.

The influence of diets having different fatty acids composition on the fatty acid content of (the phospholipids) of rat liver mitochondria and microsomes, heart mitochondria, brain mitochondria and microsomes has been analyzed. It has been found that each organelle has its own peculiar composition in fatty acids. This composition may be profoundly influenced by the diet, but to different degrees in different organelles. Those of brain are most resistant. The changes observed are rather rapid, being generally already maximal after three weeks of treatment. The parallel between fatty acid composition of diets, and the changes observed in the organelles, is not strict, and is probably influenced by the metabolic competition among oleic acid, linoleic acid, linolenic acid. Unusual fatty acids like erucic acid, trans-oleic acid, and trans-linoleic acid can also become incorporated into the membranes of cell organelles.

Animals↗
PubMed1981

Interaction of the purified Ca2+, Mg2+-ATPase from human erythrocytes with phospholipids and calmodulin.

The Ca2+-pumping ATPase has been purified in a functional form from human erythrocytes by calmodulin affinity chromatography. The purified enzyme has a specific activity at least 300-fold higher than the membrane bound enzyme. It consists of one major protein band of 140000 Dalton, and after reconstitution in liposomes it transports Ca2+ with an efficiency of at least 1 Ca2+/ATP. In the presence of calmodulin, the affinity of the enzyme for Ca2+, and its specific activity, are greatly increased. Acidic phospholipids have an unexpected effect on the isolated enzyme: ATPase isolated or reconstituted in acidic phospholipids behaves as if calmodulin were present. Acidic phospholipids mimic the effect of calmodulin.

Ca(2+) Mg(2+)-ATPase↗
PubMed1980

Hydroperoxide-induced loss of pyridine nucleotides and release of calcium from rat liver mitochondria.

It has been previously reported (Lötscher, H. R., Winterhalter, K. H., Carafoli, E., and Richter, C. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 4340-4344) that in Ca2+-loaded mitochondria hydroperoxides induce a release of Ca2+ from mitochondria and an irreversible oxidation of mitochondrial pyridine nucleotides. Here we show that in the presence of Ca2+ oxidized mitochondrial pyridine nucleotides are hydrolyzed inside mitochondria and that nicotinamide is released from mitochondria. The extent of the hydrolysis of NAD(P)+ is dependent on the amount of both hydroperoxide and Ca2+. The hydrolysis is reversible in the presence of added nicotinamide. The release of Ca2+ from mitochondria is electroneutral, and is directly or indirectly dependent on oxidized mitochondrial pyridine nucleotides. By contrast, the uptake of Ca2+ most probably does not require the present of reduced pyridine nucleotides. Control experiments show that even under the most drastic conditions employed in this study (100 nmol of Ca2+ and 85 nmol of t-butylhydroperoxide/mg of protein) mitochondria retain a considerable degree of functional integrity.

Animals↗
PubMed1980

Cytochrome oxidase rotates in the inner membrane of intact mitochondria and submitochondrial particles.

A transient dichroism is detected after photolysis by a linearly polarized laser flash of the cytochrome oxidaseCO complex in bovine heart mitochondria, rat heart mitochondria, and bovine heart submitochondrial particles. A decay in the absorption anisotropy is characterized by a time constant of about 300 to 400 mus in both mitochondria and submitochondrial particles. Since vesicle tumbling in the time range less than 5 ms can be excluded in these experiments, we conclude that cytochrome oxidase rotates in the mitochondrial membrane with a relaxation time of several hundred microseconds. However, it is likely that only about one-half of cytochrome oxidase contributes to the observed decay, the remainder being relatively immobile.

Animals↗
PubMed1980

Charge movements during the Na+-Ca2+ exchange in heart sarcolemmal vesicles.

The Na+-Ca2+ exchange was studied in a highly purified vesicular preparation derived from heart sarcolemma. The initial velocity of the Na+-driven Ca2+ influx, which was monitored continuously with a specific electrode, was 15 nmol/mg of protein per sec; the total Ca2+-accumulation capacity was 80 nmol/mg of protein. The Na+-Ca2+ exchange generated a current that was compensated for by the uptake of tetraphenylphosphonium in (Ph4P+) (when the latter was present in the medium), the influx of K+, and the efflux of Cl-. The movements of Ph4P were followed with a specific electrode. Ca2+ in the concentration range 3-50 microM induced an increase in the permeability of the sarcolemmal membrane to K+. Under conditions of optimal charge neutralization by K+ (i.e., in the presence of valinomycin), the Km (Ca2+) of the exchanger was 1.5 microM. The Na+-Ca2+ exchange was inhibited by chlorpromazine and was not inhibited by vanadate.

Animals↗
PubMed1980

The energy-state of mitochondria during the transport of Ca2+.

The fluctuations of the membrane potential during mitochondrial Ca2+ transport have been monitored with an electrode sensitive to tetraphenylphosphonium. The following conclusions have been reached. 1. The membrane becomes depolarized during the influx of Ca2+. When the bulk of the Ca2+ pulse has been taken up, it repolarizes, but not completely. 2. If all of the accumulated Ca2+ is released from mitochondria and cycling is inhibited, the membrane repolarizes completely. 3. The accumulation of Ca2+ alone does not induce mitochondrial damage. In the presence of inorganic phosphate, the uptake of Ca2+ may lead to complete and irreversible depolarization, depending on the amount of Ca2+ and phosphate accumulated. The irreversible damage observed in the presence of phosphate is prevented by Mg2+.

Animals↗
PubMed1980

The role of inorganic phosphate in the release of Ca2+ from rat-liver mitochondria.

The effect of inorganic phosphate on Ca2+ retention has been investigated using phosphate-depleted liver mitchondria. Phosphate induces the release of Ca2+ through an efflux route insensitive to ruthenium red. This effect is not due to functional or structural damage, since mitochondria maintain their membrane potential during phosphate-induced Ca2+ efflux. Direct enzymatic measurement of mitochondria pyridine nucleotides has established that changes in their redox state (i.e. increased oxidation) do not play a role in the phosphate-effect. The phosphate-induced Ca2+ efflux requires transport of phosphate out of mitochondria. However, the fluxes of Ca2+ and phosphate do not coincide: the release of phosphate preceeds that of Ca2+.

Animals↗
PubMed1980

Quantitative analysis of the proton and charge stoichiometry of cytochrome c oxidase from beef heart reconstituted into phospholipid vesicles.

The proton and charge stoichiometry of cytochrome c oxidase reconstituted into phospholipid vesicles has been analysed using a fast responding oxygen electrode and a system for the simultaneous measurement of H+, K+ or lipophilic cations, and O2. From initial rate measurements after addition of reductant (ascorbate /N,N,N',N'-tetramethyl-p-phenylenediamine) the following stoichiometries could be extrapolated: K+/e-, between 1.85 and 2.05, H+/e-, between 0.58 and 0.75. Lipophilic cations can replace valinomycin/potassium as the charge . compensating system. Net H+ extrusion was observed for up to 11 turnovers of the enzyme (11 O2/cytochrome aa3). The variation of the internal pH buffering capacity of the vesicles has an influence on the number of turnovers during which net proton translocation can be observed, but has no influence on the determined stoichiometries.

Animals↗
PubMed1980

Ca2+, K+ redistributions and alpha-adrenergic activation of glycogenolysis in perfused rat livers.

1. The alpha-adrenergic activation of glycogenolysis was investigated in isolated rat livers perfused in a non-recirculating system. Net uptake and/or release of Ca2+, K+ and H+ by the liver (measured by ion-selective electrodes) were correlated with the glycogenolytic effects of phenylephrine. Uptake and retention of 45Ca by the mitochondria of perfused livers were studied to obtain information on the role played by exchangeable mitochondrial calcium in alpha-adrenergic activation of glycogenolysis. 2. Between 1 and 5 min after starting the addition of phenylephrine a net release of Ca2+ was observed, this was paralleled by an uptake of K+. Production rates of glucose and lactate from endogenous glycogen started to increase at the same time. During the following minutes K+ was released. 2 mM EGTA and a high concentration of Mg2+ strongly diminished the ionic and metabolic responses to phenylephrine, 0.2 mM EGTA was less effective. 3. High concentrations of K+ prevented the metabolic response to phenylephrine but had no effect on the release of Ca2+ into the extracellular medium. Tetracaine activated glycogenolysis and suppressed all the effects of the alpha-adrenergic agonist. 4. Experiments with 45Ca provided no evidence for an alpha-adrenergic release of Ca2+ from the exchangeable mitochondrial pool. Incorporation of 45Ca into the mitochondria of perfused livers was enhanced by phenylephrine. 5. We propose that the alpha-adrenergic release of Ca2+ from a pool located close to the surface of the cell is capable of triggering the glycogenolytic response.

Adrenergic alpha-Agonists↗