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Biomedical subjects

S Massari

Publications and source records attributed to S Massari.

At least 55 records · Page 3Linked to original sources
PubMed1977

The generation of the proton electrochemical potential and its role in energy transduction.

The evidence that all energy transducing membranes can generate a proton electrochemical potential difference, delta micronH, across the membrane and that this potential can be used to transfer energy among energy transducing units and to generate ATP, has increased the interest for the view that delta micronH plays an obligatory role in energy transduction and ATP synthesis. In the present article we shall concentrate on two experimental questions related with the generation and role of delta micronH: (a) the charge/site ratio; (b) the relation between the proton electrochemical potential on one side and the cation electrochemical potential, the phosphate potential and the redox potential on the other. We shall then discuss the view that energy transduction corresponds to a molecular energy machine rather than to a fuel cell.

Adenosine Triphosphate↗
PubMed1977

Phosphatidic acid distribution on the external surface of mixed vesicles.

A new method has been developed to detect the distribution of phosphatidic acid on the external surface of mixed phospholipid vesicles. Some positive dyes undergo large absorbance changes when the spatial separation between two or more dye molecules is smaller than a critical distance. When these dyes interact with mixed phospholipid vesicles, the absorbance changes may be utilized to calculate the amount of phosphatidic acid molecules which, on the external surface, occupy nearby positions not exceeding the critical dye distance, i.e., the amount of paired phosphatidic acid molecules. This amount was found to be higher than that calculated by statistical methods, indicating that phosphatidic acid molecules tend to be associated, in spite of the electrostatic repulsion between negative groups. The dependence of the amount of paired phosphatidic acid molecules on the pH, phosphatidylcholine:phosphatidic acid ratio, and temperature has been also analyzed.

Acridines↗
PubMed1977

Cation transport in cytochrome oxidase reconstituted vesicles.

Cation translocation across the membrane of cytochrome oxidase reconstituted vesicles may be followed with a simple spectrophotometric method. Cytochrome oxidase reconstituted vesicles, supplemented with ascorbate and cytochrome c. induce large spectral changes of the positive dye safranine, reversed by uncouplers and inhibitors of respiration. The dye is probably accumulated in the inner space of the vesicles, where it reaches high concentrations and aggregates. The spectral shifts and the absorbance changes, due to aggregation, are proportional to the amount of the dye taken up and depend on the respiratory control. In the presence of potassium, valinomycin causes an inhibition, whereas nigericin stimulates the dye uptake. The data are discussed in terms of electrical potential dependent fluxes.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1976

Anion and amine uptake and uncoupling in submitochondrial particles.

1. Unlike chloroplasts, submitochondrial particles are not uncoupled by nigericin + KCl or NH4Cl. Also the uncoupling effect of lipophilic anions is largely independent of the addition of weak bases. 2. Low concentrations of permeant anions cause a shift of the steady-state energy level rather than a cycle of energy utilization. The degree of inhibition of ATP synthesis by tetraphenylboron is larger than required for the uptake of the anion. 3. Lipophilic anions such as bromthymolblue, bromcresolpurple, and 8-anilino-1-napthalene sulphonate cause a pH-independent, 50% uncoupling in submitochondrial particles at concentrations of 3, 30 and 30 muM, respectively. The passive interaction of bromthymolblue and bromcresolpurple appears as a pH-dependent distribution between two pHases. ATP causes a pH-independent slight shift in the anion distribution, with negligible anion accumulation. 4. Addition of amines to energized submitochondrial particles results in two types of effects; uptake of amines and uncoupling. While in chloroplasts amine uptake and uncoupling are closely associated, this is not the case in submitochondrial particles. The uncoupling effect is observed only with lipophilic and not with hydrophilic amines, and the degree of uncoupling increases with the lipophilicity of the amines. The amine uptake, on the other hand, is accompanied by negligible uncoupling. 5. While the uptake of amines is dependent on the presence of non-permeant anions, such as Cl-, the uncoupling effect is independent of Cl-. Furthermore the amine uncoupling is markedly enhanced by lipophilic anions. 6. The view is discussed that the uncoupling effect of lipophilic anions and lipophilic amines in submitochondrial particles is due to a catalytic energy dissipation rather than to a stoichiometry energy utilization. The molecular mechanism of uncoupling presumably involves a cycling of charges after a perturbation of the membrane structure.

Amines↗
PubMed1976

Mechanism of active shrinkage in mitochondria. I. Coupling between weak electrolyte fluxes.

1. A passive penetration of (NH4)2 HPO4 or of K2HPO4+nigericin occurs in respiratory-inhibited liver mitochondria. Addition of succinate at the end of the passive swelling initiates a shrinkage phase which leads to restoration of the initial mitochondrial volume. The rate and time of onset of the active shrinkage depend on the degree of stretching of the mitochondrial membrane. The rate of active shrinkage increases proportionally to the concentration of nigericin while it is strongly inhibited by valinomycin. 2. A number of SH inhibitors such as N-ethylmaleimide, p-chloromercuribenzoate, p-chloromercuriphenylsulphonate, dithiobisnitrobenzoate, exert a marked enhancing effect on the rate of shrinkage. The enhancing effect parallels titration of the phosphate carrier and inhibition of the passive phosphate efflux. In contrast, mersalyl is a powerful inhibitor of the rate of active shrinkage. The inhibition parallels that on phosphate passive efflux and requires higher mersalyl concentrations in respect to inhibition of phosphate influx. 3. The active shrinkage is discussed in terms of (a) a mechanoenzyme, (b) an electrogenic proton pump and (c) a proton-driven Pi pump.

Animals↗
PubMed1976

The interaction of organic cations with the mitochondrial membrane.

Weak and strong organic bases behave in an opposite manner in respect to several mitochondrial functions. The former induce a catalytic exchange with K+ in valinomycon-treated, respiratory-inhibited mitochondria, and act as uncouplers in respiring mitochondria. The latter induce a stoicheometric exchange with K+ and are actively taken up by respiring mitochondria.

Adenosine Triphosphatases↗
PubMed1975

The interaction of atebrin with phospholipid vesicles.

The interaction of atebrin with phosphatidylcholine and phosphatidylcholine-phosphatidic acid vesicles has been followed by equilibrium dialysis, and by photometric, fluorimetric and NMR techniques. The presence of negative charges in the phospholipids enhances the binding of atebrin. The absorbance and NMR spectral changes and fluorescence quenching occurring with phosphatidic acid are attributed to dimerization of the dye interacting electrostatically with negative groups. The dissociation constant of the binding of the dye to phosphatidylcholine vesicles was 1.4 mM; those of binding to the negative sites of phosphatidic acid were approx. 150 and 3 muM. The dye is probably located at the interphase with the acridine ring interacting with the anionic groups of phosphatidic acid and the tail freely floating in the aqueous phase. The results are discussed also in view of the use of atebrin as a probe of the energized state in natural membranes and of the suggestion that atebrin may be used as a transmembrane pH indicator in liposomes or natural membranes.

Binding Sites↗