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G Sandri

Publications and source records attributed to G Sandri.

At least 37 records · Page 2Linked to original sources
PubMed1988

Influence of Ca2+ on the isolation from rat brain mitochondria of a fraction enriched of boundary membrane contact sites.

Data have been obtained suggesting that the complex porin-hexokinase of brain mitochondria may be related to the contact sites between the outer and inner membrane. In the attempt to isolate from brain mitochondria the inner and outer membranes and the boundary membrane contacts, a procedure was developed based on swelling and shrinking of the organelles, followed by sonication and reverse discontinuous density gradient centrifugation. Three fractions were obtained by this technique, which were identified by measuring the relative specific activities of marker enzymes, namely succinate-cytochrome c reductase; NADH-cytochrome c reductase (rotenone insensitive); hexokinase and glutathione transferase, for the inner and outer membranes and contact sites, respectively. The fraction which contains the contact sites is characterized by the highest specific activity of hexokinase and glutathione transferase and by the highest calcium binding capacity; physiological concentrations of this cation produces a sharper separation of this fraction. Results indicate that both the porin-hexokinase gating system of the outer membrane and the calcium transporting complex of the inner membrane are present in the fraction which contains the contact sites.

Animals↗
PubMed1985

The role of hexokinase as a possible modulator of Ca2+ movements in isolated rat brain mitochondria.

The present study shows that in brain mitochondria the active calcium uptake and the sodium-dependent calcium efflux are modulated by the porin-bound enzyme hexokinase. The release of the enzyme, promoted by glucose-6-phosphate (G-6-P), under conditions which do not affect mitochondrial functions, is accompanied by a decrease of the rates of fluxes of the cation. This phenomenon is discussed and correlated with the formation of microcompartments between the inner and outer mitochondrial membranes, where the hexokinase-porin complex may constitute a regulating gate system for calcium.

Animals↗
PubMed1985

Studies on hereditary retinal degeneration. The rd gene in the mouse.

Stearic, oleic, linoleic, arachidonic, and docosahexaenoic acids can be detected regularly in the eyes and retinae of mice. During the period of maturation of the outer segments of the rod, the amount of each fatty acid increases, the most striking feature of which is the accumulation of docosahexaenoic acid in the retina, which might reflect the growth of rod outer segments. In rd/rd mice, fatty acid synthesis is reduced and the change characteristic of docosahexaenoic acid is absent. Analysis of the structure of outer segment disc membranes by the freeze fracturing technique, however, shows that the structure of the membrane is probably not affected by the rd gene.

Animals↗
PubMed1985

Cation-dependent reassembly of F0F1-ATPase in submitochondrial particles: evidence for a binding site for F1 on F0 in the absence of F6 and oligomycin sensitivity-conferring protein.

Bovine heart submitochondrial particles depleted of F1, OSCP (oligomycin sensitivity-conferring protein), and F6 require the presence of cations to rebind F1. Among the cations tested, NH4+, Cs+, and Rb+ were most efficient, followed by K+, Na+, Li+, Ca2+, and Mg2+. The extent of F1 binding approached that occurring upon supplementation with F6 and/or OSCP, and was similar to the F1 content of particles prior to depletion. In the absence of cations, F6 and/or OSCP were ineffective in promoting the binding of F1 to the depleted particles. The F1 bound to the particles in the presence of cations alone was completely insensitive to oligomycin. It remained bound to the particles after removal of the cation, and could be rendered partially (approximately 50%) or maximally (less than 80%) oligomycin-sensitive upon the subsequent addition of OSCP or of F6 and OSCP, respectively. The surface potential of the particles, as determined by microelectrophoresis, was screened by all cations tested, regardless of their ability to promote the binding of F1; this was in contrast to earlier findings with particles depleted of F1 only, where the ability of cations to promote the rebinding of F1 paralleled their efficiency to neutralize the surface charge of the particle membrane. It is concluded that the effect of cations on the binding of F1 to F1-, F6-, and OSCP-depleted particles is due to a specific interaction of the cations with certain segments or components of the membrane. The results suggest the existence of a binding site for F1 on F0 in addition to the binding site(s) provided by F6 and OSCP.

Ammonia↗
PubMed1985

Transport of Ca2+ and Mn2+ by mitochondria from rat liver, heart and brain.

The energy-dependent, respiration-supported uptake and the uncoupler- or Na+-induced release of Ca2+ and Mn2+ by mitochondria from rat liver, heart and brain were investigated, using as indicators radioisotopes (45Ca and 54Mn), proton ejection, oxygen consumption, nicotinamide nucleotide oxidation-reduction and, in the case of Ca2+, the metallochromic dye Arsenazo III. Ca2+ uptake in the presence of Pi was rapid in mitochondria from liver and brain, and less rapid in those from heart. Mn2+ uptake was much slower than that of Ca2+ in liver and heart, but only slightly slower in brain. When added together, Ca2+ accelerated the uptake of Mn2+, and Mn2+ retarded the uptake of Ca2+, by mitochondria from all three tissues. When Mn2+ was present during Ca2+ uptake, its own uptake remained accelerated even after Ca2+ uptake was terminated. Mg2+, which was not taken up, inhibited Ca2+ uptake by mitochondria from all three tissues, and, when present during Ca2+ uptake, accelerated the subsequent uptake of Mn2+. The uncoupler CCCP induced a release of both Ca2+ and Mn2+ from all three sources of mitochondria; yet, release of Mn2+ took place only in the absence of Pi. The release followed the same pattern as the uptake, i.e., Ca2+ accelerated the release of Mn2+ and Mn2+ retarded the release of Ca2+. Na+ induced a release of both Ca2+ and Mn2+ from heart and brain but not from liver mitochondria; again, Mn2+ release occurred only in the absence of Pi. The Na+-induced release of Ca2+ was inhibited by Mn2+, but the Na+-induced release of Mn2+ was not accelerated by Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Cation requirement for the reconstitution of oligomycin-sensitive ATPase by means of soluble F1-ATPase and F1-depleted submitochondrial particles.

Bovine heart submitochondrial particles depleted of F1 by treatment with urea ("F1-depleted particles') were incubated with soluble F1-ATPase. The binding of F1 to the particles and the concomitant conferral of oligomycin sensitivity on the ATPase activity required the presence of cations in the incubation medium. NH4+, K+, Rb+, Na+ and Li+ promoted reconstitution maximally at 40-74 mM, guanidinium+ and Tris+ at 20-30 mM, and Ca2+ and Mg2+ at 3-5 mM. The particles exhibited a negative zeta-potential, as determined by microelectrophoresis, and this was neutralized by mono- and divalent cations in the same concentration range as that needed to promote F1 binding and reconstitution of oligomycin-sensitive ATPase. It is concluded that the cations act by neutralizing negative charges on the membrane surface, mainly negatively charged phospholipids. These results are discussed in relation to earlier findings reported in the literature with F1-depleted thylakoid membranes and with submitochondrial particles depleted of both F1 and the coupling proteins F6 and oligomycin sensitivity-conferring protein.

Adenosine Triphosphatases↗
PubMed1982

Reconstitution in vitro of sulfobromophthalein transport by bilitranslocase.

Liposomes containing 150 mM KCl and 0.48 mM sulfobromophthalein have been prepared. The internal pH was set at 6.5, a value at which sulfobromopthalein is colorless. When brought to alkaline pH a certain amount of the dye is deprotonated and can be read spectrophotometrically as external sulfobromophthalein. Upon addition of Triton X-100 the membrane is dissolved and all sulfobromophthalein present in the preparation may be measured. Addition of bilitranslocase to such a preparation of liposomes causes the internal sulfobromophthalein to leave the internal compartment. The rate of this phenomenon may be followed directly and shown to be greatly accelerated by the addition of valinomycin. The latter finding indicates that sulfobromophthalein transport occurs in response to a membrane diffusion potential created by permeabilisation to K+ of liposomes brought about by valinomycin (uniport). The permeability change induced by bilitranslocase is specific and does not reflect an alteration of the normal impermeability of liposomes to small ions such as protons or Ca2+.

Animals↗
PubMed1980

The Ca2+-binding glycoprotein as the site of metabolic regulation of mitochondrial Ca2+ movements.

A change in the redox state of pyridine nucleotides such as that evoked by addition of oxaloacetate has been shown to promote Ca2+ efflux from Ca2+ pre-loaded respiring mitochondria. An affinity-chromatography-purified antibody preparation obtained against the mitochondrial Ca2+-binding glycoprotein inhibits the phenomenon. This finding suggests that the glycoprotein is involved also in the oxaloacetate-induced Ca2+ release. This conclusion is reinforced by the finding that Ca2+-binding glycoprotein shows four sites per molecule where the pyridine nucleotides may be bound. Binding of NAD+ occurs preferentially over the others and the binding shows positive cooperativity, indicating that the glycoprotein undergoes an allosteric change upon NAD+ binding. Interestingly, in addition, NAD+ lowers the affinity of the glycoprotein for Ca2+. The effect cannot be induced by NADH. Pyridine nucleotide phosphates, NADP+ and NADPH, are essentially not bound. The results are consistent with the view that the glycoprotein is the site of regulation of Ca2+ equilibration across the mitochondrial membrane and make it possible to conclude that the effector in the phenomenon is NAD+.

Animals↗
PubMed1979

The ability of the mitochondrial Ca2+-binding glycoprotein to restore Ca2+ transport in glycoprotein-depleted rat liver mitochondria.

Rat liver mitochondria may be subfractionated in sediment and supernatant fractions by swelling in the presence of EDTA and oxaloacetate. The sediment is largely depleted of the Ca2+-binding glycoprotein and its Ca2+-transporting activity may be as low as 10--20% of the starting value. Both the rate of Ca2+ uptake and the capacity to maintain a high Ca2+ concentration gradient across the membrane are depressed. Addition of an osmotic supernatant to the assay mixture may partially restore the original Ca2+-transporting ability. The active component in the supernatant is the Ca2+-binding glycoprotein. This is shown by the following facts: (a) the effect is enhanced by the addition of the purified glycoprotein to the supernatant; (b) precipitation of the glycoprotein from the supernatant by affinity chromatography-purified antibodies abolishes the stimulatory effect, and (c) in the presence of 130 microM Mg2+, the glycoprotein alone may restore fully the Ca2+-transporting ability of the particles. The maximal velocity is already reached at 0.1 microgram glycoprotein/mg mitochondrial protein.

Animals↗
PubMed1978

Isolation of a sulfobromophthalein-binding protein from hepatocyte plasma membrane.

This paper deals with the isolation and partial characterization of a protein capable of high affinity sulfobromophthalein-binding from liver plasma membrane. The purification involves acetone powder of a crude preparation of rat liver plasma membrane, salt extraction and purification through two chromatographic steps. Based on sulfobromophthalein binding, the process gives a yield of approximately 40%, with a purification of about 300 times with respect to the starting homogenate. The best preparation can bind more than 100 nmol sulfobromophthalein/mg protein. The protein behaves as a single species in dodecyl sulphate polyacrylamide gel electrophoresis, with an apparent molecular weight of 1.7 . 10(5). The molecule does not contain sugars. The dissociation constant of the protein . sulfobromophthalein complex has been found to be 4. 10(-6) M, a value in agreement with that of high affinity binding sites described on isolated liver plasma membrane.

Animals↗