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Biomedical subjects

I Pasquali-Ronchetti

Publications and source records attributed to I Pasquali-Ronchetti.

At least 55 records · Page 3Linked to original sources
PubMed1982

Multiple supramolecular structures formed by interaction of actin with protamine.

When protamine is added to actin, different supramolecular structures are formed depending on the molar ratio of the two proteins and of the ionic strength of the medium. At low ionic strength, and going from a molar ratio of protamine to G-actin of 4:1, 2:1 and 1:1, globular aggregates are first converted into extended structures and then to long threads in which the constituent ATP-G-actin is rapidly exchangeable with the actin of the medium. At high ionic strength {Tyrode [(1910) Arch. Int. Pharmacodyn. Ther.20, 205-212] solution}, starting from G-actin and protamine in the 1:1 molar ratio, long ropes are formed that can be resolved into intertwining filaments of 4-5nm diameter. The addition of protamine in a 1:1 molar ratio to a solution of F-actin in Tyrode solution causes the breakage of the actin filaments, which is also revealed by the decrease of the viscosity of the solution and the formation of ordered latero-lateral aggregates. The structures formed by reaction of protamine with G-actin can be separated from free G-actin and protamine by filtration through 0.45mum-pore-size Millipore filters. This technique has been exploited to study the exchange reaction between free actin and the actin-protamine complexes. For these studies the 1:1 actin-protamine complex formed at low ionic strength and the 2:1 actin-protamine complex formed in the presence of 23nm-free Mg(2+) have been selected. In the first case the exchange reaction is practically complete in the dead time of the experiment (20s). In the second case, where the complex operates like a true ATPase, the rate of the exchange is initially comparable with the rate of the ATP cleavage. Later on, however, the complex undergoes a change and the rate of the exchange between free actin and the actin bound to protamine becomes lower than the rate of the ATPase reaction. It is proposed that the ATP exchanges for ADP directly on the G-actin bound in the complex.

Actins↗
PubMed1982

Biochemical heterogeneity of skeletal-muscle microsomal membranes. Membrane origin, membrane specificity and fibre types.

1. Microsomes were isolated from rabbit fast-twitch and slow-twitch muscle and were separated into heavy and light fractions by centrifugation in a linear (0.3-2m) sucrose density gradient. The membrane origin of microsomal vesicles was investigated by studying biochemical markers of the sarcoplasmic-reticulum membranes and of surface and T-tubular membranes, as well as their freeze-fracture properties. 2. Polyacrylamide-gel electrophoresis showed differences in the Ca(2+)-dependent ATPase/calsequestrin ratio between heavy and light fractions, which were apparently consistent with their respective origin from cisternal and longitudinal sarcoplasmic reticulum, as well as unrelated differences, such as peptides specific to slow-muscle microsomes (mol.wts. 76000, 60000, 56000 and 45000). 3. Freeze-fracture electron microscopy of muscle microsomes demonstrated that vesicles truly derived from the sarcoplasmic reticulum, with an average density of 9nm particles on the concave face of about 3000/mum(2) for both fast and slow muscle, were admixed with vesicles with particle densities below 1000/mum(2). 4. As determined in the light fractions, the sarcoplasmic-reticulum vesicles accounted for 84% and 57% of the total number of microsomal vesicles, for fast and slow muscle respectively. These values agreed closely with the percentage values of Ca(2+)-dependent ATPase protein obtained by gel densitometry. 5. The T-tubular origin of vesicles with a smooth concave fracture face in slow-muscle microsomes is supported by their relative high content in total phospholipid and cholesterol, compared with the microsomes of fast muscle, and by other correlative data, such as the presence of (Na(+)+K(+))-dependent ATPase activity and of low amounts of Na(+)-dependent membrane phosphorylation. 6. Among intrinsic sarcoplasmic-reticulum membrane proteins, a proteolipid of mol.wt. 12000 is shown to be identical in the microsomes of both fast and slow muscle and the Ca(2+)-dependent ATPase to be antigenically and catalytically different, though electrophoretically homogeneous. 7. Basal Mg(2+)-activated ATPase activity was found to be high in light microsomes from slow muscle, but its identification with an enzyme different from the Ca(2+)-dependent ATPase is still not conclusive. 8. Enzyme proteins that are suggested to be specific to slow-muscle longitudinal sarcoplasmic reticulum are the flavoprotein NADH:cytochrome b(5) reductase (mol.wt. 32000), cytochrome b(5) (mol.wt. 17000) and the stearoyl-CoA desaturase, though essentially by criteria of plausibility.

Animals↗
PubMed1981

Raman spectroscopic investigations on conformational changes induced by some phenol derivatives on phospholipid membranes.

Some phenol derivatives which uncouple oxidative phosphorylation in mitochondria alter the dipalmitoylphosphatidylcholine membrane structure in the same way that elevating the temperature does. Below the transition temperature, they disorder the membrane gel-phase by inducing the pretransition situation at concentrations within significant biological limits. When the temperature is higher than Tm, their effect on the membrane structure is negligible. The comparison of these phenol derivatives having uncoupling activity with a phenol derivative which does not have such activity demonstrates that the latter does not induce a similar physical effect.

2,4-Dinitrophenol↗
PubMed1981

Pseudoxanthoma elasticum. Biochemical and ultrastructural studies.

Ultrastructural and biochemical studies of the dermis from patients with pseudoxanthoma elasticum are described. Elastin fibers showed mineral deposits that were associated with an elastin material exhibiting altered affinity for the electron microscopical stains and altered ultrastructural organization. In the most affected patient the elastin was shown to be increased and to have an abnormal amino acid composition. In some patients the collagen fibers were laterally fused. The ground substance was increased as evidenced by electron microscopy and confirmed by a slight increase in uronic acids, hexosamines, and neutral sugars.

Amino Acids↗
PubMed1980

Ultrastructural and biochemical changes induced by progressive lipid peroxidation on isolated microsomes and rat liver endoplasmic reticulum.

Ultrastructural and biochemical alterations induced by progressive lipid peroxidation on rat liver endoplasmic reticulum and on isolated microsomes have been studied. Lipid peroxidation was followed by measuring the content of malonaldehyde and similar thiobarbituric acid-reacting substances in the control specimens and in specimens in which lipid peroxidation was stimulated by CCl4 or other prooxidant systems. Lipid peroxidation induced a remarkable decrease in aminopyrine demethylase activity and in the cytochrome P-450 content both in vivo and in vitro. Parallel to these observations, alterations in the assembly of the membranes of isolated rat liver microsomes and of in situ endoplasmic reticulum were followed by electron spin resonance and electron microscopy. Electron spin resonance revealed changes in the resonance spectra interpreted as solubilization of cytochrome P-450 from the membrane. Electron microscopy on fixed and sectioned, negatively stained and freeze-fractured specimens revealed membrane alterations that were progressive with time of peroxidation. These alterations consisted of: (1) increased membrane deformability; (2) local and progressive breakages on the membranes; and (3) loss of intramembranous particles on both fracture faces of the membranes. The results obtained with the different techniques are compared and discussed in light of the importance of the lipid environment for the structure and function of biologic membranes.

Aminopyrine N-Demethylase↗
PubMed1977

Biochemical lesions of respiratory enzymes and configurational changes of mitochondria in vivo. II. Early ultrastructural modifications correlated to the biochemical lesion induced by fluoroacetate.

Correlative biochemical and electron microscopic alterations were observed in chick embryo myoblasts in vitro after treatment with fluoroacetate. Fluoroacetate poisoning caused an increase of citrate and a decrease of ATP in the cultures. Cell respiration was only slighly impaired by fluoroacetate in the first 10 min but was inhibited to 30% one hour after exposure to the poison. Fluoroacetate did not affect oxidative phosphorylation. The evidence suggests that fluoroacetate was transformed in myoblasts into fluorocitrate which inhibited the mitochondrial-bound aconitate hydratase as in adult tissues. Ultrastructural changes in the majority of the fluoroacetate-treated cells were observed. Very few myoblasts appeared unaffected by the poison. Mitochondria were specifically altered. The early changes occurred in the mitochondrial matrix where the inhibited enzyme is known to be located and were followed by modifications in the configuration and structure of cristae. Exogenous fluorocitrate caused ultrastructural changes in the mitochondria similar to that provoked by fluoroacetate. The localization of the early change in the mitochondrial matrix and the evaluation of the structural modifications suggest a correlation between the biochemical lesion, i.e. the inhibition of aconitate hydratase, and the change revealed in the mitochondrial structure containing the inhibited enzyme.

Aconitate Hydratase↗
PubMed1976

Banded figers in high temperature coacervates of elastin peptides.

Electron micrographs of negatively stained coacervates of the synthetic polypentapeptide of propoelastin and of alpha-elastin exhibit banded fibers when the coacervates are formed, stained, and dried at temperatures greater than 50 degrees. This apparent increase in order occurs at the same temperature as an increase in order in aqueous solution and as a change in the volume expansion coefficient of fibrous elastin.

Elastin↗
PubMed1975

Plasma lipoproteins in rats with experimental biliary obstruction. I. A chemical study.

Acute biliary obstruction in the rat is associated with striking alterations of the plasma level and the physico-chemical properties of plasma lipoproteins. 1. The level of very low density lipproteins (VLDL) in plasma increases from 2 to 3 fold. The chemical composition of VLDL is characterized by a high content of phospholipids and cholesterol and by a diminution of the relative content of triacylglycerols and protein. On cellulose acetate electrophoresis, VLDL show a beta-mobility. 2. The plasma concentration of low density lipoproteins (1.019--1.063 g/ml, LDL2) increases several fold above the control level. Phospholipids and unesterified cholesterol are the major components of this fraction which contains only a minute amount of cholesteryl ester (4%) and triacylglycerols (10%). LDL2 contain a component which migrates to the cathode in 1% agar gel electrophoresis. Separation of LDL2 by gel filtration on 2% agarose column results in the identification of three subfractions. Subfraction I contains a large proportion of cholesterol and triacylgylcerols, subfraction II is rich in unesterified cholesterol and phospholipids whereas subfraction III has a chemical composition fairly similar to that of the control LDL2. 3. The level of high density lipoproteins (HDL) also increases after bile duct ligation. The chemical composition of HDL2 (1.063-1.125 g/ml) is characterized by a high content of unesterified cholesterol and phospholipids and by a remarkable reduction in the content of cholesteryl esters and protein.

Animals↗