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G Trombetta

Publications and source records attributed to G Trombetta.

At least 19 recordsLinked to original sources
PubMed1992

A computer-assisted automatic method for myelinated nerve fiber morphometry.

This paper describes a computer-assisted automatic method developed for myelinated nerve fiber morphometry. IBAS image analysis system was used. One-micron thick sections of sural nerve were stained with p-phenylenediamine. Dark myelin sheaths, standing out against a pale background, were identified by a binary transformation of the computer-stored image. Different parameters of the fibers as well as of the axons can be measured. The automatic system allows operator-interactive manipulation, if required, to avoid inclusion of wrong histologic structures. A large spectrum of statistics facilities are available. We performed a comparison between automatic and semi-automatic analysis. Measurements resulted virtually overlapping, but time was three to four times shorter with automatic procedure. The method here described is accurate and reliable, and permits economy of time and effort.

Biopsy↗
PubMed1991

Binding of alpha-actinin to F-actin or to tropomyosin F-actin is a function of both alpha-actinin concentration and gel structure.

We have studied by electron microscopy as well as by measurements of low shear viscosity, rigidity and binding, the effect of alpha-actinin on the gel formed at 37 degrees C with F-actin and with tropomyosin-decorated F-actin. Contrary to previous reports in the literature, alpha-actinin at nanomolar concentrations is an efficient actin gelling protein, even at 37 degrees C, provided that the concentration of actin (or of tropomyosin-decorated F-actin) is low (1.2-2.4 microM). The binding of alpha-actinin to F-actin, as a function of actin concentration, is anomalous. The amount of bound alpha-actinin increases when actin concentration increases from 0 to 1.2 microM but does not change significantly when actin concentration is further increased up to 48 microM. A similar result is obtained with tropomyosin-decorated F-actin. These observations can be explained by an hypothesis that binding is a function of the alpha-actinin - F-actin association constant as well as of the rigidity of the gel. When the concentration of actin increases, the rigidity of the gel also increases and more work is required to bring two actin filaments to the reaction distance with alpha-actinin and, consequently, a larger alpha-actinin concentration is required to attain the same ratio of bound alpha-actinin to actin monomers in the filaments.

Actinin↗
PubMed1990

The actin gelling activity of chicken gizzard alpha-actinin at physiological temperature is triggered by water sequestration.

At 37 degrees C, in the presence of 6% (w/v) polyethylene glycol 6000, 30 nM alpha-actinin from chicken gizzard induces the gelation of 12 microM actin. Static measurement shows that the addition of 30 nM alpha-actinin increases the rigidity of the system from 23.5 to 54 dynes/cm2. According to the theory of osmoelastic coupling, also large additives, such as the proteins of the cell sap, are able to cause an osmotic stress equivalent to that caused by polyethylene glycol. We thus conclude that, in vivo, alpha-actinin acts as an actin gelling protein.

Actinin↗
PubMed1990

Divergent effects of filamin and tropomyosin on actin filaments bundling.

Filamin increases and tropomyosin decreases the susceptibility of F-actin to form bundles of filaments in the presence of polyethylene glycol 6000. The two proteins, which are located in the leading edge and in the internal part of the cell, respectively, are thus likely to display divergent effects on the microfilaments into bundles transition in these two areas of the cell.

Actin Cytoskeleton↗
PubMed1990

Microfilament gel rigidity cooperates negatively with the binding of actin gelling proteins.

At 37 degrees C, in the presence of 0.1 M KC1 and 2 mM MgCl2, the binding of alpha-actinin to F-actin increases with the concentration of alpha-actinin but not with the concentration of F-actin. This implies that binding is determined by additional factors, beside the alpha-actinin - F-actin association constant. We propose that one of these factors is the rigidity of the gel, which cooperates negatively to the binding by increasing the work needed to bring two actin filaments at the reaction distance with alpha-actinin.

Actin Cytoskeleton↗
PubMed1989

Substoichiometric concentrations of ATP-G-actin are required to anneal actin polymerized by calcium ions.

At 3 degrees C and pH 7.0, the addition of 40 nM ATP-G-actin to F-actin (12 microM as the monomer), polymerized in the presence of 4 mM CaCl2, determines a substantial and rapid increase of the viscosity of the solution, which is accompanied by the incorporation of the ATP-G-actin added into the polymer. The hypothesis that the presence of ATP-actin at the filament end(s) promotes the annealing reaction is substantiated by the finding that, after the addition of ATP-G-actin, the average filament length is increased. This finding is relevant, not only because it provides evidences in favour of the existence of annealing but also because it shows that the concentration of ATP-G-actin influences the filaments length distribution through a mechanism different from the elongation reaction.

Actins↗
PubMed1987

Fructose bisphosphate aldolase from rabbit muscle. A jump in the van't Hoff plot accompanies the onset of half of the sites' reactivity.

In 40% ethylene glycol, gamma/2 = 0.11 and pH* 8.2, fructose 1,6-bisphosphate aldolase from rabbit muscle undergoes a transition: above 3 degrees C it displays 4 equivalent dihydroxyacetone phosphate binding sites, below -1 degree C the sites decrease to 2. The dissociation constant of the aldolase-dihydroxyacetone phosphate complex decreases from 10 microM at 3 degrees C to 2.65 microM at -1 degree C, its van't Hoff plot being linear between -1 degree C and -13 degrees C. The rate of the detritiation of the aldolase-(3S)-[3-3H]dihydroxyacetone phosphate complex is strongly influenced by temperature. In 40% ethylene glycol, gamma/2 = 0.01 and pH* 8.2, the apparent rate constant is 7.6 sec-1 at -5 degrees C and 0.012 sec-1 at -24 degrees C. The Arrhenius plot is linear between -5 degrees C and -24 degrees C.

Animals↗
PubMed1985

Effects of temperature on actin polymerized by Ca2+. Direct evidence of fragmentation.

When the temperature is lowered from 20 to 4 degrees C, the specific viscosity of actin polymerized in the presence of either 4 mM-CaCl2 or 2 mM-MgCl2, but not of actin polymerized in the presence of 90 mM-KCl, is decreased by 50% in the absence of free ATP. Addition of ATP restores the viscosity of the actin polymerized by Mg2+, but not that of actin polymerized by Ca2+, to the original value. The effect of temperature on actin polymerized in the presence of Ca2+ is due to (a) polymer-into-monomer conversion, (b) latero-lateral aggregation of filaments, and (c) fragmentation of the filaments. Fragmentation, as demonstrated by fractional centrifugation and electron microscopy, was the most important of these.

Actins↗
PubMed1979

Fructose-1,6-bisphosphate aldolase from rabbit liver. Reaction mechanism and physiological function.

Liver and muscle aldolase display similar reaction mechanisms. Both the enzymes, by reacting with dihydroxyacetone phosphate, form an acid-labile intermediate which is in rapid equilibrium with an eneamine intermediate. Differences are found in the equilibrium concentration of the acid-labile intermediate, which represents approximately 25% of the total intermediates in the liver (this paper) and 60% in the muscle enzyme [E. Grazi and G. Trombetta, Biochem. J. 175, 361 (1978)] and in the rate of formation of the eneamine intermediate which is much slower in the liver enzyme. Furthermore, with liver aldolase, the rate by which the C-3H bond of dihydroxyacetone phosphate is cleaved is increased by 60 times in the presence of glyceraldehyde 3-phosphate. This, mechanistically, indicates that glyceraldehyde 3-phosphate is bound to the enzyme before the formation of the eneamine from dihydroxyacetone phosphate, and, physiologically, that in liever aldolase the gluconeogenetic activity is favoured over the glycolytic activity.

Animals↗
PubMed1978

A new intermediate of the aldolase reaction, the pyruvaldehyde-aldolase-orthophosphate complex.

Fructose 1,6-bisphosphate aldolase from rabbit muscle forms by reaction with dihydroxyacetone phosphate a pyruvaldehyde-aldolase-orthophosphate complex that is in equilibrium with the eneamine intermediate. The new intermediate accumulates in two phases. The first one is practically complete in 40ms, and the second occurs with an apparent first-order rate constant of 4.6 +/- 0.5s-1. The new intermediate breaks down slowly with the release into the medium of pyruvaldehyde and Pi. The rate of the spontaneous release is higher at acidic than at neutral pH.

Aldehydes↗