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Biomedical subjects

L Masotti

Publications and source records attributed to L Masotti.

At least 73 records · Page 4Linked to original sources
PubMed1986

Myelin basic protein ability to organize lipid bilayers: structural transition in bilayers of lysophosphatidylcholine micelles.

Myelin basic protein isolated by a single step with the cationic detergent cethyltrimethylammonium bromide in a lipid-bound form is able to induce structural transition of lysophosphatydilcholine micelles into multi-laminar vesicles. This finding, observed through electron microscopy, is discussed in the light of the assumed ability of the basic protein to organize myelin lipids.

Animals↗
PubMed1986

DNA-4'-6-diamidine-2-phenylindole interactions: a comparative study employing fluorescence and ultraviolet spectroscopy.

DAPI is a drug that interacts with double-stranded nucleic acids, binding preferentially to A + T base pairs. The interaction is not intercalative, therefore providing a useful model for mimicking the effect of functional molecules in modifying specific sites, namely, A + T segments, of significance in gene expression. Knowledge of the nature of such interaction has been enriched by additional information obtained from comparative analysis of the data acquired by uv spectroscopy and fluorescence. Two classes of binding sites, defined by different apparent affinity constants and numbers of binding sites, are evident. All types of interaction are dependent on the nucleic acid/dye ratio and on the ionic strength of the medium.

Binding Sites↗
PubMed1986

On the complex nature of the antiviral activity of coumermycin A1: its interference with the replication of herpes simplex virus type 1.

The mechanism of inhibition of the replication of herpes simplex virus type 1 (HSV-1) by coumermycin A1 (CA1), an inhibitor of bacterial DNA gyrase, has been investigated. Concentrations of antibiotic slightly higher than those needed for 50% inhibition of viral growth were able to inhibit viral DNA synthesis in infected cells. This effect was accompanied by a depressed synthesis of viral polypeptides. Protein synthesis was also inhibited in uninfected cells, especially after long exposure to the drug, but not in a cell-free system. In vitro assays of highly purified HSV-1 DNA polymerase in the presence of the drug, provided evidence that the enzyme was a target of CA1. The viral polymerase was in fact inhibited by the antibiotic to an extent comparable to that of viral DNA synthesis in intact cells. In contrast, DNA polymerase alpha, the enzyme involved in chromosomal DNA replication, was relatively insensitive to CA1. The drug was also shown to bind to protein and to viral and cellular DNA.

Aminocoumarins↗
PubMed1986

Membrane alterations in cancer cells: the role of oxy radicals.

Membranes isolated from tumor cells present profound alterations in their composition, structural organization, and functional properties. In this study we have reported some of these alterations in microsomal and plasma membranes of hepatomas with different growth rate and degree of differentiation. The chemical parameters studied were the phospholipid-to-protein, the cholesterol-to-protein, and the cholesterol-to-phospholipid ratios and the fatty acid composition of the phospholipids. The physical parameters were the molecular order (static) and the fluidity (dynamic), determined, respectively, as the order parameter [P2] and the correlation time tau R of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The functional property investigated was the ability of the membranes to undergo superoxide-induced lipid peroxidation, determined as byproduct (malondialdehyde and lipid hydroperoxides) formation and as changes in the fatty acid acyl residues. Changes in the physical state of the membrane, induced by oxy radicals, were also monitored during lipid peroxidation. A study of the antioxidant activity of the tumor cell, in terms of oxy radical enzymatic defenses (superoxide dismutase, glutathione peroxidase and catalase) was also performed. The main results obtained are the following: hepatoma membranes possess a lower phospholipid content and a lower degree of fatty acid unsaturation; on the other hand, the cholesterol-to-phospholipid ratio is increased; the physical state appears characterized by an increased rigidity (increased molecular order of the lipids and decreased fluidity); the membrane peroxidizability is markedly depressed and its order parameter, in contrast to liver membranes, does not increase with exposure to the action of O2- radicals; and the oxy radical enzymatic defense mechanisms are decreased. All these alterations increase with increasing growth rate and dedifferentiation of the tumor. Considering all of the data, we are inclined to think that tumor membranes are altered structurally and functionally in part as the result of an oxy radical-induced damage that takes place in vivo under conditions of increased oxygen toxicity.

Animals↗
PubMed1985

Isolation and enzymatic characterization of the plasmalemma from bovine spermatozoa.

An improved method for the isolation of pure plasma and acrosomal membranes from bull spermatozoa is presented. Plasma membranes were isolated from the spermatozoa of bulls of different breeds, and some enzymatic activity, such as (Na+-K+) ATPase, Ca++ ATPase, Mg++ ATPase, alkaline and acidic phosphatases were assayed. Such enzymatic activity levels differ noticeably from those published by other authors, whose preparations were probably contaminated by other cellular components. Highly statistically significant differences of these activities have been found among the several breeds.

Acid Phosphatase↗
PubMed1985

A time-resolved fluorescence study of 4',6'-diamidine-2-phenylindole dihydrochloride binding to polynucleotides.

At phosphate/dye (P/D) ratios greater than 30 the quantum yield of 4',6'-diamidine-2-phenylindole dihydrochloride (DAPI)-DNA and DAPI-poly(d(A-T)) complexes was found to be 0.62 and 0.66, respectively. Contrary to earlier reports a fluorescence enhancement of DAPI-poly(d(G-C)) complexes was observed with a quantum yield of 0.22. Time-resolved fluorescence measurements of complexes with a P/D ratio of 150:1 indicate that there were three fluorescent components in DAPI-DNA complexes with lifetimes of 3.86, 1.79 and 0.13 ns. In DAPI-poly(d(A-T)) complexes the lifetimes were 3.91, 1.20 and 0.11 ns. Also, three components with lifetimes of 3.98, 0.87 and 0.12 ns were found in DAPI-poly(d(G-C)) complexes. At low P/D ratios (< 5) another binding form of DAPI was observed which was assigned to the interaction of one or more molecules of DAPI with one previously bound to DNA. It is concluded that DAPI does not exhibit A-T binding specificity and that at high P/D ratios there are two types of binding having similar binding constants.

Journal Article↗
PubMed1985

Fluorescence depolarization studies of melanosomal membranes from different sources.

In the present paper we report a comparative study of physical properties and biochemical composition of isolated melanosomal membranes extracted from bovine eyes and from an equine spleen melanoma. Some biophysical characteristics of such membranes were obtained by steady-state and time resolved fluorescence spectroscopy using DPH as fluorescent probe. By these methods we have measured both static fluorescence polarization and fluorescence lifetimes and from the experimental data we have calculated the rotational correlation times by Perrin's equation. Since dynamic and static parameters, such as fluidity and molecular order, can be determined by these methods, the results are discussed on the basis of the recent theories of the role of the biochemical composition in the molecular structure and properties of membranes.

Animals↗
PubMed1985

Interaction of papaverine with covalently closed DNA.

Cyclic nucleotides influence viral replication and papaverine, as an inhibitor of phosphodiesterase, also affects the replication of both DNA and RNA viruses through an increase in cAMP levels. Moreover in vitro papaverine affects neither protein synthesis nor several polymerases, while it inhibits DNA synthesis. Static fluorescence studies on the interaction of the drug with ColE1 plasmid covalently closed DNA indicate that the drug binds to the nucleic acid, probably by intercalation. A comparison between the binding characteristics of Papaverine and Actinomycin D is also reported.

Bacteriocin Plasmids↗
PubMed1984

Lipid peroxidation and fluidity of plasma membranes from rat liver and Morris hepatoma 3924A.

Plasma membranes isolated from the fast-growing, maximal-deviation, Morris hepatoma 3924A exhibit remarkable changes in lipid composition, lipid peroxidation and to some extent in the physical state with respect to rat liver plasmalemmas. A correlation appears to exist between the lower phospholipid: protein ratio, higher cholesterol: phospholipid ratio, lower rate of lipid peroxidation and decrease in fluidity in tumor plasma membranes.

Animals↗
PubMed1984

Nature of toxicity for chick embryo fibroblast cells of coumermycin A1 and its physico-chemical interactions with protein and nucleic acid.

The results reported in this paper describe the effects produced by the antibiotic Coumermycin A1 (CA1) on survival and metabolism of chick embryo fibroblast cells (CEF), and give a clue to the understanding of its toxicity. The drug acts primarily at the level of DNA and RNA synthetic enzymes; no effect on DNA superstructure is detectable at doses at which cytotoxicity is pronounced. A spectroscopic approach produced evidence that CA1 binds to DNA, RNA, chromatin components such as histones and to a structurally unrelated protein such as bovine serum albumin. Furthermore, CA1 behaves like a pure non-competitive inhibitor of lactic dehydrogenase, a ubiquitous enzyme not involved in nucleic acid metabolism. The interaction of CA1 with a wide range of macromolecules playing different biological roles is certainly relevant to its activity and adds a new insight into the mechanism of action of this antibiotic. These observations are also discussed in the light of the alleged role of CA1 as a specific inhibitor of DNA topoisomerase in eukaryotic cells.

Aminocoumarins↗
PubMed1984

Lipid composition, physical state, and lipid peroxidation of tumor membranes.

Studies were carried out on microsomes isolated from the highly differentiated (slow-growing) Morris hepatoma 9618A, on microsomes and plasma membranes from the poorly differentiated (fast-growing) Morris hepatoma 3924A, and rat liver used as control. The lipid composition (phospholipid and cholesterol content, degree of fatty acid unsaturation) and peroxidation of such membranes has been correlated with the order and fluidity of the membrane bilayer. The results indicate that substrate availability is the rate-limiting step in microsomal and plasma membrane lipid peroxidation of hepatoma 3924A. From diphenylhexatriene fluorescence depolarization measurements it appears that the changes in lipid composition cause an increase in the order of the lipid bilayer on going from the control to hepatoma 9618A and 3924A microsomes, while fluidity is virtually unchanged. Conversely, for similar chemical changes, in plasma membranes from hepatoma 3924A the order is nearly the same and there is a decrease in fluidity. The changes in the above parameters of tumor membranes might be partly related to the loss of protective enzymes against oxygen radicals. This is supported by the observation that inhibition of liver superoxide dismutase and glutathione reductase, by treatment of rats with diethyldithiocarbamate and chloroethyl nitrosourea, respectively, renders the microsomal membranes more resistant to lipid peroxidation in vitro.

Adenosine Diphosphate↗
PubMed1984

Different ability of novobiocin and coumermycin A1 to interact with nucleic acids.

The possibility of two structurally related antibiotics, Coumermycin A1 and Novobiocin, to interact with nucleic acids was investigated. Only Coumermycin A1 was able to form complexes with DNA showing an apparent affinity constant comparable to that of the interaction with ribosomal RNA. A binding specificity for A + T complementary and repeating sequences was also exhibited by Coumermycin A1. In view of the different behaviour of the two compounds some considerations are made on their mode of action; although they are acting on the same target enzymes in Escherichia coli, they may affect the functions of eukaryotic cells through a different mechanism not equally specific and probably distinct for each of the two antibiotics.

Aminocoumarins↗
PubMed1983

Supramolecular organization of lysophosphatidylcholine-packaged Gramicidin A.

Heat derived gramicidin A'/L-alpha-lysophosphatidylcholine complexes were separated on a sucrose gradient to form two fractions: Fraction A which had an approximately constant Gramicidin A' to phospholipid ratio of 8 to 10 lipid molecules per Gramicidin A' molecule and Fraction B which had a larger but variable ratio. Fluorescence and circular dichroism studies confirmed Fraction A to be a lipid-incorporated channel state. Electron microscopic studies, using uranyl acetate negative staining, showed fraction A to be a membranous state with the formation of bilayer vesicles, that is, the interaction of peptide and phospholipid micelles causes the lipid to reorganize into a bilayer structure. Freeze-fracture replicas of the channel incorporated state demonstrated the presence of a supramolecular organization of particles exhibiting a tendency to form rows with a 50-60 A periodicity along the row and with 70-80 A distance between rows. An idealized working model for the incorporated state is presented.

Biological Transport↗
PubMed1983

Gramicidin A induces lysolecithin to form bilayers.

Heat-induced association of Gramicidin A with lysolecithin micelles results in the formation of lipid bilayer structures. The capacity of the Gramicidin A peptide to transform the lysolecithin lipid structure from micelle to bilayer is considered in terms of molecular packing mechanisms and relevance to membrane processes in general. The resulting lipid-bilayer-packaged channel system has particular usefulness in characterizing channel structure and mechanism.

Chemical Phenomena↗
PubMed1982

Antioxidant activity of bull semen in relation with aging.

This paper reports on the findings of an antioxidant activity in whole semen from bull and its components, washed spermatozoa and seminal fluid. The antioxidant activity has been evaluated as the ability of semen or its components to inhibit the spontaneous autooxidation of epinephrine a pH 10, 2, which involves the production of superoxide radicals (0(2)). This preliminary study provides further evidence on the role of free radicals, which are well known to be dangerous to cellular life, and points to the need of a better understanding of the role of antioxidant activities as a cellular protective mechanism.

Aging↗
PubMed1982

Intermolecular interactions of gramicidin A' transmembrane channels incorporated into lysophosphatidylcholine lipid systems.

Fluorescence studies are reported on gramicidin A' incorporated into lysophosphatidylcholine phospholipid structures. The shift in the emission maximum during incorporation and the quenching of fluorescence by I- and by acrylamide of the incorporated state obtained after prolonged heating are consistent with the presence of the channel state comprised of two single-stranded beta 6 -helices associated head-to-head (formyl end-to-formyl end). The quantum yield for the incorporated state, when gramicidin A' is within the lipid matrix, is very low and indicates the occurrence of intermolecular Trp-Trp interactions. Possible interactions between channels within the lipid matrix are discussed utilizing Trp-Trp contacts.

Gramicidin↗