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A Sobota

Publications and source records attributed to A Sobota.

At least 37 records · Page 2Linked to original sources
PubMed1987

Polyamine metabolism in Acanthamoeba: polyamine content and synthesis of ornithine, putrescine, and diaminopropane.

Five polyamines which could be separated by high performance liquid chromatography were found in Acanthamoeba castellanii (strain Neff). These included in order of decreasing abundance: 1,3-diaminopropane, spermidine, spermine, norspermidine, and putrescine. Only diaminopropane and norspermidine had been found previously. Spermine was present in cultures grown in broth, but not in defined medium. Radioactive substrates were used to establish that putrescine was synthesized by decarboxylation of ornithine, ornithine was synthesized from arginine or citrulline, and diaminopropane was synthesized from spermidine. The presence of ornithine decarboxylase (EC 4.1.1.17), arginase (EC 3.5.3.1), and urease (EC 3.5.1.5) and the absence of arginine decarboxylase (EC 4.1.1.19) were established. A scheme for polyamine biosynthesis in A. castellanii is proposed.

Acanthamoeba↗
PubMed1985

Displacement of cell-surface associated calcium inhibits phagocytosis and Ca-ATPase activity in amoeba.

Displacement of calcium from the cell surface region was observed in cells treated with either chlorpromazine or reserpine with chlorotetracycline being used as a calcium-fluorescent probe. The drugs also significantly inhibit the intensity of phagocytosis and Ca-ATPase activity. The possible role of Ca associated with the cell surface region in regulation of both phagocytosis and Ca-ATPase was discussed.

Amoeba↗
PubMed1985

Subplasmalemmal calcium-binding microregions in Acanthamoeba.

Acanthamoeba cells, fixed with glutaraldehyde supplemented with calcium ions, show Ca-dependent, electron-dense deposits (CaDD) at the cytoplasmic surface of the plasma membrane. The formation of CaDD is stimulated by pre-incubation and fixation of the cells in the presence of ATP. Chemical analysis of the trichloroacetic acid extracts of CaDD-containing cells demonstrates that adenosine monophosphate, pyrophosphate and inorganic phosphate are probably the compounds involved in the formation of CaDD. Treatment of CaDD-containing cells with exogenous phosphatase evokes the disappearance of electron-dense material and a fine fibrillar network can be observed inside the 'empty' CaDD. The ability to restore CaDD in the presence of calcium ions with either pyrophosphate or orthophosphate confirms the suggestion that calcium/phosphate salts may be deposited in special subplasmalemmal calcium-binding microregions.

Adenosine Diphosphate↗
PubMed1984

Correlation between potassium and phosphorus content and their nonuniform distribution in Acanthamoeba castellanii.

Biologically important elements: K, Na, Mg, Ca, Cl, P, and S were analyzed in Acanthamoeba castellanii. A higher potassium content, as compared with other cations, was detected. Total content of the cation-forming elements: K, Na, Mg, and Ca was ca. 360 mmoles/kg dry weight of the cells. Phosphorus content was estimated as 492 mmoles/kg dry weight. Content of chlorine, a basic cellular anion, was 173 mmoles/kg dry weight. The low level of chlorine appears not the be sufficient to balance all the cations in Acanthamoeba. Distribution of potassium in Acanthamoeba cells was nonuniform and similar to that of phosphorus as shown by X-ray microanalysis technique. Quantitative correlation between phosphorus and potassium as well as the similar distribution of these elements suggests that in Acanthamoeba phosphorus is an essential anion which, being nonuniformly distributed in the cell, determines also a nonuniform distribution of potassium.

Amoeba↗
PubMed1984

Calcium binding sites in the insect polytrophic egg vesicles as possible markers of the route of inflow of calcium.

Calcium binding sites were revealed in the polytropic egg vesicles of Galleria mellonella (Lepidoptera) by fixation of the ovariole with glutaraldehyde in the presence of excess of calcium. Calcium dependent deposits appeared in the mitochondrial matrix in cells of the epithelial sheath and of the follicular epithelium. The deposits were also seen in the extracellular space around the follicular epithelial cells and around the trophocytes , at the oolemma, and in the coated vesicles of the oocytes at the stage of vitellogenesis. On the other hand, the deposits were not detected in the mitochondria of the trophocytes and the oocytes. Considering the high content of calcium in the insect oocyte ( Przel ecka et al. [17]) the possible route of entry of calcium to the oocyte is discussed on the basis of distribution of the visualized calcium binding sites.

Animals↗
PubMed1982

Capillary resistance to flow of hardened (diamide treated)red blood cells (RBC).

Pressure-flow curves for control and hardened (diamide treated) human RBC's were obtained in capillaries of the isolated rat mesentery, in order to evaluate resistance to flow of hardened RBC's. Blood vessels were maximally dilated by an infusion of 10(-5) mol/l acetylcholine and isoprenaline and perfused with freshly collected human RBC's as well as with RBC's hardened by a treatment (hct 40%; pH 8.0; 37 degree C) with 0.5 mmol/l or 1.5 mmol/l diamide, respectively, suspended in Albumin (0.05%) - Ringer solution. The mesentery was perfused via a hydrostatic pressure reservoir. Arterio-venous pressure difference was varied from 4-10 kPa, and corresponding arteriolo-venular pressure gradients changed from about 200-500 Pa/mm. No significant difference in resistance to flow was observed between control and diamide treated cells over the whole pressure range. However, the flow through the microvascular bed was inhomogeneous upon perfusion with diamide treated cells, caused by a deceleration and stoppage of the cells at capillary narrowing (ratio of cell to vessel diameter greater than 2). The time of stagnation increased with decreasing pressure gradient.

Animals↗
PubMed1982

Growth phase dependent alterations in the surface coat of Acanthamoeba castellanii.

Application of ruthenium red, cationized ferritin and concanavalin A to exponentially growing trophozoites reveals on their plasma membrane negatively charged surface coat bearing sugar residues. In the coat of trophozoites from advanced stationary growth phase no sugar residues can be visualized. In mature cysts the external layer of their wall is negatively charged, however, on their protoplast surface no terminals reacting with the 2 polycations, or with concanavalin A can be revealed, even though the penetration of the reagents has been ensured by enzymatic impairing of the cyst wall. The results are confronted with the known facts concerning alterations of physiological properties of plasma membrane occurring during the life cycle of Acanthamoeba.

Amoeba↗
PubMed1981

Developmental changes in the localization of calcium binding sites in Acanthamoeba castellanii.

Vegetative cells of Acanthamoeba castellanii have the ability to bind calcium on the plasma membrane in form of the electron-dense deposits. The appearance of the deposits depends on the age of Acanthamoeba culture. In 24-h-old culture the deposits are very small, with diameter of 26 nm. During aging of culture, at both logarithmic and stationary growth phases, the diameter of deposits is larger (70-80 nm), while the deposits are localized only on the plasma membrane. During differentiation of Acanthamoeba cells into cysts electron-dense deposits with a diameter of about 170 nm appear in the mitochondria, whereas no deposits are observed on the plasma membrane. However, at the first stage of differentiation electron-dense material together with extruded membraneous fragments are also observed outside of some newly-formed young cysts. These results suggest that in Acanthamoeba cells, depending on the stage of life cycle, either plasma membrane or mitochondria may be involved in storage of excess cellular calcium.

Amoeba↗
PubMed1981

Heterogenous distribution of potassium and phosphorus in Acanthamoeba castellanii.

Using x-ray microanalysis technique the distribution of potassium, phosphorus and sulphur was analysed in Acanthamoeba castellanii cells. Distribution of potassium was nonuniform; the high level of the element was observed in the cortex region of these cells. Distribution of phosphorus was shown to be similar to that of potassium, whereas sulphur was rather uniformly distributed.

Amoeba↗
PubMed1981

Visualization of calcium-binding sites at plasma membrane of shock-frozen Acanthamoeba cells.

Electron-dense deposits appear at the protoplasmic side of plasma membrane in Acanthamoeba log-phase cells when fixed either with glutaraldehyde or formaldehyde supplemented with Ca2+. Similar deposits appear when the cells are preloaded with Ca2+ and thereafter shock-frozen and prepared for electron microscopic examination by freeze-substitution technique. This suggests that their formation reflects the presence of a physiologically active system involved in capturing excess of inflowing calcium.

Amoeba↗
PubMed1981

A RNA helix-destabilizing protein is a major component of Artemia salina nuclear ribonucleoproteins.

A major component of 30S heterogeneous nuclear ribonucleoprotein (hnRNP) particles from Artemia salina is HD40, a protein that has been characterized as a RNA helix-destabilizing protein [Marvil, D. K., Nowak, L. & Szer, W. (1980) J. Biol. Chem. 255, 6466-6472; Nowak, L., Marvil, D. K., Thomas, J. O., Boublik, M. & Szer, W. (1980) J. Biol. Chem. 255, 6473-6478]. HD40 binds to and disrupts the secondary structure of nuclear RNA fragments isolated from 30S hnRNP with a stoichiometry of one protein per 10-12 nucleotides. The addition of HD40 in excess of this ratio results in the formation of bead-like HD4-nuclear RNA complexes that are similar in properties and appearance to native 30S hnRNP particles. The heterogeneous nuclear RNA (hnRNA) in the HD40-hnRNA complexes is unstacked and unfolded to about the same extent as the RNA in the native 30S hnRNP particles. HD40 is strikingly similar in molecular weight (40,000) and amino acid composition (no cysteine, high glycine, presence of dimethylarginine, and blocked NH2 terminus) to eukaryotic hnRNP proteins isolated from many cell types. HD40 can be separated into three isoelectric species with basic pIs, which appears to be posttranslational modifications of a single polypeptide chain.

Animals↗
PubMed1980

Calcium content and distribution in egg vesicles of Galleria mellonella (Lepidoptera) as determined by X-ray microanalysis.

In egg vesicles of Galleria mellonella (Lepidoptera) electron microprobe analysis reveals calcium in concentrations of 9 and 3 mmoles per 1,000 g tissue wet weight in oocyters and accompanying trophic cells, respectively. This high average level of calcium characterizes both pre- and postvitellogenic oocytes, but the distribution of calcium is not uniform. In postvitellogenic vesicles the central area of the ooplasm shows a higher content of Ca than peripheral one, what may be correlated with the distribution of mature yolk platelets within the ooplasm.

Animals↗
PubMed1980

Effect of a membrane-stabilizing compound on calcium binding to the plasma membrane of Acanthamoeba castellanii.

Binding of calcium ions at the plasma membrane was studied in Acanthamoeba cells pretreated with ZIMET 3164, a benzimidazole nitrogen mustard derivative, which is known to show a potent immunosuppressive action combined with a membrane-stabilizing effect in mice. For reference, 2 compounds were applied: ZIMET 3393 (Cytostasan¿), another benzimidazole mustard derivative, which exerts only a moderate membrane effect and acts as a strong cytostatic, and ZIMET 176/68, a barbituric acid derivative, which acts as an inhibitor of humoral immune responses but without membrane-stabilizing effect. Application of any of the 3 compounds does not reduce the appearance of calcium binding sites, visualized by means of ultracytochemical reaction, notwithstanding their different action in the mammalian organism. On the contrary, it was estimated by morphometric analysis that the number of Ca-dependent deposits was augmented after treatment with low doses of any of the 3 compounds, what seems to be connected with the induced metabolic disturbances in low molecular phosphates level. High doses and/or prolongation of treatment of the cells resulted in diminution of the number of deposits and induces profound disturbances in cell ultrastructure, probably due to the toxic action of the applied doses. In these cases, band-like structures crosslinking the two leaflets of the plasma membrane may be observed; it is suggested that they represent integral membrane proteins.

Amoeba↗
PubMedDate not supplied

Interaction of annexins IV and VI with phosphatidylserine in the presence of Ca2+: monolayer and proteolytic study.

Annexins, Ca2+- and phospholipid-binding proteins are known to bind to artificial and biological membranes in a calcium-dependent manner. However, the precise mechanism of the annexin-membrane interactions still remains to be studied in detail. In this paper we describe the results of studies on the interactions of the annexin/Ca complexes with phospholipids, obtained by the Wilhelmy balance method of assessing the surface pressure of a phospholipid monolayer. We show that the annexin IV/Ca as well as annexin VI/Ca complexes significantly reduce the surface pressure of a phosphatidylserine monolayer, when its initial value is close to collapse pressure. The effect is highly specific for monolayers composed of phosphatidylserine and strongly sensitive to pH and ionic strength. The most pronounced changes have been observed at pH 7.0-7.5, at a protein/Ca molar ratio of 1:2 for annexin IV and 1:4 for annexin VI. In the presence of sodium chloride at concentrations exceeding 400mM this effect was almost completely abolished. The obtained results point to the mainly electrostatic character of the annexin/phosphatidylserine interactions. In addition, using large multilamellar lipid vesicles and serine proteases, we demonstrate that annexins, when bound in a ternary complex with phospholipids and calcium ions, are partially protected against proteolysis. Our observation that annexin molecules, complexed with calcium ions, are protected against proteolytic attack in the presence of PS liposomes does not have to be necessarily explained in terms of partial penetration of protein within the membrane bilayer.

Animals↗