The effect of concanavalin A on egestion of food vacuoles in Tetrahymena

The ability of concanavalin A (conA) to disrupt food vacuole elimination at the cytoproct of Tetrahymena pyriformis, strain GL-C, was investigated using fluorescence microscopy and thin section electron microscopy. ConA was found to induce "tails" in Tetrahymena. These tails were specifically stained by fluorescent conA. Thin section observations of conA-treated cells revealed that these tails were the result of abnormal egestion of food vacuole contents at the cytoproct. Tail formation appears to result from an inhibition of endocytosis of food vacuole membrane during egestion. Instead, the food vacuole membrane appears to be cast out of the cell, along with the contents of the vacuole. The mechanism of this inhibition may be related to an apparent absence of microtubules or microfilamentous mat in the cytoproct region of conA-treated cells. Although conA is ingested into food vacuoles in large amounts, conA appears to affect endocytosis only from outside the cell; ingested conA does not appear to be effective. ConA may exert its influence by binding to the cytoproct region. The ability of conA to induce tail formation is inhibited by sugars specific to it. Numerous membranous vesicles are found in association with the oral cilia and cytoproct region of conA-treated cells. These vesicles may be the conA-binding material reported to be secreted by Tetrahymena.     

Structural changes caused by thyrotropin in thyroid cells and in liposomes containing reconstituted thyrotropin receptor

Thyrotropin causes a rapid and significant increase in the fluorescence polarization of DPH when this hydrophobic probe is incorporated into a strain of functioning rat thyroid cells (FRTL5). This increase is ligand-specific and is not related to cAMP production. The phenomenon seems to reflect the interaction of thyrotropin with the glycoprotein component of its membrane receptor, as suggested by experiments in which thyrotropin causes increases in DPH fluorescence polarization in liposomes embedded with this receptor component but not with gangliosides. A strain of nonfunctioning rat thyroid cells (FRT), exhibiting no reactivity with monoclonal antibodies to the glycoprotein component of the thyrotropin receptor, requires two orders of magnitude higher concentrations of thyrotropin to exhibit a comparable phenomenon.     

Sensitivity to values of the rate constants in a neurochemical metabolic model

Equations were derived for the instantaneous relative sensitivities of reaction rates (controllability indices) and metabolite concentrations (response indices) to perturbations in the values of rate constants and were used to analyze the behavior of a model of in vivo glutamate metabolism in rat brain. Controllabilities of reversible reactions were found to increase as the values of the corresponding rate constants (i.e., the rate of approach to equilibrium) increased. Response indices generally declined with the metabolic distance between the metabolite and the rate constant, but they were unexpectedly high for reversible reactions with high controllabilities. The transient response of a given metabolite is most sensitive to reactions involving metabolites which are changing most rapidly relative to their respective pool sizes. Rapidly reversible reactions are most important for communication between metabolite pools.     

Temperature-Mediated Interaction of Tetanus Toxin with Cerebral Neuron Cultures: Characterization of a Neuraminidase-Insensitive Toxin-Receptor Complex

Abstract: Energy-dependent internalization of ¹²⁵I-labeled tetanus toxin into cultured neural cells is shown to follow an energy-independent binding process. A three-step model, involving receptor-mediated binding followed by sequestration and internalization is proposed. In the first step, binding of toxin is enhanced in appearance under low ionic strength medium, at 0–4°C; it is suppressed, however, with increasing incubation temperature under physiological salt concentrations. Cell-bound toxin is displaced by approximately 35.5% when high-salt medium (physiological concentrations) is added to cells at 0–4°C; the effect is further amplified at 37°C. Addition of disialoganglioside G_D1b (1–5 μg/ml) also lowers the amount of cell-associated toxin. The fraction of ¹²⁵I-labeled toxin retained by the cells after exposure to high-salt medium at 0–4°C or after addition of G_D1b is operationally defined as sequestered toxin. This second step, characterized by a stable association of the toxin with the neural cells, is affected by both physiological salt and by 37°C conditions. Lastly, an energy-dependent phenomenon of firm association of tetanus toxin with neural cells, compatible with internalization, is described. The toxin residing in this fraction is bioactive and cannot be removed by salts, gangliosides, or by treatment with protease or neuraminidase. Binding, sequestration, and internalization are mutually dependent, as they are all blocked by pretreatment of cells with neuraminidase and by an enhanced energy-independent sequestration event, which results in enhanced tetanus toxin internalization by an energy-dependent process.     

A graph-theoretical analysis of metabolic regulation

A graph theoretical method is proposed for modeling metabolic networks including enzymic cascades and synergistic binding of ligands to enzymes. Formal operations on the graph of a given network leads to the identification of feedback metabolites and the enzymes which regulate the feedback. These systemic properties are thus isolated from the purely local regulation of individual enzymes. The method was applied to a model of glycogen metabolism. At low cyclic AMP and insulin levels feedback control of the system is predicted to be largely with the glycogen branching and debranching enzymes, which set the amount of glycogen in the metabolically available outer branches.     

ERYTHROID CELL DIFFERENTIATION AND THE INHIBITION OF CYTOKINESIS BY CYTOCHALASIN

Cytochalasin B produces multinucleated erythroid cells in tissue cultures of very young chick blastoderms. There is no apparent qualitative interference with differentiation and maturation of erythroid cells, but the amounts produced are reduced 4- and 10-fold. These effects of cytochalasin are readily reversible.     

Transduction and Plasmid Deoxyribonucleic Acid Analysis in a Multiply Antibiotic-Resistant Strain of Staphylococcus epidermidis

A genetic analysis of a multiply antibiotic-resistant strain of Staphylococcus epidermidis was performed. Experiments designed to show reversion of organisms to antibiotic susceptibility, as well as studies of the influence of ultraviolet irradiation of phage on the transduction frequencies of the resistance markers, indicated that determinants of chloramphenicol (cml), tetracycline (tet), and neomycin (neo) resistance are present on separate plasmids, but the streptomycin marker is chromosomal. In 2 to 6% of tetracycline-resistant transductants, co-transduction of cml was also observed. By using CsCl-dye density gradients followed by neutral sucrose gradients, the plasmids carrying cml, tet, and neo could be isolated and their molecular weights could be determined. The tetracycline plasmid is shown to be incompatible with one of the cryptic plasmids of a recipient strain.     

Biochemical Localization of Alkaline Phosphatase in the Cell Wall of a Marine Pseudomonad

The various layers of the cell envelope of marine pseudomonad B-16 (ATCC 19855) have been separated from the cells and assayed directly for alkaline phosphatase activity under conditions established previously to be optimum for maintenance of the activity of the enzyme. Under conditions known to lead to the release of the contents of the periplasmic space from the cells, over 90% of the alkaline phosphatase was released into the medium. Neither the loosely bound outer layer nor the outer double-track layer (cell wall membrane) showed significant activity. A small amount of the alkaline phosphatase activity of the cells remained associated with the mureinoplasts when the outer layers of the cell wall were removed. Upon treatment of the mureinoplasts with lysozyme, some alkaline phosphatase was released into the medium and some remained with the protoplasts formed. Cells washed and suspended in 0.5 M NaCl were lysed by treatment with 2% toluene, and 95% of the alkaline phosphatase in the cells was released into the medium. Cells washed and suspended in complete salts solution (0.3 M NaCl, 0.05 M MgSO(4), and 0.01 M KCl) or 0.05 M MgSO(4) appeared intact after treatment with toluene but lost 50 and 10%, respectively, of their alkaline phosphatase. The results suggest that the presence of Mg(2+) in the cell wall is necessary to prevent disruption of the cells by toluene and may also be required to prevent the release of alkaline phosphatase by toluene when disruption of the cells by toluene does not take place.     

The role of adenosine 3′:5′-cyclic monophosphate in the division of WI 38 cells. The cellular response to prostaglandin E1 and the effects of an cyclic adenosine 3′:5′-cyclic monophosphate analogue and prostaglandin E1 on cell division

Inhibition of growth and DNA synthesis was observed in WI 38 cells incubated with 8-methylthioadenosine 3':5'-cyclic monophosphate or prostaglandin E(1). The effect of both compounds on cell growth was reversible. On removal of these compounds from culture media the cells initiated DNA synthesis and divided. In addition, prostaglandin E(1) stimulated cyclic AMP formation in these cells to over 40 times the normal basal value. The increase in cyclic AMP concentration in WI 38 cells after addition of prostaglandin E(1) showed a marked variation. Cells that had recently been treated with trypsin and plated at a lower cell density exhibited a smaller response to addition of prostaglandin E(1) than cells that had divided and reached confluence.