Collagen receptors mediate early events in the attachment of epithelial (MDCK) cells

Summary Madin-Darby canine kidney (MDCK) cells kept in suspension culture for 12–15 hr displayed high-affinity binding sites for¹²⁵I-lathyritic (soluble) collagen (120,000/cell,K _D =30nm) and preferred collagens types I and IV over laminin or fibronectin as substrates during the first hour of attachment. On the other hand, after 4 hr, attachment to all four substrates was equally efficient. Upon challenge with a collagen substrate, the high-affinity sites were rapidly recruited on it (T1/2=6 min). Their occupancy by soluble collagen triggered the exocytosis of a second large population of low-affinity collagen binding sites that included laminin and seems to be involved in a second cell-attachment mechanism. These results are compatible with a twostep model of MDCK cell attachment to the substrate: first, via high-affinity collagen binding sites, and second, via laminin of cellular origin.     

Activation of pigeon erythrocyte adenylate cyclase by cholera toxin partial purification of an essential macromolecular factor from horse erythrocyte cytosol

A cytosolic, macromolecular factor required for the cholera toxin-dependent activation of pigeon erythrocyte adenylate cyclase and cholera toxin-dependent ADP-ribosylation of a membrane-bound 43 000 dalton polypeptide has been purified 1100-fold from horse erythrocyte cytosol using organic solvent precipitation and heat treatment. This factor, 13 000 daltons, does not absorb to anionic or cationic exchange resins, is sensitive to trypsin or 10% trichloroacetic acid and is not extractable by diethyl ether. Activation of adenylate cyclase by cholera toxin requires the simultaneous presence of ATP (including possible trace GTP), NAD⁺, dithiothreitol, cholera toxin, membranes and the cytosolic macromolecular factor. Reversal of cholera toxin activation of adenylate cyclase, and of the toxin-dependent ADP-ribosylation, requires the presence of the cytosolic factor. The ability of the purified cytosolic factor to influence the hormonal sensitivity of liver membrane adenylate cyclase may provide clues to its physiological functions.     

Demonstration of choleragen-dependent ADP-ribosylation in whole cells and correlation with the activation of adenylate cyclase

3T3C₂ mouse fibroblasts rendered permeable to (α^?32P)NAD⁺ show cholera toxin-dependent labeling of a 45,000 m.w. protein and of a doublet of polypeptides around 52,000 m.w. These same bands are ADP-ribosylated in broken cells. Membranes prepared from pigeon erythrocytes pretreated with choleragen show a decrease in subsequent cholera toxin-specific ADP-ribosylation of a 43,000 m.w. polypeptide. Both whole cell and broken cell adenylate cyclase activation and toxin-specific ADP-ribosylation are reversed specifically by low pH and high concentrations of toxin and nicotinamide in all systems. Thus ADP-ribosylation appears to be relevant to the molecular action of choleragen in whole cells as well as in broken cells.     

The Ultrastructure of the Gastrodermal Gland Cells in the Freshwater Planarian Dugesia gonocephala s.l.

Light and transmission electron microscopy have been used to study the gastrodermal gland cells of the triclad Dugesia gonocephala s.l. The events involved in the ultrastructural transformation and the secretion process in these cells were followed at four different stages in both fasted and fed animals. During the feeding stage their secretory granules are directly discharged into the intestinal lumen by means of a secretion process of the holocrine type that is described in this paper. It is suggested that such secretions contribute to extracellular digestion and that disintegration of the gland cells is accompanied by a differentiation of neoblasts into new gland cells, reflecting a turnover of gland cells during the triclad digestive stages.     

Peptidoglycan tripeptide content and cross-linking are altered in Enterobacter cloacae induced to produce AmpC beta-lactamase by glycine and D-amino acids.

Induction of AmpC beta-lactamase in Enterobacter cloacae ATCC 13047 by D-methionine, glycine, or D-tryptophan was accompanied by alterations in peptidoglycan composition and structure; in the case of D-methionine, it was also accompanied by morphologic changes. A decrease in peptidoglycan tripeptides was seen. With glycine, there was an increase in the proportion of diaminopimelic-diaminopimelic cross-links. The possible implications of these changes for beta-lactamase induction are discussed.     

BLOEM: A spatially explicit model of bioenergy and carbon capture and storage,applied to Brazil

Bioenergy could play a major role in decarbonizing energy systems in the context of the Paris Agreement. Large-scale bioenergy deployment could be related to sustainability issues and requires major infrastructure investments. It, therefore, needs to be studied carefully. The Bioenergy and Land Optimization Spatially Explicit Model (BLOEM) presented here allows for assessing different bioenergy pathways while encompassing various dimensions that influence their optimal deployment. In this study, BLOEM was applied to the Brazilian context by coupling it with the Brazilian Land Use and Energy Systems (BLUES) model. This allowed investigating the most cost-effective ways of attending future bioenergy supply projections and studying the role of recovered degraded pasture lands in improving land availability in a sustainable and competitive manner. The results show optimizing for limiting deforestation and minimizing logistics costs results in different outcomes. It also indicates that recovering degraded pasture lands is attractive from both logistics and climate perspectives. The systemic approach of BLOEM provides spatial results, highlighting the trade-offs between crop allocation, land use and the logistics dynamics between production, conversion, and demand, providing valuable insights for regional and national climate policy design. This makes it a useful tool for mapping sustainable bioenergy value chain pathways.     

Quantitative aspects of hormone-receptor interactions of high affinity: Effect of receptor concentration and measurement of dissociation constants of labeled and unlabeled hormones

It is demonstrated that because of limitations in the magnitude of the specific activity of radiolabeled hormone derivatives, direct binding studies of hormone-receptor interactions of high affinity (10^?9–10^?11 M, depending on whether ³H- or ¹²³I-labeled hormones are used) will be subject to artifactual distortions due to the need to utilize high concentrations of the receptor. If the concentration of the receptor is not ten times lower than the true affinity constant, the apparent dissociation constant obtained from direct concentration binding curves will vary as a linear function of the receptor concentration. In addition, at high receptor concentrations saturability becomes difficult to demonstrate experimentally and the binding data yield apparently non-hyperbolic, sigmoidal curves which can be mistakenly interpreted to depict cooperative interactions. Similar artifacts related to receptor concentration are predicted for measurements of the hormone concentration dependence of biological processes (e.g. activation of adenylate cyclase, transport processes, etc.). Methods for detecting these effects, and correctly measuring affinities for labeled and unlabeled hormones under these conditions, are described. The implications for measuring the binding properties of hormone-receptor interactions are discussed, especially in reference to studies of the comparative analysis of receptor function in altered metabolic states and to studies relating the biological and binding properties of hormones.