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M Darmon

Publications and source records attributed to M Darmon.

87 records · Page 5Linked to original sources
PubMed1978

The role of phosphodiesterase in aggregation of Dictyostelium discoideum.

The role of cAMP phosphodiesterase in the cAMP-mediated aggregation of the cellular slime mould Dictyostelium discoideum was investigated with a morphogenetic mutant defective in phosphodiesterase production. Mutant cells become capable of aggregating normally when incubated in the presence of exogenous phosphodiesterase isolated from Idictyostelium or rat brain. Direct contact between enzyme and the cell membrane is not required for this phenotypic suppression. The aggregateless character of this strain presumably results from an over-accumulation of cAMP in the extracellular medium since aggregation can be induced in the absence of added phosphodiesterase under conditions facilitating diffusion of the nucleotide. This suggests that phosphodiesterase is not involved in the generation or recognition of cAMP signals, but that the enzyme is essential in the control of the cAMP signal-to-noise ratio.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

[Growth of "Dictyostelium discoideum" on different species of bacteria (author's transl)].

Dictyostelium discoideum (Acrasida) is a predatory amoeba feeding on bacteria of forest soil. Growth of D. discoideum on various bacterial species has been studied. The majority of the species of bacteria tested provide a convenient food source of D. discoideum. However, some species of bacteria do not permit growth of these amoebae; in some cases the reason of this unability has been established: it is due either to the incapacity for amoebae to phagoycte the bacteria or to the bacterial elaboration of compounds toxic for the amoebae.

Bacteria↗
PubMed1976

Binding of Concanavalin A and its effect on the differentiation of Dictyostelium Discoideum.

Dictyostelium discoideum amoebae have two classes of binding sites for concanavalin A, one accessible to a competitive inhibitor of concanavalin A binding and one inaccessible. Uptake of concanavalin A occurs and is associated with a transfer from accessible to inaccessible binding sites. Low amounts of concanavalin A bound to cells produce a slight stimulation of differentiation, and this is associated with an increase in production of phosphodiesterase. Above a critical amount of concanavalin A bound, cell differentiation and phosphodiesterase production are inhibited. The relationship of concanavalin A-induced membrane changes to cell differentation is discussed.

Acetylglucosaminidase↗
PubMed1976

A differentiation stimulating factor induces cell sensitivity to 3':5'-cyclic AMP pulses in dictyostelium discoideum.

During the first few hours of starvation, Dictyostelium discoideum amoebae excrete a macromolecule, probably a glycoprotein, which stimulates cell differentiation to aggregation competence. 3':5'-Cyclic AMP pulses, which mimic the chemotactic signal, and this factor (differentiation stimulating factor) are shown to exert a cooperative effect in inducing cell differentiation. Data suggest that the appearance of the factor determines the moment amoebae become responsive to cyclic AMP pulses.

Cell Aggregation↗
PubMed1975

Chemotactic signals induce cell differentiation in Dictyostelium discoideum.

Experiments carried out with the aid of cellophane membranes demonstrate that the morphogenetic block of certain nonaggregating, "aggregateless," mutants may be overcome by diffusible factors excreted by aggregating wild-type cells. The same differentiation process into aggregation-competent cell is observed if mutant amoebae are subjected to external 3':5'-cAMP pulses imposed at 5 min intervals. Wild-type amoebae also respond to cAMP pulses, since the onset of differentiation is more precocious in pulsed than in unpulsed populations. These data suggest that chemotactic signals act as an inducer of cell differentiation.

Adenosine Monophosphate↗
PubMedDate not supplied

Presence of serum albumin in normal human epidermis: possible implications for the nutrition and physiology of stratified epithelia. Presence of albumin in epidermis.

In this paper, using both immunofluorescence and protein biochemistry techniques, we present definitive evidence that plasma proteins such as albumin are present within normal human epidermis. This result confirms several previous reports supporting the idea that relatively large molecules can diffuse through the epidermal basement membrane into epidermis. Our results bring new insights for discussing how hydrophobic ligands or drugs present in the bloodstream and bound to plasmatic carriers can reach epidermal cells of all layers.

Electrophoresis, Gel, Two-Dimensional↗
PubMedDate not supplied

[A complementary phage-typing scheme for "P. aeruginosa" (author's transl)].

Twenty per cent of Pseudomonas aeruginosa strains isolated in Portugal are non typable with the phage-typing Lindberg system, but most of them may be typed with the aid of a new phage-typing method. This complementary scheme of phage-typing is based on the use of 15 new phages from sewage; 39 phage-types were found among a group of the non-typable strains isolated in several hospitals in Lisbonne. The relations between the serotypes, the pyocinotypes and the new lysotypes are investigated.

Bacteriophage Typing↗