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Biomedical subjects

C Klein

Publications and source records attributed to C Klein.

At least 415 records · Page 23Linked to original sources
PubMed1977

Calcium ion effects on cyclic adenosine 3':5'-monophosphate bindings to the plasma membrane of Dictyostelium discoideum.

The study of cell surface cyclic adenosine 3':5'-monophosphate binding to Dictyostelium discoideum amoebae indicates that Ca2+ increases the number of binding sites without significantly affecting their affinity constant(s). The effects of the ion are observed immediately (within 4 s after addition) and appear to be readily reversible. Ca2+ effects are observed at various temperatures and pH values and are not blocked by the presence of various metabolic inhibitors. Increases, and decreases, in the apparent number of cyclic nucleotide binding sites could also be effected by concanavalin A treatments which respectively stimulate, and inhibit cell differentiation.

Calcium↗
PubMed1977

Principal cell types in the pancreatic islet of a teleost fish, Xiphorphorus helleri H.

By means of correlative light and electron microscopy, five pancreatic islet cell categories are described in the teleost fish, Xiphophorus helleri, each of which has specific light microscopic appearance and fine structure. Different histochemical techniques have been used, including immunofluorescence with antiporcine insulin and glucagon sera. In addition to B- and A1-cells, two categories of A2-cells have been observed both reacting with antiporcine glucagon serum: A2-cells with round granules gave a positive reaction for tryptophan; have been observed, both reacting with antiporcine glucagon serum: A2-cells with crystalline granules gave a negative reaction with the same staining technique on the same section. The "clear cells", the last category, were not specifically stained by any of the staining methods carried out in this investigation. The influence of fixation on staining affinities and on ultrastructure was shown to be considerable.

Animals↗
PubMed1977

cAMP,-induced changes in cAMP-binding sites on D; discoideum amebae.

Cell surface levels of 3H-cAMP binding to Dictyostelium discoideum amebae are dramatically reduced when cells are preincubated with cAMP. This decrease in 3H-cAMP binding is shown to reflect a loss in the number of binding sites and not in any significant change in their affinity constants(s). cAMP-mediated loss of its binding sites requires the continued presence of the cyclic nucleotide and does not depend upon protein synthesis. Reapparition of sites, which occurs when cAMP is eliminated from the media, also does not depend upon protein synthesis. Experiments using metabolic inhibitors and heat-killed cells suggest that the loss of binding sites is a direct consequence of the formation of cAMP-binding protein complexes.

Azides↗
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↗
PubMed1976

Physical and functional heterogeneity in TYMV RNA: evidence for the existence of an independent messenger coding for coat protein.

Turnip yellow mosaic virus RNA can be separated into two distinct components of 2 times 10(6) and 300 000 daltons molecular weight after moderate heat treatment in the presence of SDS or EDTA. The two species cannot have arisen by accidental in vitro degradation of a larger RNA, as they both possess capped 5' ends. Analysis of the newly synthesized proteins resulting from translation of each RNA by a wheat germ extract shows that the 300 000 molecular weight RNA can be translated very efficiently into coat protein. When translated in vitro the longer RNA gave a series of high molecular weight polypeptides but only very small amounts of a polypeptide having about the same mass as the coat protein. Thus our results suggest that the small RNA is the functional messenger for coat protein synthesis in infected cells.

Genetic Code↗
PubMed1975

Induction of phosphodiesterase by cyclic adenosine 3':5'-monophosphate in differentiating Dictyostelium discoideum amoebae.

Cyclic adenosine 3':5'-monophosphate added to the starvation media of Dictyostelium discoideum amoebae induces both intracellular and extracellular phosphodiesterase activities of these cells. The induced enzyme activity appears several hours earlier than that in starved cells which have not been induced with cyclic nucleotide. In both cases, the appearance of enzyme is inhibited by cycloheximide, and actinomycin D, and daunomycin. The KmS for the extracellular enzyme(s) of nucleotide-induced and uninduced control cells are identical. The induction of enzyme activity seems specific for cyclic adenosine 3':5'-monophosphate since cyclic guanosine 3':5'-monophosphate, as well as other nucleotides, have no effect. No differences in the activity or excretion of either N-acetylglucosaminidase or the inhibitory of the extracellular phosphodiesterase are observed between cyclic adenosine 3':5'-monophosphate-induced and control cells. A direct activation of phosphodiesterase by cyclic adenosine 3':5'-monophosphate can be excluded, since the addition of this nucleotide to cell lysates has no effect on the enzyme activity.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Immunohistological demonstration of insulin and glucagon in islet tissue of reptiles, amphibians and teleosts using epoxy-embedded material and antiporcine hormone sera.

Islet tissue from 2 reptilian, 5 amphibian and 7 teleost species was fixed in glutaraldehyde, embedded in epoxy-resin, stored for up to 3 years, cut in ultrathin sections and stained with the indirect immunofluorescent technique for insulin and glucagon following removal of the plastic. The antisera were directed against porcine insulin and glucagon, or FITC labeled and directed against the globulin fraction of the producer species. Positive results were obtained in species from all vertebrate classes investigated. Insulin demonstration in teleosts was particularly difficult.

Amphibians↗