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Biomedical subjects

S Spiegel

Publications and source records attributed to S Spiegel.

155 records · Page 9Linked to original sources
PubMed1983

Grafting of triggering site onto lymphocytes; distribution of grafted dinitrophenyl groups on cell surface glycoproteins and glycolipids.

Quantitative investigation of membrane-bound sialoglycoconjugates on lymphocyte surface was performed by chemical modification of the sialic acid residues with radioactive N4-dinitrophenyl-L-2,4-diaminobutyric acid hydrazide (DNP-DABH). This labeled both glycoproteins and glycolipids with concomitant preservation of the mitogenic activity by multivalent hapten binding protein (anti-DNP antibody). Under conditions where maximum stimulation of thymocytes occurred radioactive DNP-DABH labeled 1.1 X 10(7) glycolipids molecules/cell but, only 3 X 10(6) glycoproteins molecules/cell. When B lymphocytes, which do not undergo DNP-mediated stimulation were used, glycolipids labeling could not be detected. Major differences between stimulation committed and non-committed DNP-modified lymphocytes was the amount of ligand attached to the cell surface sialoglycolipids (gangliosides).

Animals↗
PubMed1982

A novel approach for the topographical localization of glycolipids on the cell surface.

In this study we have developed a prototype system for distinguishing between the topographical distribution of glycolipids versus glycoproteins on the ultrastructural level. Direct modification of membrane-based sialic acids with biotin groups labels both glycolipids and glycoproteins. In this case, subsequent ultrastructural localization of biotinylated sites would not discern between these two classes of glycoconjugate in an unambiguous manner. When biotinylated cells are fixed prior to interaction with ferritin-conjugated avidin, the mean distance of marker molecules from the membrane bilayer is 8.0 nm. In contrast, if the cells are allowed to cap through the action of ferritin-avidin conjugates on unfixed cells, the average distance (13.0 nm) of the marker molecules appears even more distant from the membrane on the capped portion of the cell (uropod), whereas those on the head region are positioned in close proximity to the bilayer (3.7 nm). In order to exclusively label cell surface glycolipids on the ultrastructural level, bovine brain gangliosides were biotinylated in vitro and the haptenized gangliosides were incorporated into intact cells. In this case, marker molecules denoting the incorporated gangliosides were found in relatively close juxtaposition to the membrane surface, in a manner strikingly similar to the labeling pattern of the head region on capped cells. These results support the concept that, in the native state, the carbohydrate portion of glycolipids is positioned closer to the membrane bilayer than that of glycoproteins.

Animals↗
PubMed1981

Membrane sialoglycolipids emerging as possible signal transducers for lymphocyte stimulation.

Biotin hydrazide was attached covalently to the aldehyde groups produced by periodate oxidation of bovine brain gangliosides. These modified gangliosides were incorporated into mature rat thymocytes by incubation of the biotinyl gangliosides in the culture medium containing these cells. Avidin, which binds strongly to biotin, agglutinated and stimulated DNA synthesis in thymocytes containing the incorporated biotin-tagged gangliosides. Avidin has no mitogenic effect on normal thymocytes or on cells that incorporate unmodified gangliosides. With fluoresceinated avidin, the incorporated biotinyl gangliosides are shown to be laterally redistributed into patches and caps. These results imply that gangliosides may be involved in transmembrane communication during lymphocyte stimulation.

Animals↗
PubMed1979

A computer program for simulating a distributed metabolic system. Distribution volumes in a simulated organism.

A metabolite or hormone is distributed with non-uniform concentration throughout some volume within an intact organism. Various methods involving radioactive tracers are used to estimate the total mass of the metabolite and its volume of distribution. The calculations of mass and volume are based on very simple models, and cannot usually be validated by measurements on the real animal. Hence we have developed a computer program for simulating a metabolic system with convective and diffusive transport. The tracer experiments can be simulated by solving the differential equations for convective diffusion by finite element methods. Thus the total metabolic mass and distribution volume can be both 'measured' and calculated by all the standard techniques. In this way some mathematical methods currently in general use can be seen to be patently incorrect, and others quite acceptable. The concept of a metabolic doublet was introduced, by analogy with an electrical dipole.

Biological Transport↗
PubMed1979

Involvement of gangliosides in lymphocyte stimulation.

N4-Dinitrophenyl-L-2,4-diaminobutyric acid hydrazide was attached covalently to the aldehyde groups produced by periodate oxidate of bovine brain gangliosides and it was incorporated into mature thymocytes. High concentrations of antibodies to dinitrophenyl (DNP) or lower concentrations followed by protein A agglutinated the cells and stimulated DNA synthesis. Incubation of the thymocytes containing DNP-modified ganglioside with rabbit anti-DNP and fluorescein-labeled anti-rabbit IgG resulted in the formation of uniform rings on the cell surface, which subsequently developed into patches and caps. These results indicate that gangliosides may play a primary role in the lymphocyte activation process.

Agglutination↗
PubMed1975

Preformed mRNA and the programming of early embryo development.

A significant feature of the early development of fertilized echinoderm and amphibian eggs and germinating seed embryos is the utilization of genetic information that has been previously transcribed during oogenesis and seed ripening. When RNA synthesis is suppressed in the early developing embryos by actinomycin D, cordycepin, or alpha-amanitin, there is no effect on the translation of the "preformed mRNA", only a limited number have been thus far identified; microtubule and histone proteins in the fertilized sea urchin egg and carboxypeptidase and isocritric lyase in germinating cottonseed. Data obtained on the protein synthetic pattern at different times after the onset of development suggest that preformed mRNAs are made available to the translational system in a gradual process, thereby providing a molecular basis for the regulation of development. The possibility is considered that polyadenylation of mRNA, a reaction known to occur early after sea urchin fertilization, is responsible for regulating the release of preformed mRNA. It is shown that this reaction (polyadenylation) can be completely suppressed with little effect on the function of preformed mRNA. Finally, it is suggested, at least for the seed embryo system, that the formation of ATP may be a prerequisite for the activation of protein synthesis.

Amanitins↗
PubMed1975

Transcription of Ribosomal and Messenger RNAs in Early Wheat Embryo Germination.

Germinating wheat embryos (Triticum aestivum L). synthesize both ribosomal and messenger RNA at the earliest times after the onset of germination. The rates of synthesis of these two RNAs are determined at various stages in germination by an analysis of newly synthesized radioactive RNA on oligo(dT)-cellulose. The rate of messenger RNA synthesis is essentially constant throughout 18 hours of germination, while that of ribosomal RNA synthesis increases steadily, particularly after the onset of cell expansion (6 hours), reaching at 16 to 18 hours, a rate of synthesis between 5- and 20-fold greater than that observed at the earliest stages. The net effect is a relative decrease in the fraction of transcribed high molecular weight RNA that is mRNA. Throughout the first 7 hours of germination, mRNA is 25 to 30% of the transcribed fraction, whereas by 16 to 18 hours it has declined to a level of 4 to 8%.

Journal Article↗
PubMedDate not supplied

Interaction of quaternary ammonium and phosphonium salts with photosynthetic membranes.

Distinct concentration ranges of selected quaternary ammonium and phosphonium salts were elaborated to induce stimulatory or inhibitory effects, respectively, on photosynthetic reactions. By means of fluorescence induction measurements 3 different effects of alkylbenzyldimethylammonium chloride (ABDAC; zephirol) in chloroplast preparations from Pisum sativum were observed. 60 microM ABDAC produced a strong increase in Fmax with concurrently improved Kautsky kinetics. Increased ABDAC concentration (500 microM) led to a strong fluorescence quenching - virtually indistinguishable from the conditions following the addition of photosystem II electron acceptors like K3Fe[CN]6. Further increase of ABDAC to 5 mM provoked a drastic increase in the fluorescence yield together with the complete loss of any detectable kinetics. We suggest a 3-step interaction of ABDAC with the thylakoid membranes of photosynthetic organisms similar to our earlier discussion (Bader and Höper (1993), Z. Naturforsch. 49c, 87-94). We examined a series of derivatives with selectively modified side chains, central atoms and counter ions, respectively. Both an alkyl chain of the type ([-CH2-]n; n approximately > 10) and effective polar components are indispensable for the adsorption and intercalation of the molecule onto and into the thylakoid membranes. The benzyl group could be replaced by a methyl residue without any loss of effectiveness; replacement of the central nitrogen (N) by phosphorus (P) and the counter ion Cl by Br did not modify the effects and the results were indistinguishable from the ABDAC effect proper. Shortening of the alkyl chain to (-CH2-)6 resulted in a less effective interaction of e.g. tetraoctylammonium bromide with the photosynthetic membrane. Flash-induced oxygen evolution measurements with selected derivatives (15 microm) substantiated our interpretation of an improved OEC functioning by a substantial lowering of the miss parameter a and the exclusion of a chemical reduction as the standard S-state distribution was not affected. As evidenced by both SDS-PAGE and Western blot analyses the investigated molecules showed a direct interaction. The polypeptide patterns were characterized by a severe shift of the molecular weight components from high (20-67 kDa) to low (< 20 kDa) values.

Kinetics↗