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S S Vogel

Publications and source records attributed to S S Vogel.

26 records · Page 2Linked to original sources
PubMed1992

Calcium-triggered fusion of exocytotic granules requires proteins in only one membrane.

We studied calcium-triggered fusion of sea urchin egg secretory granules to test whether membrane bound fusion proteins are required in both fusing membranes. Using both light scattering assays and video microscopy, we found that native granules fused to granules that had been inactivated with either trypsin or N-ethylmaleimide. Granules also fused with liposomes prepared from lipids extracted from egg cortices and with liposomes made from synthetic phospholipids and cholesterol. Granule-liposome fusion required no cytoplasmic proteins and was inhibited by N-ethylmaleimide. Thus, membrane fusion of exocytotic granules can be promoted by proteins residing on only one of the two membranes.

Animals↗
PubMed1992

Proteins on exocytic vesicles mediate calcium-triggered fusion.

In many exocytic systems, micromolar concentrations of intracellular Ca2+ trigger fusion. We find that aggregates of secretory granules isolated from sea urchin eggs fuse together when perfused with greater than or equal to 10 microM free Ca2+. Mixing of membrane components was demonstrated by transfer of fluorescent lipophilic dye, and melding of granule contents was seen with differential interference microscopy. A technique based upon light scattering was developed to conveniently detect fusion. Two protein modifiers, trypsin and N-ethylmaleimide, inhibit granule-granule fusion at concentrations similar to those that inhibit granule-plasma membrane fusion. We suggest that molecular machinery sufficient for Ca(2+)-triggered fusion resides on secretory granules as purified and that at least some of these essential components are proteinaceous.

Animals↗
PubMed1991

Pertussis toxin-sensitive G proteins are transported toward synaptic terminals by fast axonal transport.

We find that half of the pertussis toxin-sensitive guanine nucleotide-binding protein (G protein) in the squid (Loligo pealei) giant axon is cytoplasmic and that this species of G protein is intermediate in size between the two forms present in axolemma. This G protein is transported toward synaptic terminals at 44 mm/day. Moreover, these data are consistent with there being two additional steps leading to the maturation of G proteins: (i) association with and transport on intracellular organelles and (ii) modification at the time of transfer to the plasmalemma resulting in a molecular weight shift. Since the other two components of G protein-mediated signal transduction pathways, receptors and effector enzymes, are known to be delivered to the synaptic terminals by fast axonal transport, our findings introduce the possibility that these three macromolecules are assembled as a complex in the cell body and delivered together to the plasma membrane of the axon and synaptic terminals.

Adenosine Diphosphate Ribose↗
PubMed1990

Characterization of synaptophysin and G proteins in synaptic vesicles and plasma membrane of Aplysia californica.

Two components of synaptic terminals that may be involved in transmitter release are synaptophysin (p38) and G proteins. In order to study release mechanisms in Aplysia californica we have prepared subcellular fractions from nervous tissue to characterize and localize these components. We identify Aplysia synaptophysin by Western blot analysis with monoclonal antibody SY38, find that it is enriched in synaptic vesicles, and, using immunocytochemistry, show that it is localized to neuropil. These characteristics indicate that Aplysia synaptophysin is closely related to mammalian synaptophysin; it appears to be much smaller, however, having a mass of 28 kDa instead of 38 kDa. We previously determined that G protein subunits in Aplysia are enriched in neuropil and synaptosomes. We now show that within the synaptic terminal the pertussis toxin-sensitive alpha-subunit as well as the beta-subunit are associated with plasma membrane using [32P]ADP-ribosylation and Western blotting with G protein-specific antibodies.

Animals↗
PubMed1989

G proteins in Aplysia: biochemical characterization and regional and subcellular distribution.

We studied G proteins and regulation of adenylate cyclase in nervous tissue and muscle of Aplysia using bacterial toxin-catalyzed ADP-ribosylation. We identified Gs alpha, a Mr 45,000 cholera toxin substrate, Go alpha, a Mr 40,000 pertussis toxin substrate, and G beta (Mr 37,000) by Western blot analysis with antisera specific for bovine brain G protein subunits. Partial proteolysis suggests that the neuronal pertussis toxin substrates are heterogeneous. The concentration of these substrates in membranes from Aplysia ganglia is similar to that of rat, squid and Helix; in Aplysia nervous tissue, G protein subunits are most enriched in synaptosomes and neuropil. The stimulation of adenylate cyclase by serotonin (5-HT), low concentrations of GTP-gamma-S, and cholera toxin, and the inhibition by high concentrations of GTP-gamma-S that is blocked by pertussis toxin indicate that both a Gs and a Gi protein regulate the Aplysia enzyme. These results support the idea that G proteins in Aplysia are important in regulating synaptic function.

Adenosine Diphosphate↗
PubMed1989

Aplysia synaptosomes. I. Preparation and biochemical and morphological characterization of subcellular membrane fractions.

We prepared and characterized subcellular membrane fractions from the CNS of Aplysia californica that are enriched in isolated nerve terminals (synaptosomes). Ganglia were homogenized in 1.1 M sucrose and fractionated on a 2-step sucrose gradient, yielding 50 micrograms protein/animal in the synaptosomal fraction (P3), which was enriched 3-fold in plasma membrane as compared with the initial homogenate. Quantitative morphometry of electron micrographs revealed that P3 contained 25% intact synaptosomes, a 5-fold enrichment over the homogenate. Although fractionation on a 5-step sucrose gradient reduced the yield of protein in the synaptosomal fraction to 40 micrograms/animal, this fraction (the 0.35 M/0.75 M interface) was more enriched in plasma membrane than P3 and was less contaminated by lysosomes and free mitochondria. By electron microscopy, the 0.35 M/0.75 M interface contained up to 50% synaptosomes. Synaptosomal fractions contained cAMP-, Ca2+/calmodulin-, and Ca2+/phospholipid-dependent protein kinase activities and were enriched in a Mr 40,000 pertussis toxin substrate, Gi/o. In the accompanying paper, we show that these synaptosomes retain the ability to release transmitters.

Animals↗
PubMedDate not supplied

The stability of N-pyrrolidinomethyltetracycline in solutions.

In aqueous solution N-pyrrolidinomethyltetracycline (PTC) undergoes decomposition into tetracycline, epitetracylcine, anhydroepitetracycline and ynhydrotetracycline. The decomposition products were identified and separated by TLC and their activity was estimated microbiologically.

Chromatography, Thin Layer↗