The role of G-proteins in coupling cell surface receptors to phospholipase C: Studies in Xenopus oocytes.
Item
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Title
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The role of G-proteins in coupling cell surface receptors to phospholipase C: Studies in Xenopus oocytes.
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Identifier
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AAI9020789
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identifier
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9020789
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Creator
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Moriarty, Thomas Michael.
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Contributor
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Adviser: Emmanuel M. Landau
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Date
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1990
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Molecular | Biology, Neuroscience
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Abstract
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G-proteins are a family of guanine nucleotide-binding regulatory proteins that serve to transduce extracellular signals from cell surface receptors across the plasma membrane to intracellular effector systems. The G-proteins are cytoplasmic, membrane-associated heterotrimers composed of {dollar}\alpha{dollar}, {dollar}\beta{dollar} and {dollar}\gamma{dollar} subunits. Many G-proteins have been purified and cloned, but only two have undisputed functions: G{dollar}\sb{lcub}\rm s{rcub}{dollar} for activation of adenylyl cyclase and G{dollar}\sb{lcub}\rm t{rcub}{dollar} for activation of the retinal cGMP phosphodiesterase.;Phospholipase C is the effector enzyme of the inositol phospholipid second messenger system. It is found in all cell types and can be stimulated by a number of extracellular signals, including neurotransmitters, hormones and growth factors. Phospholipase C controls various cellular processes, including excitation, contraction, secretion, metabolism and cell growth and differentiation, through the bifurcating second messenger cascades, IP{dollar}\sb 3{dollar} and diacylglycerol. Recent evidence has implicated a role for G-proteins in coupling receptors to phospholipase C. The evidence also suggests there exists two independent pathways: one sensitive to pertussis toxin and one insensitive. The studies described in this thesis help to elucidate the role of G-proteins in stimulation of phospholipase C.;The receptor evoked IP{dollar}\sb3{dollar}-dependent Cl{dollar}\sp{lcub}-{rcub}{dollar} conductance of the Xenopus oocyte was used as a model system of the receptor regulated phospholipase C. Receptor stimulation was by either the native oocyte muscarinic receptor or by various receptors expressed in the oocyte after injection of exogenous mRNA. Using pertussis toxin and purified G-protein subunits, the muscarinic receptor stimulated phospholipase C was found to be dependent on a pertussis toxin-sensitive G-protein and to be activated by subunit dissociation mechanism proposed for the adenylyl cyclase system. Using purified G-protein heterotrimers and GTP{dollar}\gamma{dollar}S-activated {dollar}\alpha{dollar}-subunits, the 39 kD G-protein G{dollar}\sb{lcub}\rm o{rcub}{dollar} was found to be uniquely capable of serving as the signal transducer of the pertussis toxin-sensitive receptor stimulated phospholipase C. Studies with receptors from liver and brain expressed in the oocyte demonstrate the capability of some receptors to couple both the pertussis toxin-sensitive and toxin-insensitive pathways, whereas others do not have this ability to crosstalk. This also suggests that the primary structure of the G-protein serving the pertussis toxin insensitive pathway is probably quite similar to G{dollar}\sb{lcub}\rm o{rcub}{dollar}, possibly differing by only one amino acid.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
