scholarly journals Fluoroaluminates mimic guanosine 5′-[γ-thio]triphosphate in activating the polyphosphoinositide phosphodiesterase of hepatocyte membranes. Role for the guanine nucleotide regulatory protein Gp in signal transduction

1987 ◽  
Vol 241 (2) ◽  
pp. 409-414 ◽  
Author(s):  
S Cockcroft ◽  
J A Taylor
Keyword(s):  
Regulatory Protein ◽  
Active Species ◽  
Adenylate Cyclase System ◽  
Dependent Manner ◽  
Guanine Nucleotide ◽  
Concentration Dependent Manner ◽  
Phosphatidylinositol Bisphosphate ◽  
Species Analysis ◽  
Guanine Nucleotide Regulatory Protein ◽  
Gamma S

Fluoride and guanosine 5′-[gamma-thio]triphosphate (GTP gamma S) both activate the hepatocyte membrane polyphosphoinositide phosphodiesterase (PPI-pde) in a concentration-dependent manner. AlCl3 enhances the fluoride effect, supporting the concept that [A1F4]- is the active species. Analysis of the products of inositol lipid hydrolysis demonstrate that phosphatidylinositol bisphosphate is the major lipid to be hydrolysed. Guanosine 5′-[beta-thio]diphosphate (GDP beta S) is an inhibitor of activation of PPI-pde by both fluoride and GTP gamma S. These observations suggest that the guanine nucleotide regulatory protein (termed Gp) bears a structural resemblance to the well-characterized G-proteins of the adenylate cyclase system and the cyclic GMP phosphodiesterase system in phototransduction.

scholarly journals Guanine nucleotide-dependent pertussis-toxin-insensitive stimulation of inositol phosphate formation by carbachol in a membrane preparation from human astrocytoma cells

1986 ◽  
Vol 239 (1) ◽  
pp. 141-146 ◽  
Author(s):  
J R Hepler ◽  
T K Harden
Keyword(s):  
Pertussis Toxin ◽  
Inositol Phosphate ◽  
Regulatory Protein ◽  
Dependent Manner ◽  
Guanine Nucleotide ◽  
Astrocytoma Cells ◽  
Human Astrocytoma ◽  
Guanine Nucleotide Regulatory Protein ◽  
Human Astrocytoma Cells ◽  
Stimulation Of

The efficacy of muscarinic-receptor agonists for stimulation of inositol phosphate formation and Ca2+ mobilization in intact 1321N1 human astrocytoma cells is correlated with their capacity for formation of a GTP-sensitive high-affinity binding complex in membranes from these cells [Evans, Hepler, Masters, Brown & Harden (1985) Biochem. J. 232, 751-757]. These observations prompted the proposal that a guanine nucleotide regulatory protein serves to couple muscarinic receptors to the phospholipase C involved in phosphoinositide hydrolysis in 1321N1 cells. Inositol phosphate (InsP) formation was measured in a cell-free preparation from 1321N1 cells to provide direct support for this idea. The formation of InsP3, InsP2 and InsP1 was increased in a concentration-dependent manner (K0.5 approximately 5 microM) by guanosine 5′-[gamma-thio]triphosphate (GTP[S]) in washed membranes prepared from myo-[3H]inositol-prelabelled 1321N1 cells. Both GTP[S] and guanosine 5′-[beta gamma-imido]triphosphate (p[NH]ppG) stimulated InsP formation by 2-3-fold over control; GTP, GDP and GMP were much less efficacious. Millimolar concentrations of NaF also stimulated the formation of inositol phosphates in membrane preparations from 1321N1 cells. In the presence of 10 microM-GTP[S], the muscarinic cholinergic-receptor agonist carbachol stimulated (K0.5 approximately 10 microM) the formation of InsP above that achieved with GTP[S] alone. The effect of carbachol was completely blocked by atropine. The order of potency of nucleotides for stimulation of InsP formation in the presence of 500 microM-carbachol was GTP[S] greater than p[NH]ppG greater than GTP = GDP. Pertussis toxin, at concentrations that fully ADP-ribosylate and functionally inactivate Gi (the inhibitory guanine nucleotide regulatory protein), had no effect on InsP formation in the presence of GTP[S] or GTP[S] plus carbachol. These data are consistent with the idea that a guanine nucleotide regulatory protein that is not Gi is involved in receptor-mediated stimulation of InsP formation in 1321N1 human astrocytoma cells.

G-proteins, the inositol lipid signalling pathway, and secretion

1988 ◽  
Vol 320 (1199) ◽  
pp. 247-265 ◽  
Keyword(s):  
G Protein ◽  
Regulatory Protein ◽  
Pancreatic Acinar Cells ◽  
Secretory Process ◽  
Protein G ◽  
Guanine Nucleotide ◽  
Phosphatidylinositol Bisphosphate ◽  
Lipid Signalling ◽  
Intracellular Signals ◽  
Guanine Nucleotide Regulatory Protein

The formation of the second messenger cyclic AMP (cAMP) is known to be coupled to its receptor via a guanine nucleotide regulatory protein, G s . Ca 2+ -mobilizing receptors stimulate the hydrolysis of phosphatidylinositol bisphosphate (PtdIns(4,5) P 2 ), which generates two intracellular signals Ins(1,4,5) P 3 and diacylglycerol. We review the evidence that this signalling system is also composed of three types of proteins: receptor, G-protein and effector. The G-protein that couples to the effector, polyphosphoinositide phosphodiesterase (PPI-PDE), is a novel G-protein, G p , which is a substrate for pertussis toxin in some cells (e.g. neutrophils and platelets) but not others (e.g. pancreatic acinar cells and GH 3 cells). This implies that G p is not a single G-protein but encompasses a family of proteins that can activate PPI-PDE. We have also identified a role for another G-protein, G E , which is involved in the secretory process in mast cells and neutrophils. In this case, neither the receptor nor effector has been identified and the main evidence for proposing this second G-protein is based on the ability of guanine nucleotide analogues (e.g. GTPγS) to stimulate secretion independently of PPI-PDE activation.

Enhancement of hydroxyl radical generation by phenols and their reaction intermediates during ozonation

1998 ◽  
Vol 38 (6) ◽  
pp. 147-154 ◽  
Author(s):  
Hideo Utsumi ◽  
Sang-Kuk Han ◽  
Kazuhiro Ichikawa
Keyword(s):  
Hydroxyl Radical ◽  
Hydroxyl Radicals ◽  
Spin Trapping ◽  
Active Species ◽  
Generation Rate ◽  
Peak Height Ratio ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Phenol Derivatives ◽  
Semiquinone Radicals

Generation of hydroxyl radicals, one of the major active species in ozonation of water was directly observed with a spin-trapping/electron spin resonance (ESR) technique using 5,5-dimethyl-1-pyrrolineN-oxide (DMPO) as a spin-trapping reagent. Hydroxyl radical were trapped with DMPO as a stable radical, DMPO-OH. Eighty μM of ozone produced 1.08 X 10-6M of DMPO-OH, indicating that 1.4% of •OH is trapped with DMPO. Generation rate of DMPO-OH was determined by ESR/stopped-flow measurement. Phenol derivatives increased the amount and generation rate of DMPO-OH, indicating that phenol derivatives enhance •OH generation during ozonation of water. Ozonation of 2,3-, 2,5-, 2,6-dichlorophenol gave an ESR spectra of triplet lines whose peak height ratio were 1:2:1. ESR parameters of the triplet lines agreed with those of the corresponding dichloro-psemiquinone radical. Ozonation of 2,4,5- and 2,4,6-trichlorophenol gave the same spectra as those of 2,5- and 2,6-dichlorophenol, respectively, indicating that a chlorine group in p-position is substituted with a hydroxy group during ozonation. Amounts of the radical increased in an ozone-concentration dependent manner and were inhibited by addition of hydroxyl radical scavengers. These results suggest that p-semiquinone radicals are generated from the chlorophenols by hydroxyl radicals during ozonation. The p-semiquinone radicals were at least partly responsible for enhancements of DMPO-OH generation.

Sign in / Sign up

Export Citation Format

Share Document