scholarly journals Zymosan-induced release of inositol phosphates at resting cytosolic Ca2+ concentrations in macrophages

1987 ◽  
Vol 242 (2) ◽  
pp. 441-445 ◽  
Author(s):  
J Moscat ◽  
C Herrero ◽  
P Garcia-Barreno ◽  
A M Municio
Keyword(s):  
Phospholipase C ◽  
Inositol Phosphates ◽  
Binding Protein ◽  
Nucleotide Binding ◽  
Guanine Nucleotide ◽  
Guanine Nucleotide Binding Protein ◽  
Guanine Nucleotide Binding ◽  
The Relationship ◽  
Hydrolysis Of ◽  
Stimulation Of

Hydrolysis of polyphosphoinositides by phosphodiesterase has been demonstrated to be involved in the control of cytosolic Ca2+ concentrations. The stimulation of Ca2+ ionophores of the release of inositol phosphates in macrophages, and other cells, together with the Ca2+ requirements for zymosan-induced phospholipase C activation, make unclear the relationship between Ca2+ mobilization and polyphosphoinositide hydrolysis. The results in the present paper strongly suggest that, for zymosan-induced phospholipase C activation, a previous increase in cytosolic Ca2+ is not a required event. These results also show that zymosan-activated release of inositol phosphates may be mediated by a guanine-nucleotide-binding protein.

Stimulation of phospholipase C by guanine-nucleotide-binding protein betagamma subunits

1992 ◽  
Vol 206 (3) ◽  
pp. 821-831 ◽  
Author(s):  
Montserrat CAMPS ◽  
Cuifen HOU ◽  
Dimitrios SIDIROPOULOS ◽  
Jeffry B. STOCK ◽  
Karl H. JAKOBS ◽  
...  
Keyword(s):  
Phospholipase C ◽  
Binding Protein ◽  
Nucleotide Binding ◽  
Guanine Nucleotide ◽  
Guanine Nucleotide Binding Protein ◽  
Betagamma Subunits ◽  
Guanine Nucleotide Binding ◽  
Stimulation Of ◽  
Nucleotide Binding Protein

scholarly journals Phospholipase C-mediated hydrolysis of phosphatidylcholine is activated by muscarinic agonists

1989 ◽  
Vol 263 (1) ◽  
pp. 115-120 ◽  
Author(s):  
M T Diaz-Meco ◽  
P Larrodera ◽  
M Lopez-Barahona ◽  
M E Cornet ◽  
P G Barreno ◽  
...  
Keyword(s):  
Growth Factors ◽  
Phospholipase C ◽  
Guanine Nucleotide ◽  
Muscarinic Agonists ◽  
Guanine Nucleotide Binding Protein ◽  
Permeabilized Cells ◽  
Guanine Nucleotide Binding ◽  
Oncogene Products ◽  
Hydrolysis Of ◽  
Stimulation Of

The phospholipase C-catalysed breakdown of inositol-containing phospholipids is an important source of diacylglycerol in cells stimulated by several agonists. However, recent experimental evidence suggests that major phospholipids such as phosphatidylcholine may also be substrates of the phosphodiesteratic hydrolysis activated by hormones, growth factors and oncogene products. We show here that stimulation of muscarinic agonists activates the release of phosphocholine, which, along with diacylglycerol, is a metabolic product of phospholipase C-mediated hydrolysis of phosphatidylcholine. Fluoroaluminates mimic this muscarinic effect, strongly suggesting that carbachol-activated release of phosphocholine may be mediated by a guanine-nucleotide-binding protein. Evidence for this was obtained from experiments using permeabilized cells in which non-hydrolysable analogues of GTP activated phosphocholine release synergistically with carbachol.

scholarly journals Evidence for two GTPases activated by thrombin in membranes of human platelets

1986 ◽  
Vol 237 (3) ◽  
pp. 669-674 ◽  
Author(s):  
R Grandt ◽  
K Aktories ◽  
K H Jakobs
Keyword(s):  
Adenylate Cyclase ◽  
Binding Protein ◽  
Nucleotide Binding ◽  
Guanine Nucleotide ◽  
Guanine Nucleotide Binding Protein ◽  
Gtp Hydrolysis ◽  
Platelet Membranes ◽  
Guanine Nucleotide Binding ◽  
Stimulation Of ◽  
Nucleotide Binding Protein

Thrombin inhibits adenylate cyclase and stimulates GTP hydrolysis by high-affinity GTPase(s) in membranes of human platelets at almost identical concentrations. Both of these thrombin actions are similar to those observed with agonist-activated alpha 2-adrenoceptors coupling to the inhibitory guanine nucleotide-binding protein N1. However, stimulation of GTP hydrolysis caused by adrenaline (alpha 2-adrenoceptor agonist) and by thrombin at maximally effective concentrations was partially additive, whereas with regard to adenylate cyclase inhibition no additive response was observed. Furthermore, treatment of platelet membranes with pertussis toxin, which inactivates Ni and largely abolishes thrombin- and adrenaline-induced adenylate cyclase inhibition and adrenaline-induced GTPase stimulation, decreased the thrombin-induced stimulation of GTP hydrolysis by only about 30%. Additionally, the thiol reagent N-ethylmalemide (NEM) at rather low concentrations abolished thrombin- and adrenaline-induced stimulation of GTP hydrolysis was decreased by only 30-40% by treatment of platelet membranes with even high concentrations of NEM. Treatment with cholera toxin, which inhibits GTPase activity of the Ns (stimulatory guanine nucleotide-binding) protein, has no effect on thrombin-stimulated GTP hydrolysis. The data suggest that thrombin interaction with its receptor sites in platelet membranes leads to stimulation of two GTP-hydrolysing enzymes. One of these enzymes is apparently Ni and is also activated by agonist-activated alpha 2-adrenoceptors and is inactivated by pertussis toxin and NEM treatment. The other GTP-hydrolysing enzyme activated by thrombin may represent a guanine nucleotide-binding protein apparently involved in the coupling of thrombin receptors to the phosphoinositide phosphodiesterase.

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