The biological activity of glucagon–phospholipid complexes

1983 ◽  
Vol 61 (7) ◽  
pp. 688-691 ◽  
Author(s):  
J. J. Liepnieks ◽  
P. Stoskopf ◽  
E. A. Carrey ◽  
C. Prosser ◽  
R. M. Epand
Keyword(s):  
Biological Activity ◽  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Bovine Brain ◽  
Water Soluble ◽  
Dipalmitoyl Phosphatidylcholine ◽  
Dimyristoyl Phosphatidylcholine ◽  
Lipoprotein Complex ◽  
Stimulation Of

Glucagon can form water-soluble complexes with phospholipids. The incorporation of glucagon into these lipoprotein particles reduces the biological activity of the hormone. The effect is observed only at temperatures below the phase transition temperature of the phospholipid and results in a decreased stimulation of the adenylate cyclase of rat liver plasma membranes by the lipoprotein complex as compared with the hormone in free solution. Two- to five-fold higher concentrations of glucagon are required for half-maximal stimulation of adenylate cyclase when the hormone is complexed with dimyristoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine, or bovine brain sphingomyelin. A possible role of lipoprotein-associated hormones in the development of insulin resistance is discussed.

Role of plasma membranes in stimulation of RNA-directed DNA synthesis

Nature ◽  
1976 ◽  
Vol 262 (5571) ◽  
pp. 805-807 ◽  
Author(s):  
L. C. PADHY ◽  
S. K. KAR ◽  
K. K. RAO ◽  
M. R. DAS
Keyword(s):  
Dna Synthesis ◽  
Plasma Membranes ◽  
Stimulation Of

Stimulation of Brain Synaptosome - Associated Adenylate Cyclase by Acidic Phospholipids

1984 ◽  
Vol 39 (11-12) ◽  
pp. 1196-1198 ◽  
Author(s):  
Stylianos Tsakiris
Keyword(s):  
Enzyme Activity ◽  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Protein S ◽  
Enzyme Activation ◽  
Dog Brain ◽  
The Central Nervous System ◽  
Acidic Phospholipids ◽  
Synaptosomal Plasma Membranes ◽  
Stimulation Of

Phosphatidylserine (PS), phosphatidylinositol (PIN) or phosphatidylglycerol (PGL) incubated with synaptosomal plasma membranes (SPM) of dog brain, stimulated adenylate cyclase. The enzyme activity showed a dramatic increase at around 1.6 μmol PS/mg protein, while use of higher concentrations led to inhibition of the activity with respect to the maximal percentage of stimulation. Moreover, PS stimulated the dopamine-sensitive adenylate cyclase. Solubilization of SPM by the detergent Lubrol-PX did not affect the enzyme activation induced by dopamine. The solubilization, also, showed that the enzyme activity does not change at any PS, PIN or PGL concentration used. These results indicate that acidic phospholipids do not directly act on adenylate cyclase, but indirectly, affecting the membrane fluidity probably. Such modifications of interactions through lipid-protein(s) of adenylate cyclase may have implications to physiological responses to hormones or/and neurotransm itters in the central nervous system.

scholarly journals Role of prostaglandins in hypoxia-stimulated erythropoietin production

1985 ◽  
Vol 249 (1) ◽  
pp. C3-C8 ◽  
Author(s):  
A. Kurtz ◽  
W. Jelkmann ◽  
J. Pfeilschifter ◽  
C. Bauer
Keyword(s):  
Arachidonic Acid ◽  
Adenylate Cyclase ◽  
Cell Cultures ◽  
Mesangial Cells ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Cyclooxygenase Inhibitor ◽  
Erythropoietin Production ◽  
Stimulation Of

The role of prostaglandins in the mediation of hypoxia-stimulated erythropoietin (Ep) production by cultured rat renal mesangial cells was examined. It was found that an increase in prostaglandin E2 (PGE2) production accompanied the rise in Ep due to hypoxia (2% O2). The hypoxia-stimulated increase in Ep production was abolished in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M). When PGE2 (10(-6) M was added simultaneously with indomethacin, however, no diminution in hypoxia-stimulated Ep production was observed. Addition of arachidonic acid (AA, 10(-5) M), PGE2 (10(-6) M), or PGI2 (10(-4) M) enhanced Ep production under normoxic conditions (20% O2), while PGF2 alpha (10(-6) M) had no effect on Ep production. AA, PGE2, and PGI2 were found to stimulate adenosine 3',5'-cyclic monophosphate formation by the cultured mesangial cells. Enhancement of adenylate cyclase activity by forskolin (10(-5) M) also increased Ep production in the cell cultures. Our results suggest that hypoxia-stimulated Ep production by cultured mesangial cells is mediated by prostaglandins with subsequent stimulation of adenylate cyclase activity.

scholarly journals The role of GTP in prostaglandin E1 stimulation of adenylate cyclase in platelet membranes

1983 ◽  
Vol 214 (1) ◽  
pp. 231-234 ◽  
Author(s):  
J M Stein ◽  
B R Martin
Keyword(s):  
Adenylate Cyclase ◽  
Prostaglandin E1 ◽  
Platelet Membrane ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Dependent Inhibition ◽  
Dose Dependent Inhibition ◽  
Dose Dependent ◽  
Stimulation Of

Adenylate cyclase activity in platelet membrane preparations was measured in the presence of prostaglandin E1 (PGE1), GTP and a non-hydrolysable analogue of GDP, guanosine 5′-[beta-thio]diphosphate (GDP[beta S]). A dose-dependent inhibition of adenylate cyclase by GDP[beta S] was observed that could be reversed either by adding increased amounts of GTP or of PGE1.

scholarly journals G-protein inhibition of phospholipase C-β1 in membranes: role of G-protein βγ subunits

1996 ◽  
Vol 319 (1) ◽  
pp. 173-178 ◽  
Author(s):  
Irene LITOSCH
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Plasma Membranes ◽  
Bovine Brain ◽  
Protein Inhibition ◽  
Low Concentrations ◽  
Dependent Inhibition ◽  
Cortical Membranes

Rat liver plasma membranes reconstituted with bovine brain phospholipase C β1 (PLC-β1) exhibit a dual regulation of PLC-β1 activity by G-proteins. Guanosine 5´-[γ-thio]triphosphate (GTP[S]; 0.1 nM) produced a 20-25% inhibition of PLC-β1 activity within 7 min of incubation. The addition of vasopressin resulted in near-basal levels of activity in the presence of 0.1 nM GTP[S]. Clonidine had little effect on the net inhibition due to GTP[S]. A similar antagonism between carbachol and GTP[S] occurred in cerebral cortical membranes containing endogenous PLC-β1 activity. αo/i-GDP (a mixture of GDP-liganded Goα and Giα) attenuated the GTP[S]-dependent inhibition of PLC-β1 whereas αo/i-GTP[S] had no effect, suggesting an involvement of G-protein βγ subunits in the inhibition of PLC-β1. Low concentrations of βγ subunits inhibited PLC-β1 activity. Inhibition was followed by reversal to basal activity and onset of stimulation as the βγ concentration was increased. Inhibition by βγ was dependent on the presence of membranes. These results indicate that G-protein βγ subunits constitute a mechanism by which G-proteins mediate a rapid and transient inhibition of PLC-β1.

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