title: Acidic phospholipid species inhibit adenylate cyclase activity in rat liver plasma membranes.
abstract: Incubation of rat liver plasma membranes with liposomes of dioleoyl phosphatidic acid (dioleoyl-PA) led to an inhibition of adenylate cyclase activity which was more pronounced when fluoride-stimulated activity was followed than when glucagon-stimulated activity was followed. If Mn2+ (5 mM) replaced low (5 mM) [Mg2+] in adenylate cyclase assays, or if high (20 mM) [Mg2+] were employed, then the perceived inhibitory effect of phosphatidic acid was markedly reduced when the fluoride-stimulated activity was followed but was enhanced for the glucagon-stimulated activity. The inhibition of adenylate cyclase activity observed correlated with the association of dioleoyl-PA with the plasma membranes. Adenylate cyclase activity in dioleoyl-PA-treated membranes, however, responded differently to changes in [Mg2+] than did the enzyme in native liver plasma membranes. Benzyl alcohol, which increases membrane fluidity, had similar stimulatory effects on the fluoride- and glucagon-stimulated adenylate cyclase activities in both native and dioleoyl-PA-treated membranes. Incubation of the plasma membranes with phosphatidylserine also led to similar inhibitory effects on adenylate cyclase and responses to Mg2+. Arrhenius plots of both glucagon- and fluoride-stimulated adenylate cyclase activity were different in dioleoyl-PA-treated plasma membranes, compared with native membranes, with a new 'break' occurring at around 16 degrees C, indicating that dioleoyl-PA had become incorporated into the bilayer. E.s.r. analysis of dioleoyl-PA-treated plasma membranes with a nitroxide-labelled fatty acid spin probe identified a new lipid phase separation occurring at around 16 degrees C with also a lipid phase separation occurring at around 28 degrees C as in native liver plasma membranes. It is suggested that acidic phospholipids inhibit adenylate cyclase by virtue of a direct headgroup specific interaction and that this perturbation may be centred at the level of regulation of this enzyme by the stimulatory guanine nucleotide regulatory protein NS.
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D019905:Benzyl Alcohol; D001592:Benzyl Alcohols / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D010712:Phosphatidic Acids / Q000494:pharmacology; D010718:Phosphatidylserines / Q000494:pharmacology; D010743:Phospholipids / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D001592:Benzyl Alcohols; D010712:Phosphatidic Acids; D010718:Phosphatidylserines; D010743:Phospholipids; C037657:dioleoylphosphatidic acid; D019905:Benzyl Alcohol