Guanine Nucleotide-Binding Protein Participates in IgE Receptor-MediatedActivation of Endogenous and Reconstituted Phospholipase A2 in a Permeabilized Cell System

摘要

Activation of phospholipase A2 (PLA2) by the aggregation of receptors forimmunoglobulin E (IgE) can be studied in streptolysin O-permeabilized rat basophilic leukemia cells. Under these conditions, 40 micrograms guanosine 5'-O-(3-thio)triphosphate stimulates PLA2 activity 5-6-fold when free Ca2+ concentrations are buffered at 10(-7)-10(-5) M. Antigen-mediated crosslinking of receptors for IgE synergizes with low concentrations of triphosphate to cause similar stimulation. When the endogenous PLA2 activity is inactivated by chemical modification, we find that exogenously supplied PLAs from porcine pancreas and Naja naja venom is also activated by the aggregation of cell-surface IgE receptors in these permeabilized cells. As with endogenous PLA2, triphosphate synergizes with IgE receptor-aggregation to activate exogenous PLA2 10-fold at 10(-7)-10(-6) M free Ca2+. (jes)